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Here is video of the machine in question. Funny thing is, on video it doesn't really sound like it's doing anything. But in person, its definitely running rough. You can see at the end of the video, how the handle is vibrating.


Ok so the backstory. This is a trash rescue. It was overfilled with oil and wouldn't run. I drained the oil and gas, replaced with the proper amount of oil and fresh gas. It was hard to get it initially started at that point. I had to use a few squirts of starter fluid. But after a minute, it started running under its own fuel and has ran good since. It starts up with one pull every time, even when cold. But it runs very rough after that first pull for 5 to 10 seconds before it starts running better. Better is relative because it still runs a little rough. It feels like maybe its misfiring but it could just as easily be fuel related.

It has a new spark plug and air filter.

So the question is, is this just an issue of a dirty carb, or might there be something worse going on. Like bad compression or bad ignition coil or something like that?
Once I got the machine starting easy and running well, I put 1 oz of seafoam in the tank, then topped it off with fresh gas. I then mowed my whole kinda large lawn with it. I was hoping that would clean out the carb but it doesn't seem to have had any effect. Possibly it just needs to run longer. Also possible its too dirty for that and needs a "real" carb cleaning. Also possible the problem is something else entirely.

What do you think?

As I'm typing this, the video is playing on loop and its so annoying that the audio recording in the video kind of hides the roughness of the idle. One thing you can gleam from the video is that the roughness isn't THAT bad. Its has never stalled on me or anything. Once its running, it stays running. Its just a little rough, it doesn't run like the honda engine on my husqvarna mower.

Sounds like the automatic choke may be sticking closed or the carb is dirty. To check for the choke issue, pull the air filter off and start it, then look in the carb throat to ensure the choke is open. You will need either another person to hold the handle down or tie it to the handlebar so it stays depressed. Let us know. If the choke is opening like it should, pull the carburetor and clean it well.

Did you check the air filter. With the overfill of oil it may have saturated the filter.

Update:
Yesterday I fired it up, clamped the handle, and pulled the air filter off. No change.
Also regarding the choke, first dumb question, is the choke the FIRST butterfly you see looking into the air intake from the air filter?
If so, then it was opening up fully. It was moving slowly, I don't know if that's normal or not. So maybe its slow and that may be causing the kind of "clunky" start. But once its running for a bit, it opens up fully and I still get that not perfect riding, kind of feeling like misfiring.

Is there anything ELSE that might be causing this, before I dig in to the carb? I would think possibly the spark plug, but the plug looked almost mint. Like the previous owner replaced it after over-filling the oil, trying to fix the "now it won't start" problem.
I just want to make sure its the carb so I don't replace it and still have the same problem.

If everything still points to the carb, I'm tempted to mow my lawn with it one more time, with seafoam in the tank again, before I start taking parts off. Because I love it when the lazyman's fix works.

The choke plate is the one you can see on top, I've never had much luck cleaning a carb unless I take it down and do it manually , the smallest particle of rust or whatnot can be stuck in the jet , take it apart and blow through everything with compressed air and then some WD 40 and reinstall. Also make sure your tank is clean

Yeah so the choke opened slowly but it definitely did open fully.

I have had a few engines over the years that ran rough, and with some seafoam treatment over the long term, they would clear up and run well again. But the plan is to get this thing running good and sell it. I don't have time to mow with it all summer. So I'll probably just do the carb. I also have very bad luck taking carbs apart. So if they're only $20 on ebay, I'll probably just replace it. I know many people don't like ebay carbs but I've had very good luck with them. Very few duds.

l008com said:

Yeah so the choke opened slowly but it definitely did open fully.

I have had a few engines over the years that ran rough, and with some seafoam treatment over the long term, they would clear up and run well again. But the plan is to get this thing running good and sell it. I don't have time to mow with it all summer. So I'll probably just do the carb. I also have very bad luck taking carbs apart. So if they're only $20 on ebay, I'll probably just replace it. I know many people don't like ebay carbs but I've had very good luck with them. Very few duds.

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Pretty please, do not purchase one of those aftermarket Chinese carbs off Amazon, it won't run right. Purchase the OEM carb and solve the problem correctly. They are not expensive. Get the model number off the machine and got to Partstree.com and get the part number for the carb. If you provide me with the model number (it may be under the bagger cover and it is either silver or white or on the rear of the chassis behind the engine). That looks like a Briggs engine?, so probably a plastic carburetor. Alternatively, take the carb to a small engine shop and have it cleaned. They are very simple carbs to clean as there is no low-speed circuit. Simply remove the two screws holding the bowl on, clray some carb cleaner through the brass main jet, remove the pin from the float and spray carb cleaner into the inlet seat, put it back together and pop it back on. Here is a YouTube video with instructions.

Ok I've now mowed my lawn twice with this mower, and its a pretty big yard for a small push machine like this. No change in sputtering/misfiring at all even with all the seafoam I ran through it. I even ran it dry then did a little more mowing with just clean, straight gas, incase I was overdoing it with the seafoam. Nada.

