Rough Idle - Dirty Carb or Something Worse?

slomo

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

RYANS'

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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.
 

RYANS'

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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.
 

Etbrown44

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

l008com

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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.
 

l008com

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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.

IMG_9251.jpg IMG_1547.jpg

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

l008com

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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 :D

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?
 

slomo

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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.
 
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l008com

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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!

 

GearHead36

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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.
 
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