1986 Yamaha Moto 4 YFM228 bogs down under load

[chuckcnm]

I have a 86 Yamaha Moto 4 YFM228 that bogs down under load, seems to improve as I go to a higher gear. Does not die but just no power.

new plug

new coil

new pistons and rings, was doing this before a replaced them.

Any ideas

 

[Ajmboy]

Maybe it's not getting enough fuel and the carb bowl is running dry? I've seen on older quads, the float pin gets corroded and the carb then needs a rebuild.

[chuckcnm]

That Was my next step. will order my kit tonight, Thanks

[chuckcnm]

I just found one problem, I took a look at my spark plug, it was fouled with black carbon deposits. looked at my manual, it did not have much to say about any adjustments

[quadmaniac]

Carbon fouled is usually from an overly rich fuel condition. I would put a new plug in it, run it to see if that caused the issue. But more than likely your carb needs an adjustment or rebuild. Also check your air filter, because if its clogged and dirty, you can get an overly rich fuel condition.

[gears]

Exhaust can be clogged too. Did you mess with the needle's clip setting on the carb slide? Does turning the choke on while riding change anything? See if running it with the aircleaner lid removed changes anything - could be restriction in the intake tract ducts (mouse nest) going to the airbox.

[chuckcnm]

I have ordered a rebuild kit will wait till I get before I open it up. Only setting I have mess with is the idle screw. I have been thinking about the choke, will try that tonight. I did pull the air filter off and I am still getting black exhaust and I put in a new spark plug.

Thanks ALL will let you know what I find.

 

[Ajmboy]

Black exhaust is a rich running condition, too much fuel usually. Something is up with that carb if your air isn't restricted.