So I'll be replacing the carb and I bet it runs perfectly after that.

l008com said:

Ok I've now mowed my lawn twice with this mower, and its a pretty big yard for a small push machine like this. No change in sputtering/misfiring at all even with all the seafoam I ran through it. I even ran it dry then did a little more mowing with just clean, straight gas, incase I was overdoing it with the seafoam. Nada.

So I'll be replacing the carb and I bet it runs perfectly after that.

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Seafoam makes people feel better, like they did something, the majority of the time. However, usually is not the solution or even marginally helpful. It is always better to keep OEM carburetor and clean first before buying an aftermarket carburetor. That said, I have had great results with most aftermarket carburetors I have purchased.

I have to disagree on the effectiveness of seafoam. It doesn't always solve the problems but it has helped a lot more engines for me than it has done nothing for. Two mows isn't a very long treatment but because I need to sell this mower and finish it's video, I really don't have time to mow with it all summer to see if it works, especially when new carbs are $10 shipped. But I've had very good luck with sea foam actually DOING stuff, and by stuff, I mean making engines that run a little rough, run like they should.

l008com said:

I have to disagree on the effectiveness of seafoam. It doesn't always solve the problems but it has helped a lot more engines for me than it has done nothing for. Two mows isn't a very long treatment but because I need to sell this mower and finish it's video, I really don't have time to mow with it all summer to see if it works, especially when new carbs are $10 shipped. But I've had very good luck with sea foam actually DOING stuff, and by stuff, I mean making engines that run a little rough, run like they should.

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If Seafoam were that good, why am I wasting my time cleaning all these hundreds of carburetors over the years and having the engines run great afterwards? Before I started running a small engine shop, I thought Seafoam was the bomb too.

Because you don't have time to use a customers machine for a few weeks to let seafoam work its magic. But as a homeowner, I have that time.
Also I'm not against cleaning a carb. Well, I am but not like that. Why bother cleaning when a new one is $10. But I'm just saying, it doesn't always fix things but it often will if you use it regularly. I put an ounce per gallon into all my power tool gas and I've had a lot fewer carb issues since I started doing that.

But yeah my boat has 3 carbs and they seem to have bad needle valves that let too much fuel in causing stalling at idle and a smokey mess when you are going slow. Seafoam isn't going to fix that.

l008com said:

Because you don't have time to use a customers machine for a few weeks to let seafoam work its magic. But as a homeowner, I have that time.
Also I'm not against cleaning a carb. Well, I am but not like that. Why bother cleaning when a new one is $10. But I'm just saying, it doesn't always fix things but it often will if you use it regularly. I put an ounce per gallon into all my power tool gas and I've had a lot fewer carb issues since I started doing that.

But yeah my boat has 3 carbs and they seem to have bad needle valves that let too much fuel in causing stalling at idle and a smokey mess when you are going slow. Seafoam isn't going to fix that.

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Good luck creating a proper running machine with the ten-dollar bill. Simply remove the carburetor and clean it thoroughly. It's an uncomplicated process, and you can Watch YouTube videos for guidance on cleaning. Allocate 30 minutes to fix the problem.

Rough idle but seeming to run good at hi speed often points to a vacuum leak . Why ? There's more vacuum at idle speed causing a lean mixture more so than at hi speed . Ben there - dun that with a ford engine .

Hmm I guess I worded this poorly. I don't mean Idle in the traditional sense of the word, I mean lawnmower idle, which would be full RPM.
BUT that said, I replaced the carb today and the old one was missing an O ring that could have caused a vacuum leak, so that alone may fix the problem. It was late at night so I didn't get a chance to test it out but hopefully the engine is now at 100%!

GAH! Update: total failure!

The mower behaves the exact same way, rough starts and sputtering/misfiring while running!

I put the new carb in there, with the gasket that the old carb was missing. I also replaced the short little fuel line it has.

After mowing half my lawn with the same poor running, I went and grabbed my primary mower and swapped spark plugs. I hadn't replaced the plug in this machine because it looked like it was in great condition.

So I swapped the plugs and ran both mowers, no change. The honda mower still ran great with the TB's plug. And the TB still ran like poop with the honda's plug.

The gas tank looked totally clean and it was running on brand new gas.

What else is there? What else could cause poor running?

Edit: here's video of it running. It actually might be a little worse now, at least on startup. Once its running for a minute or two, it's about the same as before.

One thing that's weird, when it starts up cold, it runs extra bad. Almost like it might die out. It stays like that for a minute or so. Then suddenly it changes and goes into what I'll call it's "normal" mode, where it's still misfiring and running rough, but it does so at a much higher and steady RPM. It is totally useable in this normal mode, but it's definitely not running the way it should.

I'm not really sure where to go from here, any suggestions?

