2slow2matter:

There is a known issue with some of the 140 sport engines. I think you should check yours, because it sounds like it might be at the heart of some of your problems.

I have one that I could not get the low end to lean out enough to idle smoothly. After hours of adjusting and re-adjusting, I finally got it to run OK on the high end, pretty good in the mid-range, but it would only idle down to around 3000 RPMs. If I tried to get it to idle any lower, it would run rough, spit fuel, and eventually die. I had the air bleed screw out so far it was about ready to fall out of the carb completely, but it was still too rich. Leaving the glow ignitor attached helped, but didn't completely solve the problem. I finally gave up and called YS, and spoke to one of their chief technicians about it. He listened to my description and quickly told me that some of the 140 sports were made with the wrong size hole in the barrel of the carburator. This hole is the one through which the engine draws air while idling, the one that is blocked/unblocked by the idle screw. He told me to take the barrel out of the carb and drill the hole out to 1/8" inch. (It's the only hole in the barrel) I did and my problem was solved. You might want to check yours and see if it's undersized, as it will cause you to chase your mixture settings all over creation.

If you have to drill the hole out, make sure you don't allow any burrs to remain when you re-assemble it. Reset your regulator screw to flush with the housing, and start the motor. Adjust the high end first, lean it until you see or hear maximum RPMs, and then richen it until the RPMs drop three or four hundred. Now throttle back to around 4000 RPMs and adjust the regulator for best running. You should need only small adjustments here, like 1/8th of a turn or less. Once you have the mid range adjusted, go back and re-adjust the high end. Do this until you can't improve either one any more at all before you mess with the idle. By the way, the high speed screw is a regular needle valve, so CW leans and CCW richens.

Now throttle down to as low as it will run and keep running, and begin adjusting the low speed air bleed screw. Remember, it's bass-ackwards, opposite from the HS needle valve, so CW richens and CCW leans it. Leave the glow ignitor on in case it's rich, until you get it close to correct. Lean the low end for smooth idle, let it idle a few seconds and check the transition. If it cuts out suddenly, it's probably a fuzz lean, if it coughs and sputters and then goes it's probably a little rich. You should be able to get the idle to around 2000-2500 without any problem, and without the need for an on-board glow ignitor. Mine will idle at around 1500 if I want it to, and will idle all day and then spool up immediately when I say "giddyup".

You might want to call YS and talk with them yourself about this problem, after all, I'm just a "voice" on the 'net, but if you'll do a search I think you'll find some previous threads on this problem. I hope you get it worked out, and I hope this helps.

David