Rough Idle - Dirty Carb or Something Worse?

This is to the OP. If you understood how the fuel, ignition and compression systems work together on a small engine, this thread would have ended 60 posts ago. Reading what you are posting the techs on this forum can see that by not even knowing the names of the components or how that work by themselves and in conjunction with other components tells us your expertise on this subject is very minimal and you are looking for someone to hold your hand and solve your problem. Maybe you should reread post #25. You are so closed minded and your assumptions are absolutely correct, you won’t listen to suggestions given or think that maybe you are wrong. You claim that your $1000.00 phone can’t produce a good audio, as an excuse for us not being able to help you. Did you ever think that your 100% is not achievable on a $50.00 engine? Yes that is what it cost MTD to purchase that engin, and Briggs still made a profit. It’s time you put your ego and false expectations on the back burner and realize your assumptions on how a perfect small engine should run is not achievable.

l008com said:

Choking down didn't seem to affect the RPMs but I feel like it did smooth out the misfiring a bit. It's hard to tell, and none of it is picked up on the camera. But I don't know, it did feel a little smoother.

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Okay this is getting crazy. The main still sounds partially clogged. It does give a little more fuel and less air when choked down. Slightly smoothing out the engine. I hope you fully choked it down.

l008com said:

"throttle plate slash linkage" . . . that what now

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Looking at the top of the carb. There is a choke plate which is physically away from the engine block and there is a throttle plate which is closest to the block ON/inside the carb body. That gov spring with a lot of coils is your throttle/governor spring. You have a rigid linkage from that thermostatic lever that controls the choke plate. Thermostatic lever heats up off the exhaust and moves the choke lever choking the engine down. This increases the air velocity which picks up more fuel off the main jet and its circuit. That enrichens the engine when cold to make her start. Colder air needs more fuel. Cars and trucks use more fuel in the winter. Fuel is not as volatile and so on. That is why we have summer and winter blended fuels. Getting off point.

l008com said:

Also not clear on what you're actually telling me to do when you say "Do a low rev and a high normal rev condition" ??

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I meant hold the throttle linkage on top of the carb steady as in not moving it. If the revs and or misfires steady out, need to look at the governor spring, maybe the governor arm setting on the outside of the block or the internal governor itself. Low revs meaning say 2000rpm. High revs at 3600 full song. Does it smooth out?

l008com said:

Also note, I crashed my mountain bike yesterday and messed up my hand pretty bad so it may be a few days before I'm able to do any of this.

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Well that was bad timing. If you don't already know. For road rash the trick is anti-bacterial cream like neosporin ointment and honey 50/50 mix. Slather it on and wrap in clear Saran Wrap plastic wrap kitchen stuff. Tape it all down. Be surprised how fast it heals compared to all other methods. Honey is anti-bacterial, fungal and so on.

l008com said:

ALSO, second note, all forum posts are optional. You can skip any you don't like, for any reason, no questions asked. As for "isn't 9 pages enough", obviously not if the machine isn't 100% fixed yet.

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I got that. You wouldn't be here unless there was an issue. I'm sure you have other pressing issues like NOT CRASHING YOUR BIKE you silly goose.

Rivets said:

This is to the OP. If you understood how the fuel, ignition and compression systems work together on a small engine, this thread would have ended 60 posts ago. Reading what you are posting the techs on this forum can see that by not even knowing the names of the components or how that work by themselves and in conjunction with other components tells us your expertise on this subject is very minimal and you are looking for someone to hold your hand and solve your problem. Maybe you should reread post #25. You are so closed minded and your assumptions are absolutely correct, you won’t listen to suggestions given or think that maybe you are wrong. You claim that your $1000.00 phone can’t produce a good audio, as an excuse for us not being able to help you. Did you ever think that your 100% is not achievable on a $50.00 engine? Yes that is what it cost MTD to purchase that engin, and Briggs still made a profit. It’s time you put your ego and false expectations on the back burner and realize your assumptions on how a perfect small engine should run is not achievable.

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Sometimes good enough is good enough. Good luck.

No road rash, only severe bruising. Still a bad day biking beats a good day in a cubicle.

slomo said:

Okay this is getting crazy. The main still sounds partially clogged. It does give a little more fuel and less air when choked down. Slightly smoothing out the engine. I hope you fully choked it down.
...

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Ok I played around today. Held the throttle in various positions. It still misfired but I guess the RPMs were a bit more steady. The throttle is SO touchy and of course its an engine so it's vibrating, so its not easy to hold it perfectly still but I did the most I could.

Then I fully closed the choke. The only way to do that on this carb is to first flip the throttle to wide open, so I did that real quick and then closed the choke fully. You can see that in the video. It ran poor but it didn't conk out.

I see some blow-by coming out of the carb. Might want to pull the head and check for a blown head gasket. It's visible all the time you have your hand on the throttle. Look right below your right thumb in the video. See that smoke puffing out of the breather/engine?

Seeing a little black smoke with choke on. Think the main jet circuit is fine. Would be looking into the previously mentioned blow-by. Leak down test and pull the head off time.

Rings, hole in piston and a possible blown head gasket. Hope for the latter. Head gasket is cheap. You MUST lap the head and block where the head gasket sits after surgically cleaning those areas first.

l008com said:

Then I fully closed the choke. The only way to do that on this carb is to first flip the throttle to wide open, so I did that real quick and then closed the choke fully. You can see that in the video. It ran poor but it didn't conk out.

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Disconnect that rigid choke linkage for testing. That rigid piece of wire that connects to the choke. Manipulate the choke plate with your fingers a lit easier. Should stumble down in revs and make some black some out of the muffler.

How would a bad head gasket cause blow by out of the crank vent? Wouldn't the hot gasses still have to get by the piston rings to get in to the crank case?

l008com said:

How would a bad head gasket cause blow by out of the crank vent? Wouldn't the hot gasses still have to get by the piston rings to get in to the crank case?

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IF it is the head gasket, it can have a gasket leak that gets into the push rod tunnel that goes back to the cam and oil sump. From the oil sump out the block breather hose inside the air filter housing. So head gasket to cam tunnel then oil sump. Oil sump to block breather and breather hose that connects to the air filter for reburns.

Some how the block is getting pressurized with combustion gasses that is getting pushed out the block breather system at the air filter. Do a youtube search for blown head gaskets. Taryl and others have several ways to confirm this for you. Like pulling the oil stick blah blah..........