I too was a great proponent of SeaFoam until about 10 years ago, but they changed their formula and now I wouldn’t recommend It to my enemies . Waste of money. Read this entire thread and there are three things I see. First the OP is hung up on his ideas and is poo-pooing suggests offered. Second, you need an OEM carb, period. Third, because you’re hung up on doing it your way, you’re missing a key element when solving a surging problem. At no point have you checked high end RPMs. Low RPMs will result in surging, especially when the carb may have a blocked passage way. If it is a blocked passage, I’ve found that unless I can get cleaner to move through it, problem will not be resolved. Read my signature.

Ok well i disagree with some of what you say, but this part I don't understand at all:

At no point have you checked high end RPMs. Low RPMs will result in surging, especially when the carb may have a blocked passage way.

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I don't know what you mean here or what you are suggesting I do?

l008com said:

Ok well i disagree with some of what you say, but this part I don't understand at all:



I don't know what you mean here or what you are suggesting I do?

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Let me spell it out in simple language. Either your carburetor is dirty and needs attention, or much less likely, you have an air leak. Try to open yourself up to people that have years of experience and are trying to help you. When I get phone calls from new customers, I have noticed that it is not uncommon that people are poor listeners. If you can get the mower running correctly, the sense of accomplishment is worth the trouble.

Doesn't it seem unlikely that the original carb was dirty, and the brand new one is also dirty? Seems like in this scenario where I've gone through two carbs, the air leak would be the more likely problem, no?

l008com said:

Doesn't it seem unlikely that the original carb was dirty, and the brand new one is also dirty? Seems like in this scenario where I've gone through two carbs, the air leak would be the more likely problem, no?

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It seems very likely that OEM carburetor is dirty, and that the aftermarket carburetor is not dead on with air/fuel mixture, so not running properly.

Once again you don’t want to hear what Tiger and I are saying. In my couple of years servicing small engines I’ve seen more than one carb that looks clean, but has a blocked passageway. If you are depending just on your eyes to diagnose a dirty carb, there is not much help we can offer. Second, you would not be the first person to get a bad carb off the internet. Finally, if you understand how carbs work on today’s small engines, you would know that the RPMs being set too low will result in surging especially if you have a blocked passageway. In my opinion the ball is now in your court. You can try to solve the problem by having the carb ultrasonicly cleaned, which may or may not work or return the new carb and get one from a good, known source. Either way you need to get a tachometer and check your No Load high end speed against engine specs.

Sounds to me, from your video, that the fast idle or max revs is too low. Crank her up to 3400 or 3600 revs and make another video. Bet she smooths out as she will be on the main jet then.

The second video, where you appear for the second lap, the engine was running longer and seemed to be a little higher rev and cleaner firing. Sounded almost normal.

There is more to cleaning a carb than spraying the outside down. Have you cleaned the emulsion tube or does your carb have one? You have either too much fuel or not enough. Seeing as there is no black smoke puffing out the muffler leads to a lack of fuel. What causes a lack of fuel?

1.Trash in the fuel tank.
2.Internally deteriorated fuel lines.
3.Fuel filter if yours has one.
4.Lack of fuel reaching the carb inlet. 1, 2, 3 and 4 here.
5.Carb float height setting.
6.Carb needle/seat issue causing fuel starvation.
7.Fuel tank vent issues.

Place a piece of cardboard over the air inlet area on the carb. This will cause a choked condition. OR activate the choke slightly. See if the engine smooths out or gets worse.

Is your plug black or blistered white?

Might have a cam that is losing it's max lift.

Betting the combustion chamber is loaded with carbon. It's a Briggs so that goes without saying. Chunk of carbon can cause a valve to hang open slightly. This is not directly your main issue but should be looked at.

Slomo gave you 7 things to check. Others have given more. All good.

Doubt it's the carb, since you have tried 2. However For $10 you could always try a 3rd in a different brand to be sure. My experience with installing over 150 of the the chinese carbs has been pretty good. You can always get a bad one, but where does anyone think a Briggs carb is made anyway?

After the carb and Slomos 7 items, I'd try an inexpensive rubber tip compression tester. It will usually tell you if its valves.

l008com said:

Ok well i disagree with some of what you say, but this part I don't understand at all:

I don't know what you mean here or what you are suggesting I do?

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EDIT: First, I apologize that I wrote my earlier comment w/o watching your entire video. As a consequence of that, I missed the fact that in addition to SURGING, your mower actually is MISFIRING as well, albeit intermittently.

However, like others have said, you're not listening to advice, so here's some more you can not listen to.

"Lawnmower idle" is NOT "full RPM" or whatever you called it. Idle is much lower than full speed, which is probably somewhere between 3,330-3,600RPM. You need a TACHOMETER. Here is a write-up on a cheap, but VERY reliable one:"
Farmshow--Vibratach

I mentioned that your engine is surging (or, what I call "hunting"--for a steady speed, either under load or unloaded, when it should be at a [relatively] steady speed regardless of load. That's the governor's job, to keep the the RPMs as stable as possible, under the varying loads placed upon the engine for a given speed).

Surging can be caused by a bad fuel float valve seat, a leaking fuel float and/or dirt in the carburetor--or a combination of all three. But since you've swapped carbs, this is now a head-scratcher.

