i know this is an atv forum, but i can't get any help on a dirt bike forum i am on. i rebuilt my son's yz80 and now i cannot get it to idle at all. i replaced both intake gaskets and the "gasket" that goes inbetween the carb and intake. it will not idle unless i put my finger over the carb intake. i have sprayed carb spray trying to find an air leak, but nothing. if i spray into the carb, it does idle down, but i think that is from just choking it out. i have moved the needle adjustment in all directions, but still no change at all. it is a 78 yz. i have gone through the carb, no crap in it too. someone, anyone, can you help?

 

check to see if you put the piston in backwards

 

arrow forward right? if so, arrow is toward front of engine.

 

there is one other thing. if you were sold the wrong piston. some pistons have a hole in the back side while dont. one is for a direct port engine and one is for a piston port engine. does the engine have reeds or no?

 

has reeds.

 

on the back side of the piston does it have three holes? two squarish ones at bottom and a slit above them?

 

i don't think so. don't really remember. hell getting old. it is a wiseco piston. only thing i can remember is the arrow and i put it forward. i am thinking of taking the head back off to reverify, but i am 99.9% sure i did. if it does have the holes, do they go toward intake or exhaust? i don't want to tear it apart if i don't have to, but now i am starting to doubt myself. don't really want to buy another head gasket either, but if that's what it takes i will. i really appreciate the help. the yamaha forum i was on, no one wants to reply. at least i get some suggestions (an really good ones) here. thanks guys. my son and i really appreciate it.

 

The only way an engine can RPM is with an air leak.
Is the slide in correctly? Look down the bore of the carb and check it.
It's getting air from somewhere?

 

after i replaced the gasket between the carb and the intake it actually got better. it originally just raced and had zero throttle. nit it will rev, but will not idle down. i have checked the slide and it is in correct and doesn't seem to be sticking. at first i also thought it might be sticking up. i removed the slide and polished it up. didn't seem to make any differance. still slid up and returned good. i am thinking of trying to locate another carb.

 

figured it out. crank seal blew out and is sucking air through there. what the ^%$^&. pulled my hair out thinking it was something i did wrong and here is something simple.