Rough Idle - Dirty Carb or Something Worse?

[l008com]

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.

 

[CraigH]

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.

 

[l008com]

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.

 

[slomo]

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

 

[l008com]

Where is this kill wire?

 

[slomo]

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.

 

[l008com]

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.

 

[slomo]

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.

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.

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

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.

 

[l008com]

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 ?

 

[slomo]

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

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.

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

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.