Surging can also be caused by a malfunctioning governor--but that is less likely than the chance that you're having an improper fuel/air ratio due to an obstruction in the fuel system.

Use the CHOKE As a Diagnositic Tool:
If it slows down, then your mixture is already too rich, as your hand is acting like a choke and richening the mixture further. As another person mentioned, remove the air filter and slowly, progressively cover the carburetor's air intake (with a LEATHER GLOVED HAND, because FIRE)l and note whether the engine speeds up or slows down. If it slows down, then your mixture is already too rich, the engine will slow down. But if the engine speeds up, then your mixture is too lean (which would again point to a FUEL OBSTRUCTION SOMEWHERE).

There should be a SCREEN on the gas pickup tube inside the gas tank. These can look clean but because their mesh is so fine, they can be clogged and need cleaning or replacing, depending upon design.

As a last resort, I would closely examined the holes that the governor wire hooks into, on the carb linkage, and see if you can tell that it used to be in a different hole by virtue of that hole being more elongated than the other holes. Even if they all look the same, you could still try hooking the governor's control rod into the next hole over from the one it's in, in either direction, and see if the surging goes away. But only do that AFTER you've determined whether or not the engine is reaching its specified maximum RPM. (Yes, You will have to look up what your engine's specified maximum RPM is. Try https://www.manualslib.com/.

And if you do start experimenting with the governor's control rod, CHECK YOUR RPMS as you do so, because if you over-speed the engine, you may get to see what the connecting rod looks like, without even taking the engine apart.

Briggs & Stratton made a good small engine manual, probably back in the '80's. IMO, you need to read something like that, as it's clear, to me, that you need more THEORY AND KNOWLEDGE, to build a basic understanding of how small engines actually work. They now offer manuals for more modern, OHV engines, as well (not sure which style engine you have but try to be Brigg's GENERAL small engine manual and the specific manual for your engine, as well (see the FREE manuals library, linked above). You need to get a basic repair manual and READ it--you will find that many of the questions you're asking are answered by such a manual. Good luck.

Watched the video again. Looks like that plastic Briggs carb. Verify choke is opening or not. Wire the sucker wide open with a bread tie. Test it out a few laps.

Top me, longer it runs the more it smooths out. Like the choke is lazily opening. End of video sounded okay. Again revs sound low.

The mic on my camera doesn't capture the sound perfectly. So it does improve once it warms up, it never gets good. Its always misfiring/hunting. And with the new carb, it also has an awful startup. I didn't see a filter in the fuel tank and now I think its full, or close to it. I'll see if I can run it out of gas today (while mowing) and take a closer look in there. I'll also try covering the air intake and see how that goes. I did check the choke earlier in this post and did confirm it is opening up fully and that does not have any effect on the misfiring.

I'll post a followup tonight and see what I find. if I'm really feeling motivated, I might also try cleaning the original carb and see how that goes.

Whaaaaaat a shitshow today turned in to.

The first thing I did was start up the machine and experiment with blocking the air intake by different amounts. It didn't seem to have any affect on how the machine ran. MAYBE a tiny bit smoother with it half covered, but it still misfired. No meaningful difference I'd say.

Then I decided I'd just clean the old carb real quick and put it back on just to see. Even though that doesn't seem like the problem. So long story short, when you spray carb cleaner in one of the holes that the what plastic triple stack thing comes out of, it dislodges the plastic ring in the middle of the carb. So on the old carb, it jammed the choke closed so I couldn't open it up. I didn't realize this until after I put it back on and ran it for a while. It did a whole series of crazy things, really high rpms, then abruptly going to really low RPMs. It was all over the place.

At that point, I figured what the hell, and went to clean the new carb too just for the sake of completeness. After messing around with that for about 2 hours, with jet or whatever its called not being able to be reinserted, I realized what had happened, and took both carbs apart again and properly reseated that ring and snapped that removable part back in. Now I remember why I always opt for the $10 carb replacement over messing with these things. Not worth the trouble at all.

I have footage of it going crazy, I think at once point it was maybe running on access carb cleaner. But in the end, with the original carb reassembled properly, it has a slightly more stable startup, but it still misfires a lot. I don't think it's misfiring any more than it was, but the misfires don't really pick up on camera. I think it does have a more stable startup now, although the really sketchy startup I think only happened with the new carb. I dunno I'm having trouble keeping track of whats what at this point.

Also gas poured out of the fuel line, which I previously replaced. So it's not a rotten fuel line issue or a clogged fuel line issue.
And when I was reassmebling the bowl on the new carb for what felt like the 5th time, one of those screws into the plastic stripped. So I didn't put it back on to re-test.

But this sure does feel like it is not a carb issue at all. Maybe there was a slight dirty carb issue, but the main problem seems to be something else. But what else? Weak coil? Carbon on the valves? If there is carbon on the valves, will it work itself out if I just keep using the machine?

Edit: Also regarding double checking the holes that the rods go in to, there are only two rods and only two holes. Its all plastic and there are no "optional" holes for adjusting the rods. And the two rods are different thicknesses that match the holes, so you really can't go wrong as far as the rods go. There were not other adjustments I was able to see anywhere on the carb.

I'm watching valve rocker adjustment videos on youtube right now. Looks easy enough, I guess that will be the next thing I try. I do own feeler gauges, but I have no glue where they are, I'll have to search for them first.

You really need an inexpensive compression gauge, and that will tell you what you need to know about the valves.

l008com said:

If there is carbon on the valves, will it work itself out if I just keep using the machine?

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No. There is a comment in ALL mower manuals about removing carbon say every 5 years. Check your maintenance items out in your manual. Clean cooling fins and some de-carbon action are highly over looked. Carbon will not work itself out. Once you de-carbon one you will get your answer. Most have big chunks of carbon say behind valves and well all over the chamber.

My mower does the same thing, I cAn see the governor spring is old. I might get a new one. Not bad for free engine. BS 125cc, looks like yours with plastic everything.

Maybe the flywheel key is broken and the engine is miss trimmed. Great video I can hear the miss. Man how annoying are those things you can't fix.

You might be chasing a ghost here. The video sounds just fine. The real test is if it cuts ok.

It is definitely misfiring a lot, the tiny mic on the iphone camera doesn't capture the sound great. If you could hear it in person, you would not say it sounds fine.

The drama continues. So last night I went to check out the valves. I was expecting them to be too loose, because thats what I always see on youtube. But turns out mine were too tight. Very tight. So I tried loosening them. And wouldn't you know it, the tip of my T10 socket snapped right off! Luckily I was able to get it out pretty easily with a powerful magnet. I should have a stand alone T10 driver in my computer tool kit I can use, but it wouldn't be a "yardwork with john" refurb project if every possible thing that could go wrong, didn't go wrong! lol.

Valves too tight would prevent them from closing fully though, correct? So this could be the cause of the misfires. I'm going to try to work it out tomorrow and see if I can get it dialed in just right.



And no, I wasn't turning it super tightly, i was very surprised that it snapped like this.

Ok I was able to properly adjust the valves tonight. They were both a little too tight, but not too bad.
Put it back together, fired it up, zero change.

I'm really running out of ideas. I guess theres that keyway thing people have mentioned. Although this machine is so new, I doubt that would be it, but I'm running out of ideas fast. So about the flywheel key, if the key was broken, wouldn't the flywheel essentially just spin randomly?As opposed to being off a few degrees? I'll have to take it off later this week and see if I can see anything.

For now, it is running much better with the original carb than it did with the ebay carb. So I'll probably just start mowing my lawn with it again while I try to figure it out and maybe it just magically gets better

Here's video of it running tonight, post-valve adjust. The mic on my phone doesn't pick up the skipping very well, so its not running as smooth as it sounds here. And even so, you can still hear misfiring if you listen close. Also the choke is open but I had warmed up the machine before I took this video. I don't know if it was open at that point or if it is operating normally. But a stuck open choke would only affect a cold engine wouldn't it? Once it's warmed up, it should run totally normal?

Dude, that is SPOT ON. I hear zero missing slash misfires. It is a mower with cheap ignition components. Not some fiber optic ignition pickup kit mega blaster deal.

Mow some tall grass and take a video. Meaning put her under load. Again this last video tells me you did a good job repairing her. Mow with it guy.

Watched again. Yup it's not 100% clean firing. Still will pass for a good running mower, I think........ Toss in a parts store bought NGK plug and mow with it.

It was misfiring, the issue is that the mic on the phone doesn't pick it up. It's clearly missing and the whole machine kind of shake-rotates when it misses. It's doing it every couple of seconds. I need a better camera & mic to pick it up though.

ALL THAT SAID, there have been some developments!

While it's still misfiring, it does seem to start up easier and run a little bit better since I cleaned the carb. So I figured no matter what is wrong with it, it would benefit from being used.

So today I mowed my lawn with it. It was still missing every few seconds, but otherwise it started up very easily and ran well.

For about an hour and a half. Then suddenly it died as if it had run out of gas. When I tried to restart it after confirming it had plenty of fuel, it would fire a few times then die over and over. I let it cool for a bit then restarted. It did start but it ran VERY rough and eventually started to backfire. This behavior all came out of nowhere! Video below!

So what do you make of this? I was actually thinking as I was mowing, "eh maybe this is good enough, maybe I just sell it like this". Good thing I didn't!

Have you cleaned the carb and tank? I had a problem something like this with one of the newer Briggs with plastic carb. It would run fine, then act like it was out of fuel, sputtering a bit, then dying. I cleaned the carb. The bowl had water & lots of trash. I took the carb apart, poked wires through various places, and reassembled. Ran fine for a while, then did the same "running out of fuel" thing. I drained the carb bowl, and the gas looked good, but it was full of trash again. So I took off the tank, cleaned it and the fuel line. It's run fine since then.

Yup I cleaned the carb the other day, took it all apart, sprayed everything. The tank looks totally clean and has seen several tanks of fresh gas so theres no old fuel anywhere.

