What are you using for air boots and intake I thought of this for a evo bike but they dont allow flat slide carbs . If I were to try it Id think like 55 pilot 170 main 6.0 slide or so. dont take these as specs butthats what Id try first.
I hope your '90 490 motor is better than my '84.
I have just plain given up on that thing after two bore jobs, two pistons and many hours of trying to figure the jetting out i have come to the conclusion it just cant be done without professional work from EG or the likes. Im savin my money for a late model YZ250.
The Carb is a 44mm Mikuni, On the second rebuild i sealed everything up pretty well and the base and head gaskets leaked a bit then sealed up after retorquing, then the exaust started leaking. The only other leak on the intake side was where the throttle cable nippled up into the top of the carb. I used all new gaskets and yamabond sealer. The wife has pretty much nixed trying to fix this one again, but suggested looking for something newer :yeehaw: