1980 YT125 wont idle

[Jaydub]

Near the beginning of summer I found a 1980 tri moto YT125. It had a few issues such as no spark and needed a carb kit. I fixed those issues got it started and the main crank bearing on the left side (behind the stator coils) was louder than the engine, so I snatched the engine out and replaced all the bearings, seals, rings and gaskets basically rebuilt the top and bottom. While I had it out I also polished the exhaust port, the combustion chamber, and the intake while leaving it rough enough as to not impede fuel atomization. I also noticed the replacement copper head gasket was maybe 1/3 the thickness of the original and considered annealing the old one and reusing it but thought since the new gasket was much thinner it would increase the combustion ratio a bit so I annealed and used it. After reinstallation and cleaning and rebuilding the carb the engine fired right up but it will not idle unless I hold the throttle slightly. I believe the throttle cable may need to be adjusted because the idle speed adjustment knob doesnt change anything no matter how much you screw it in. The air/fuel mixture screw is set to 1.5 turns out as the manual sugests and adjusting it either way doesnt affect its idle as far as idling without holding the throttle at an idle speed. Any thoughts?

[shortline10]

Check the float level on your carburetor , if the level is to low it can’t reach the idle jet or I’ve seen them were the float is to high and uncontrollably floods the motor with fuel and no adjustment will do anything .
if the air fuel and the idle screw have no effect then there’s definitely something going on with that carburetor
.
There is a quick test to see if the float level is set too high and flooding out , turn the Petcock off and run the motor , after a minute or so if the idle starts to come up or the idle screw will start to work then you know you’re flooding the motor and the float level is off or float valve isn’t working correctly .

[Jaydub]

Thank you. I will do that this afternoon. Ive had a new development since yesterday morning. i started it up yesterday evening and it began idling for about the first 20 seconds. I thought about the float at that time but second guessed myself and thought Id wait and see what ideas others might have when i checked this thread, then decided to ride my other bike. Id had issues with the float, it was over flowing the bowl and gas would just pour out. I believe someone had monkeyed with it in the past (its 44 years old so i have no doubt) and damaged the pin the float pivots on and the float was prevented from closing because it was catching on those gouges. It looked like someone used dikes to grab it and cut into it. I had inadvertently bent the tab that limits how far the float moves so I thought I bent it back to the original shape but Ill check the manual and see what says about the distance of float travel. Thanks again for your time! Ill report back what happens, incase youre interested.

[Jaydub]

Ok, well I was about to tackle to float issue when I went to remove the carb I noticed what looks to be a leak from the much thinner head gasket. I only used it because I assumed it would increase the compression a bit without altering the port timing too much. There’s a blackish color spray on the fin where the headgasket is located. I annealed it and torqued the head like I should’ve I also ensured both mating surfaces were completely smooth and clean. I have to assume the gasket itself is too thin to be able to form a good enough seal. Ideas?

[350for350]

I'd say that you need to find a thicker head gasket.

[Jaydub]

no doubt. I put the original back on. All issues are taken care of.