Would a dirty carb cause backfiring out the exhaust?

l008com said:

Yup I cleaned the carb the other day, took it all apart, sprayed everything. The tank looks totally clean and has seen several tanks of fresh gas so theres no old fuel anywhere.

Would a dirty carb cause backfiring out the exhaust?

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Doubtful. I don't recall... have you checked the flywheel key? Backfiring would make me suspect the key.

I didn't check the key yet no. It seems strange that it would be that though. The machine ran - not perfect - but pretty good for an hour straight and suddenly it forgets how to run. I'll see if i can check the key Friday just for the hell of it. And I'm thinking ill replace the plug too since theyre only a few bucks. But I don't expect either thing to work :/

Did some poking around tonight.
Double-checked the spark plug. Either this plug is mint, or I don't understand spark plugs. So I'm assuming its not the plug.


Then I finally got around to popping the flywheel off. The key looked perfect, no sheering or gaps or looseness or anything like that.


On to the muffler, I wanted to make sure there wasn't a screen in there that was somehow clogged up. There was not.


Then while that was off, I figured I might as well take the cylinder head off. It was a little dirty in there but I didn't think it looked TOO bad. Like not too bad to run. But looking closer at the pic, one of the valves DOES look open! And with it pulled that far off the block, the rods should be a mile away from being able to push it open, right? So the springs should absolutely have closed it? That's what I'm thinking. I couldn't get a great view of it or play with it because the carb was still on there so I couldn't pull it off very far.

The port thats open, is that the intake or the exhaust? If it's the exhaust, could it just be jammed up from a piece of carbon breaking off and getting in there somehow? If thats the case, how do you fix this? Just take it all again and manually push it back and forth until it frees up?

Flip it over and check the height of the top of the valve relative to the floor of the head
The valves and the springs are the same length so the valves should protrude the same distance
IF not them either there is crud stuck under a valve or the guide has shifted in the head
The latter happens when the head overheats which is usually from having crud in the cooling fins or a defective blower housing

It was running on and off for a over an hour the day this happened, however there is zero crud anywhere, so it seems very unlikely it would be overheating. I'll have to take the carb off again, then I can take the head off completely and take a closer look.

If it is just some crud, do I just clean with carb cleaner?

Depends where it is
Baked on carbon gets removed with spraying water into the carb with the engine running flat out
Use a misting sprayer because too much water = cracked head
Search decoking with water lots of videos showing it done, mostly on 2 stroke mowers & motorcycles .
You can measure the valve heights just by removing the rocker cover
While you are there measure how far the rockers move the valve stems as well.
The grind on the cams is identical but it is not unknown for one lobe to wear almost round , or a follower to break
Also make sure both valves have their lash caps on

Ok I took the valve cover off and the problem became very clear. One of the rockers fell off. I was able to press down the valve by hand and snap it back in to place. But how did this happen in the first place I wonder? I did JUST adjust the valves, they seemed too tight, so by internet specs, I loosened them using a feeler gauge. But now one fell off. So maybe the internet doesn't know shit and I should have kept them nice and tight?



What would cause a rocker to fall off the valve like that? Is there anything besides being too loose that could cause it?

So it felt like the set screws had loosened up a lot, even though I had tightened them good and snug with my T10. I re-tighten them after I readjusted them, squeezing as hard as I could with my T10 driver but no luck. Is there a trick to this? The first T10 (bit) I used snapped when I was trying to initially loosen them. I can't get them back that tight, not with my hand driver anyway.

Another thing I don't udnerstand. I was able to pull the cord and get the machine to fire a few times before it died again.
If the intake vale is stuck closed because the rocker isn't touching it, how was the engine able to run at all? That doesn't make sense to me?

I haven't had time to even try to start this machine yet. But I was sitting around yesterday and I realized that the rocker would have fallen off when I took the engine cover off. Meaning the rocker isn't the problem and I fully expect this thing to run like crap again once I try to start it up. Guess I'll drain the tank again and try to clean the carb again. Even if I don't get it to 100%, I guess any change in the way it runs will indicate its carb related, and no change at all will indicate its something else.

Plug gap looks too tight. Open her up to your engine spec from your engine manual. Most are 30 thou. Check you manual out. Get rid of that Champion plug while you are at it.

Valves look okay. Can you spin a valve with your thumb, valves closed? If so the valves need lapped and are not sealing.

Rockers come off due to retaining screws backing off or when most everyone on Earth neglects their cooling fins. Valve guides can move from over-heating the engine. Mostly due from lack of maintenance. Need to check the valves YEARLY for a good running machine. Takes 5 minutes out of your busy day. Perfect winter project.

l008com said:

So it felt like the set screws had loosened up a lot, even though I had tightened them good and snug with my T10. I re-tighten them after I readjusted them, squeezing as hard as I could with my T10 driver but no luck. Is there a trick to this? The first T10 (bit) I used snapped when I was trying to initially loosen them. I can't get them back that tight, not with my hand driver anyway.

