Rough Idle - Dirty Carb or Something Worse?

[GearHead36]

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.

 

[l008com]

Yes, and I've also confirmed that the vent (which is not part of the cap) is open. No change.

I mowed my lawn with the machine again today and the dying problem seems to have been solved by the last thorough fuel system clean-out. So now its just the misfiring, I'm leaning towards bad coil at this point.

Aside from the misfiring, this machine works pretty well. It is SUPER light, I didn't know lawnmowers could be this light! But the muffler exhaust is in the front, so as your trying to mow over leaves, it blows them out of the way. Its actually very annoying for someone who typically mulches everything. I will be glad to go back to my primary machine when the time comes. Primary weighs a ton but its self propelled and has amazing suction, its like a vacuum on my yard.

 

[l008com]

Ok I just replaced the ignition coil and still NO change in behavior.

So to recap, I have:

• cleaned the carburetor 3 times
• replaced the fuel line
• cleaned the fuel tank
• confirmed the tank vent is clear
• replaced the spark plug
• replaced the ignition coil
• put in fresh gas and oil
• gapped the valves
• ran with no air filter or muffler (to confirm neither are clogged)
• confirmed the choke is operating normally

STILL this thing runs but misfires. At this point I'm thinking maybe the block is cracked because I don't know what else it could possibly be. What else is there to even try? I also replaced the carb with a new one. The new one had starting problems but once it would run, the engine had the exact same misfiring At this point I might just sell it as is and call it done. What a frustrating project!

Here's one last, fresh video if it misfiring. As always, the camera's mic makes the misfires seem much more subtle than it is in person. Every change in RPM you hear is it misfiring:

 

[slomo]

Stop throwing parts at it. All these new parts require testing. Old parts as well. Test what you have. Keep the credit card in the wallet. Not one time did any of us trying to help you say go buy a new coil.

You need air, fuel, spark at the correct time and compression for that engine to run.

Ok I just replaced the ignition coil and still NO change in behavior.

Could be a bad coil. You are not testing anything as discussed above. Could be a Chinese clone slash black market spark plug causing all of this. You will never know as you don't test anything.

cleaned the carburetor 3 times

Might take more cleaning. You need to search for vacuum leaks while you are testing.

cleaned the fuel tank

Cleaned like a new one? As in zero trash or any 90 degree hose fittings on the bottom packed with dirt and grass?

replaced the spark plug

Needs tested. Doesn't mean it will fire under compression.

gapped the valves

Have to take your word on it. Could of fouled something up. I do it all the time as I am an idiot.

I also replaced the carb with a new one. The new one had starting problems but once it would run, the engine had the exact same misfiring

OEM Briggs carb or a Chinese Gambler Series from Scamazon or Fleabay?

At this point I might just sell it as is and call it done. What a frustrating project!

I hope you don't mean dumping it off on someone else. Better disclose it doesn't run proper in bold letters. People like that I tend to dislike. No place for them in my "try to be honest" world.

 

[slomo]

What does the flywheel key look like? Take a picture or video of the flywheel key and flywheel.

 

[slomo]

Your last video, to me, sounds like the governor spring is/could be fouled up. Sounds like the revs are bouncing around. Hold the throttle plate lever with your finger on top of the carb. See if the revs smooth out. Report back. And don't buy any new parts LOL.

Also verify the choke plate is wide open once warmed up.

 

[l008com]

Your last video, to me, sounds like the governor spring is/could be fouled up. Sounds like the revs are bouncing around. Hold the throttle plate lever with your finger on top of the carb. See if the revs smooth out. Report back. And don't buy any new parts LOL.

Also verify the choke plate is wide open once warmed up.

Flywheel key looks great, nothing deformed or bent, everything looks just like it should. Which you'd expect, the machines not that old, it definitely was still on it's original blade and aside from lots of rust and flaking paint, there was no damage to the blade suggesting it hit something.

Choke definitely opens up fully once its warmed up.

The RPMs are kind of going up and down, but they go down when it misfires. The misfires are not getting captured well on my phone's mic so every time I post a video, i feel like it's a little misleading. I THINK I did put my finger on the throttle lever back when I started working on this thing three months ago but its been so long I don't specifically recall. Ill give it a shot but I'm not expecting much.

 

[slomo]

Watched your latest video again. Not hearing anything out of the norm for that engine. Maybe the governor spring is bad causing the slight stumble?? Hold your finger on the throttle linkage. See if she smooths out. Or put cardboard over carb inlet giving a slight choke effect. Something has to smooth her out. Bad plug, maybe it was dropped or counterfeit fake news black market?

How does it cut under a tall grass heavy engine load? I would just mow with it. Think that carb might not have a pilot circuit. Which shouldn't matter as long as the air fuel ratio is in range running on the main jet. Keep the revs at 3600 and mow away.

At this point, I would worry about keeping the cooling fins clean and lubing the deadman cable on the push bar. Sharpening the blade with a 0 balance side to side. I use an accurate food scale to balance blades. Threw all those plastic and metal cone type balancers in the trash. They would "look" balanced but on the scale be several grams off end to end. Keep the valves in spec. Polishing the ignition coil mounting pads and coil where it sits giving a good ground. Make sure the ignition coil is at 0.006" from flywheel. Checking oil PRIOR to every mow. De carbonizing the cylinder and valves. Check head bolt torque yearly.

 

[l008com]

Watched your latest video again. Not hearing anything out of the norm for that engine. Maybe the governor spring is bad causing the slight stumble?? Hold your finger on the throttle linkage. See if she smooths out. Or put cardboard over carb inlet giving a slight choke effect. Something has to smooth her out. Bad plug, maybe it was dropped or counterfeit fake news black market?
very mow. De carbonizing the cylinder and valves. Check head bolt torque yearly.

Yeah its misfiring about once every second or so, but the mic on my phone doesn't really pick up the miss. It works well, it cuts well. I don't have any SUPER thick grass but in the thickest grass I have, its good. I did try partially covering the intake last time I used it, it had no effect on the rpm/misfiring. I've had the cover off of this thing like a dozen different times this year, the cool finds are definitely clean. I used a piece of junk mail to space the coil, it is suuuper close but not rubbing.

 

[l008com]

Here is a video of me mowing with the machine the other day. On video it sounds perfect because, like I say every time I post a video, the mic doesn't pic up the misfiring, and it misfires about once per second.

It's probably "good enough" at this point, but I'd really love to get it running perfectly if I can.
No I still haven't put my finger on the throttle to make sure the governor isn't acting up, haven't had a chance yet but I probably will later today.