Good Evening Gentlemen, I just about have the Cub Cadet 2146 I have been working on wrapped up. It has been tuned up, cleaned up, various things adjusted, and has been tested. I have mowed with it for 4.5 hours, and it runs great. The engine is smooth, starts right up.
However, there is a hiccup. Half the time I shut it off, the engine will run on for a few revolutions, 'dieseling' if you will. I am calling this run on because it sounds exactly like how old, out of tune car engines sound that I used to work on.
Here are some numbers:
Cub Cadet 2146 lawn tractor Model # 13A-224F100
Linamar ZX390 spec # 11317D 14hp horizontal shaft OHV engine
Nikki carburetor (onan model 1460701)
I turn the key off, hear the engine stop firing, and then hear the revolutions wind down. Right near where the revolutions almost stop, the engine fires a few times, and occasionally gives a small pop out the muffler.
I run the engine at idle for 1-2 minutes before I shut the engine off. The following has been done:
-head R&R, cleaned, valves R&R, lapped, new valve stem seals, new head gasket, valves adjusted to .006" cold
-carb completely disassembled, soaked in carb dip, cleaned with brake cleaner, compressed air, and tag wire, soaked for almost an hour in heated ultrasonic cleaner, again cleaned with compressed air and tag wire. Fuel inlet needle viton tip in excellent condition. New bowl gasket and bowl nut gasket. carb installed with new gaskets
-Walbro impulse fuel pump rebuilt, new fuel lines and filter from tank forward. tank flushed and cleaned. Gas is fresh, 87 octane ethanol free, treated with Stabil and SeaFoam.
-New, properly gapped NGK sparkplug, engine has good spark. I have not thought to check to see if it has spark when running on with the key shut off.
-Exterior of engine has been thoroughly scrubbed clean. Now, from mowing, there is a light coating of dust on everything. All the exterior body panels, covers, seals, and vents are in place on this tractor. Engine pulls air from the rear vents on the side panels and from the rear lower part of the dash. A sealed firewall separates the blower housing inlet from the rest of the engine, so hot air is not reingested.
-idle speed is set at 1275rpm(1400 is called out in the Onan E125-140 service manual), full speed no load is set at 3525rpm, 3500+/- 100 is called for in the service manual.
The engine runs like a top, it starts quickly with little to no choke, it accelerates, does not bog down when mowing. Just runs on sometimes.
Ambient temps this weekend were 98-100, and sunny, but I wouldn't think that would matter.
I am concerned, because to my knowledge, run on is caused by a combination of excessive compression, excessive throttle opening, and or high combustion chamber temps caused by lean mixture or advanced ignition timing.
I cleaned the combustion chamber, and saw no sharp edges. I have the idle set below specs, thinking that might help. The carb is non adjustable except for idle speed, so if it is lean, I am up a creek, and there is no way to set ignition timing to anything other than stock.
So, does anyone have any suggestions for me?
Seth K. Pyle
Nothing is sailor-proof...