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Hand driver is plenty tight. Make sure the rocker stud is tight and thread locked in. You don't need NASCAR torque on any of these tiny bolts/nuts.

l008com said:

Another thing I don't udnerstand. I was able to pull the cord and get the machine to fire a few times before it died again.
If the intake vale is stuck closed because the rocker isn't touching it, how was the engine able to run at all? That doesn't make sense to me?

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Might have residual fuel in the chamber lighting off. Nothing to worry about.

Make sure the valve cover is NOT dented inwards. It can and will hold a valve or two open.

The rocker issue was just because I took the engine over off and didn't realize that removed the pressure holding the rocker on to the rods.

So I'm just going to drain the fuel tank again, remove and clean the carb again, and see what happens. The fuel tank looked plenty clean to me, but maybe since it will be empty anyway, I'll clean it with some soapy water.
Then I'm going to put the same fuel back in. That fuel is not old, it's new. But its been in a tank that theoretically could be dirty. So it could have some dirt in it. SOOO whats a good say to strain the fuel, as a precaution? Like a coffee filter maybe? Something like that?

l008com said:

The rocker issue was just because I took the engine over off and didn't realize that removed the pressure holding the rocker on to the rods.

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Do you mean valve cover? If so the valve cover doesn't hold anything on other than itself and or maybe a gasket.

l008com said:

So I'm just going to drain the fuel tank again, remove and clean the carb again, and see what happens. The fuel tank looked plenty clean to me, but maybe since it will be empty anyway, I'll clean it with some soapy water.

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You need to FLUSH, BLOW and reverse blow the tank out. If you have a 90 degree hose barb on the tank outlet, make sure you have flow there as in a good solid stream. Be looking at where you can't see inside the tank. Not just in the bottom and call it good.

l008com said:

Then I'm going to put the same fuel back in. That fuel is not old, it's new. But its been in a tank that theoretically could be dirty. So it could have some dirt in it. SOOO whats a good say to strain the fuel, as a precaution? Like a coffee filter maybe? Something like that?

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Not advised. Any grit being smaller than you and I can see will go right back in where you don't want it to.

Last night, I took the tank and carb off again. I soaked the jet in carb cleaner, then sprayed out all the holes and all of the bowl and body of the carb again. Then I put hot water and some dish soap in the tank and shook it vigorously. Repeat a bunch of times. Then flush with tap water for a while.

This tank is as clean as I can possibly get it, as is the carb.

Right now its sitting out back drying out. Tomorrow or the next day, I'll throw gas in and pull the cord and see what happens. Hopefully it starts right up and stays running.

This may sound strange but pull the muffler off and heat it up really well with a torch to burn out any oil and carbon that has likely collected in it. If exhaust cannot get out, fresh air cannot get in, I deal with this issue more often than I like these days.

Also sharpen and balance the blade or replace it. Being a junk rescue, there is no telling what could have happened with the blade before you got it.

Last but not least, does it need a valve adjustment? This is a maintenance step that is often overlooked or avoided. There are plenty of videos online that demonstrate the procedure, you just need to make sure you find the video that applies to this particular engine. Most of them I deal with gap at .005 inch.

This engine likely has a compression release mechanism on the camshaft, so conducting a compression test would show to be lower than what you would expect to see.

This has been an ongoing saga, I've already done all of those things at this point. Except testing compression, I still don't have a gauge. The machine isn't in that bad of shape probably because it's only 6 years old.

This is really starting to drive me nuts.

After cleaning the carb as thoroughly as I can, including soaking the jet in carb cleaner for a few minutes, then spraying out both ends of every hole with the stuff, and after cleaning the tank with soapy water for an hour, I let the machine sit for a couple of days to let any water dry out.

Today I put more fresh gas in and fired it up. It started right up and ran damn near perfect, for a while.

After a minute or so, the misfire returned. But still the machine was running and running well, just not running perfect.

So I ran down to autozone and got a new spark plug. I threw it in and fired it up.

It has a rough initial start but I feel like that could have just been machine oil on the plug burning off.
So after a minute it was back to running well, with the misfire. I was about ready to call it "good enough", thinking maybe I'm just used to a honda lawnmower engine, maybe this is just as smooth as B&S engines run. . .

Then it started to die. It saved itself, then a few second later, it died. It was like it ran out of gas. But it has tons of gas. I started it back up and it ran rough for a few seconds, then died again.

It sure seems like the carb is clogging up and isn't getting enough fuel. But I had carb cleaner streaming through every tiny hole in that thing. I really don't know what else could possibly be causing this thing to run so bad? The only other part I can replace is the ignition coil, and those aren't too expensive. But it seems more like a furl shortage than an ignition issue.

Also keep in mind the engine was sputtering even with the new carb too (that I later returned).

At this point, I'm at a complete loss. What else could it be? I've replaced or checked everything but the coil, however this doesn't look like a coil problem.

I had a similar problem with a mower, if I leaned the mower backwards when it tried to stall, it would keep it running well.
I tried cleaning the tank, cleaning the carb (multiple times), replacing the plug, regapped the coil, regapped the new plug, checked all gaskets and replaced any that went perfect.

