Does the compression release ever break or malfunction where it is always engaged so as to affect the low speed and need full choke to run at full speed?
new carb and no dirt or restriction as I replaced all lines from the tank and filter with fuel flowing freely. It appears to hiccup or fart occasionally, but not backfire. Full choke runs the best but runs at a higher RPM, Compression gage read 90 psi in about 4 revolutions.
According to the number, this is a single cylinder push mower engine. Does it have an auto choke function?
Compression release is only to aid in engine cranking at startup so it can spin faster. If it were not working the engine would fight the pull starter while trying to turn.
This sounds more like you possibly have a vacuum leak between the carburetor and the engine intake.
An ignition coil or spark plug failing can do some strange things like this as well.
It is a 38" riding mower. I pulled the head again and lapped the valves today and they were ok as I suspected. I also looked at the flywheel key and I adjusted the gov. I put on another carb which is a little better but it pops and farts intermittently. It must be a worn camshaft.
I was thinking if the compression release broke off but the pin remained in bump position it my do funky crap.
done all of that. It seems to pop on the exhaust side and fart back through the carb. I may try a coil and plug but I am now wondering about a worn cam lobe.
No, I did remove it to clean and make sure rust was not interfering with the ground. Would a coil act up on slower RPM?
I also pulled the flywheel bolt to look at the key from the top without pulling the flywheel loose. When I accellerate it by hand she sounds good, but slow idle speeds are crap or stall.
First, how did you set the air gap when you removed the ignition coil and reinstalled it. The simplest way to set this air gap is with a plain paper business card placed between the flywheel magnet and the coil. Loosen the mounting screws of the coil and let the magnet pull the coil in to pinch the card between. Tighten the screws, then rotate the flywheel by hand while you gently pull the card out.
Next is the spark plug electrode air gap. They seldom come "preset". This gap should be set at .030 inch.
Once that is done, the carburetor would be next. Is this a Walbro style carburetor with the solenoid retaining the fuel bowl to the housing, or a Nikki style that has 2 screws holding the fuel bowl onto the housing? Both designs were possibly used with this engine.
From the running description this favors a "lean misfire" issue and that is usually an internal carburetor related problem.
I've been using "knock off" copy carburetors for a number of years and most have been good, but there is very little if any quality control. That means there can be a potential for issues like this from time to time.
These small engine carburetors have 2 basic "circuits". They are low idle and high RPM, but they also have an idle air bleed passage that meters the air has fuel is drawn into the carburetor.
If it is popping back slightly at idle that usually involves a restricted bleed air passage. It could be a poorly machined carburetor or simply too small for the specific engine application.
It could, mostly weak coils fade at mid and high revs. This is where the Christmas light coil testers do not show you the whole picture of can said coil jump a large gap in free air. We hav better tools now as in the PET-4000.
