1986 Xr Question

A guy I work with has an 86 xr 650 (I think), anyways it smoked like cancer patient so I rerung it and replaced the valve stem seals. The smoking is gone but now it cuts out on accell. If you take the side of the airbox off it runs like a champ so he drilled some air holes in the box and it seemed to run ok. He then noticed that air was actually blowing out of the holes he drilled. That just doesn't make since to me it should be sucking, the bike seems to run ok idles fine etc. Anyone ever run into something like this. The engine does have 2 carbs maybe one side is blowing and one is sucking???????

A guy I work with has an 86 xr 650 (I think), anyways it smoked like cancer patient so I rerung it and replaced the valve stem seals. The smoking is gone but now it cuts out on accell. If you take the side of the airbox off it runs like a champ so he drilled some air holes in the box and it seemed to run ok. He then noticed that air was actually blowing out of the holes he drilled. That just doesn't make since to me it should be sucking, the bike seems to run ok idles fine etc. Anyone ever run into something like this. The engine does have 2 carbs maybe one side is blowing and one is sucking???????

check the crankcase breather/tube for an obstruction maybe?? that doesnt sound right though. if it runs ok\there is no way it would be pushing air out the intake, or at least i've never heard/seen this! prob just feeling the air rushing into the intake.

if it helped by opening up the airbox then it was too rich originally, clean the air filter? where is your fuel screw set at?

I agree the whole thing doesn't make sense. He purchased the bike used and smoking so I don't know how well it ran before hand. He says if he puts a rubber glove over the hole he drilled in the air box it inflates when he revs it. I've cleaned the carbs and the filter is good. the bike will fall on its face when you accell unless you take off the seat or side panel

only thing i can think of was if the blowby was bad enough it could do this. did you check the piston to cyl. wall clearance? did you hone or have a machine shop bore it?

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