The problem would normally come about if I bumped the front of the mower into something when mowing.

Even after all that work the problem was still there.
Then one day when I used it, the problem was gone, no reason as hadn't touched it since the last time I mowed.
Since then it's ran fine (that was over a year ago).
Still have no idea what the issue was.
I keep thinking it was something lodged in the carb somewhere that I couldn't get to or see, but I'd out wire through all passages and carb cleaner through them before and after.
It's a year since I did all the work and it still runs great.

The whole point of this project was to make a video where I fix up this machine and sell it. But I really don't want to sell a mower that I'm not confident is working properly. So I'm not really sure what I'll do at this point. I have my own much nicer mower, I have no need or desire to keep this one long term. It was just a fun fixup video project.

Pull the kill wire off the coil. Should run the tank dry if the ignition coil is good.

Where is this kill wire?

You have a high tension lead which is the plug wire and a small gauge black wire (kill wire) that connects to the ignition coil. If the kill wire ever grounds out the coil, you have no spark.

Also remove the coil. Polish the mounting pads where the coil sits and the area on the coil where it mounts. Clean all the rust off here.

Don't worry about rust on the flywheel. Has zero to do with magnetism.

You also need to load or stress test the coil. Needs to jump a 0.25" or 1/4" gap in free air.

Ok I found the ground wire for the coil and unplugged it. I put a little electrical tape on the coil side connector to make sure it doesn't try to arc over to the engine block. And I taped the wire to the plastic body of the mower so I don't loose it or melt it on the muffler.

Its too late at night so I didn't have a chance to start it up and test it, so I'll have to see when I try to mow my lawn with it thursday or friday.

But that gives me time to ask follow up questions. With this ground wire unplugged, what exactly will happen when I let go of the man lever? Will the engine brake come on, but the engine will keep running? Is the brake not enough stopping power to kill the engine? If so, does that mean i have to pull the spark plug to kill it?
It probably won't come to that because I suspect its still going to stall out after a minute or two.

l008com said:

I put a little electrical tape on the coil side connector to make sure it doesn't try to arc over to the engine block.

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Not needed but not critical. Remember to use some alcohol to clean that connector when you are done testing. Remove the adhesive from the tape. It will attract grit and grime.

l008com said:

what exactly will happen when I let go of the man lever?

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IF the coil is good, the engine will run against the flywheel brake. You will need to strap the deadman lever to the bar leaving the engine running, for testing only. Should run the tank dry IF the coil is good.

Ok update time.

I unplugged the coil's ground line and started it up, no change in behavior.
While I was at it, I also fully removed the muffler and started it up, just in case it was clogged internally in a way I couldn't see, no change in behavior. Except people a mile away could hear what I was doing

So I figured what the hell, I took the carb off AGAIN, took it apart again, spilled fresh clean fuel all over the place, Got carb cleaner spraying through the jet like... well like a jet, again. I reassembled and . . . .

I started it up and it ran perfect! For a while . . . The dying problem was gone, but even the misfiring was gone for a while. I was mowing away for a while. Then once the machine warmed up, it started misfiring again.

Its one misfire every 1 to 3 seconds on average. It didn't seem to be getting worse, and I did run it in my driveway for a good 15 minutes or so afterwards to see what happens.

I also poured some more seafoam in the tank, and put a few cap fulls directly into the carb while the machine was running in the driveway. I'll mow my lawn with it again next week and see what happens. If it gets better, than it's mission accomplished. If it stays the same, I'll still probably call it mission accomplished. If it gets worse, I dunno. The carb is clean, the fuel line and tank are clean and new, the gas is fresh, so I have no idea where this dirt that keeps clogging it could be coming from. Its the same gas I put in all my other machines that run great. BUT maybe it won't get worse, maybe its really fixed this time. Fingers crossed!

I do have video of it barely running at all before, then running great after, then running well but misfiring well after. But I'm not going to bother to post unless anyone specifically requests to see ?

l008com said:

I unplugged the coil's ground line and started it up, no change in behavior.

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You need to verify you have solid spark all the time you are holding the deadman lever to the bar. With a good coil, should of ran perfect IF it was a spark issue. You could have a partial failure in your ignition coil? Never seen one but it is an electrical part. Coil gets hot and starts sputtering???????? Did you remove the coil polishing the mounting pads and such? Coil needs a good ground.

Does your gas can have a good cap to it? Is there any grit in the bottom? Is this a new type gas can or an old one with the cap removed letting dust, water, bugs, grass and so on inside the can? If you have an open or old style, you are contaminating your fuel system passing grit to the carb.

l008com said:

Its one misfire every 1 to 3 seconds on average. It didn't seem to be getting worse,

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So your word is misfire. Back to the coil again. Get one of these. The Oppama PET-4000 is supreme. You need to rule out SPARK as a cause.

Have you tried removing the gas cap? The symptoms point to a possible clogged vent. Some caps are vented. Some vents are in the tank.