I have a 1989 YFM100 champ that starts and idols fine but dies at about half throttle or when its put under much of a load. (like driving up a trailer ramp). Any thoughts, carb problem or lifter adjustment?? I just got to fix up for my daughter so don't much about it.

 

Check all the major air/fuel components first.
- check the carb for contaminants, clean if needed.
- check the needle valve for damage (might need adjusted)
- check and clean jets/ports

- Make sure to flush the fuel tank/hoses if you haven't (I'm assuming the bike is not in mint condition haha)
-check spark plug/gap
- check coil/plug wire for damage and voltage

basically just start with basics and work out all cheap and simple possibilities first. Chances are you're either gettin too much fuel at mid throttle or under load or not enough spark,

 

I'm on it! Found that the previous owner didn't have an air filter in it so I pulled the card tonight. Hadn't thought about checking the strength of the spark!

Thx!!

 

Ok, the carburetor is shot!! It's ate up inside, looks like someone soked it in a toilet boil cleaner and it eroded the alum. I have an 85 YFM80 that i can take the carb off of, will it work on the 100cc?? Looks the same, jets are the same in the part manual but the main jet nozzle is different and I did notice that the cut out listing on the 80cc is 3.0 and it's 3.5 for the 100cc. What does it mean "cut out"?? Could I modify the carb to work or will it bolt right up and go?