On my 98 883, there are two hollow allen bolts that bolt the carb backing plate to the heads. I've got this puffing action going on with air blowing in and out through the center of these bolts. It is really loud at an idle, almost a whistle, but it puffs very quickly. It is not hot, so it wouldn't seem to be exhaust. If I hold my fingers over these bolts, the sound goes away, and the air pushing out, nor the suction pulling back is very strong. I just finished converting it from 883 to 1200, and am using the 883 heads. Of course it has new rings. It is like it is venting pressure off the top of the head. Is this some kind of emission control gone crazy?Anybody run into this before? Any idea what is the cause? What if I just block those openings? Otherwise, motor runs perfect. Thanks for you help.

 

Those are the engine breather bolts, they need to be open!!!!! And yes they should be puffing air in and out.

 

I don't remember it being that loud before. Maybe I am just parinoid with a new engine. Think it will settle down when the rings get seated??