M4ATVfun

I received this YFM80 ATV in a no run condition, so it's possible that incorrect parts are responsible for this problem? Before I search for other causes l want to install the eBay replacement CDI (being shipped from China). Thanks for the useful ideas I will research these suggestions in the event that the new CDI doesn't resolve this issue.

Thanks Mech for taking the time to reply. Your suggestions are all very good and relevant. The Magneto keyway is intact and possitioned correctly, the valve sprocket is also correctly aligned, the reluctor gap is correct (.028). The spark jumps the .028 gap on the plug. When I crank the engine with the timing light connected I'm seeing that the timing is advanced by 60 degrees. I've ordered a motorcycle CDI from eBay the seller states that it will work on this engine. I'm hopeful that after I splice it into the harness that it will correct the timing issue, but am sceptical. I was wondering if other people have experienced this part shortage issue and how they solved this problem.

I'm trying to fix a 1986 Yamaha yfm80. I suspect that the CDI is bad since I get spark but my timing is 60 degrees advanced, I can't find a new or reasonably priced used CDI. I was wondering if anyone knows of an alternative CDI that would work? If a CDI from a later year YFM80 could be spliced into the ATV or perhaps from different Make/model ? that would produce the correct timing for this engine

I believe you have a carburetor issue, my guess is the primary carburetor jet is clogged. I would remove the carburetor bowl and remove the larger jet and clean the tiny hole that runs through the center of this jet as well as the tiny holes on the jets sides. You can buy the professional jet cleansing brushes or to save money find a piece of stranded wire and remove one strand and use that to clean the jet. This clogged jet can be difficult to clean and sometimes you need to buy a new jet, the size of the jet is marked on it (you'll need a magnifying glass to read it).