Running rich when NOT under load

Working on a JD 325 with FC540V single cylinder Kawasaki. It was in ROUGH shape when I got it. Intake valve was stuck open, carb was full of sludge, it was bad. I cleaned the carb several times over like nobody's business. I ended up having to replace the float, main jet, main jet holder and gaskets. I removed the cylinder head, removed the valves. Cleaned up the valves and reset them to spec (.06). Cleaned up the piston head and everything on top of that. I've replaced all the fuel lines, new fuel pump, new fuel filter, new oil, oil filter, spark plug and air filter. I've removed the fuel tank and cleaned it thoroughly. Everything on the mower is working correctly, all electrical and mechanical, hydraulic, all working good. I've run a Seafoam treatment through the engine. The engine runs strong but sputters every few seconds and spits out some black smoke, only when it is NOT under load. If I engage the PTO it runs smooth as silk. Makes no difference if the air cleaner cover is removed.

The air mixture screw adjustment seemed to be making no difference so I removed the air mixture screw and gave it a few shots of carb cleaner directly into the jet. The engine seemed to run smooth (or much smoother) when running the engine with the air mixture screw completely removed. I'm guessing that's my issue.


I'm about to take the carb off and do another cleaning. Before I do that I wanted to see if anyone had any suggestions of anything else this might be. Am I missing anything? I know everyone says it all the time, but I had already really cleaned the heck out of that carb.

Is your carb float set correctly? Try to set it a tad lower so it seats the valve a bit sooner. Just a touch.

It's a plastic float so i can't bend the tab to reposition the needle. Is there another way to do that?

I had a lot of trouble replacing that main jet, the jet I got from Trigreen was waaay too big, even though it showed to be the correct part. I had to get the jet elsewhere based on the Kawasake engine model. If that jet is a hair too big, and I mean a hair, would that cause this problem?

Slight oversize main jet won't effect no load running as much as under load. I suspect you have a partially clogged air bleed on the idle circuit of the carb. You have to mix a certain amount of air with the fuel to help atomize it. Without it you will get raw fuel which doesn't burn very smoothly.

arch252 said:

It's a plastic float so i can't bend the tab to reposition the needle. Is there another way to do that?

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Sometimes, simply holding the tab while raising the float will bend them just enough. Careful you dont break it. I have been know to heat them up a little and push on the tab, while out of the carb, of course

Before you do all that though, remove the bowl and flip the carb and see if the float is really parallel too (or just barely above) the carb, and look at the needle to make sure the tip is good. If the floats way off, or you see wear or on the needle tip, you might need to replace needle and float.

I checked the needle before and it looked fine and the float sat level. I guess I'm going to pull it again and go through it once more. I was hoping there might be some other issue I hadn't considered. This could not be a valve issue could it? I was very careful when I set those, but I was also careful when I cleaned the carb!

Was the valve lash 0.006" and your post a typo or did you really set them at 60 thou ?
Way back you were made aware of the idle air circuit, have you checked it is clear ?
How exactly did you clean the carb ?
many times I have to give them multiple baths in the ultrasonic cleaner.
Did you make the rookie mistake of blowing high pressure air from the filter side in thus compacting any dirt in the fine drillings or did you clean it properly engine side out with low pressure air. ?
If you can turn the idle mixture / air bleed screw any more than 1/2 turn in either direction and the engine does not respond at idle then as you were previously told the passage way is blocked.

You have to clean it out backwards so any crud dislodged passes out through the wide end of the funnel.
Once the front bit is clean, block it off with your finger then spray into the screw hole and look for cleaner coming out into the fuel bowl & /or emulsion tube.

That was a typo Bert. I don't have an ultrasonic cleaner so after I completely break them down i soak them in cleaner and then spray them out with the aerosol can cleaner, I don't use any air at all until I have really worked them over with the carb cleaner. I am familiar with the air circuit but no, I have never considered blowing them out from the engine side, I've never paid attention to which side I introduce the air, but I will from now on. I love learning new tricks. I just spent the last hour and a half going over it again. I paid particular attention to the air circuit and I feel as though I may have freed up some air flow so i feel good about it but won't be able to test it out until tomorrow. This was one of the worst carbs I've seen when I started. If it wasnt so expensive to replace one for that engine I would have. Heck, the float alone was $24.

Yes
an hour or two spent working out how to replace Mikunis with a better priced carb is an hour well spent.
I do a lot of work on Amal concentrics and every one some clot has blown high pressure air through the pilot air seat thus moving all of the crud to the pilot air chamber which has two ,003" holes in it to let the air /fuel mix in under the slide.