Is there a compression/vacuum overlap?

Kind of a follow up from a carb question. Is there a blowback out the carb during overlap of the valve closing/opening? When I try and start the bike and put a hand over the carb there is a moment of blowout before the vacuum. In other words it blows for a moment before it sucks. Is this normal or is it possible that my cam chain off a link?

KZ650 750 juggs and cams. K900 A4 carbs. Points are new and set. Carbs are squeaky clean and all passages and circuits flow nicely.

There is some cam overlap where both valves are open. I don't know how much blowback that should create, but it's possible there is some.

I have heard of this more with aftermarket (hotter) cams, not so much with stock cams but there probably is a little.

have you made sure the valves are set right, might be a little tight

does it happen with all carb's or just one in particular.

If cam timing is correct, would suspect intake valve is failing to fully seat for whatever reason (such as too tight clearance or a burnt seat). May cause backfiring through the carb as some of the combustion bypasses the supposedly seated valve and flows back out the intake port and carb.

Good Luck!

you read my mind sir

I apologize Gentlemen. I've been bouncing around on a few threads and lost track of this one. As it turns out I mis-counted the links when reinstalling my cams and was a link off. It also obviously caused me a lot of other grief. Took her apart, reset the cams and she fired right up. No more blow out cycle.

The combination of problems should have connected me quickly to look at the chain but I was just so darn "sure" that I did it right LOL. Too many years wrenching on 2-strokes. Live and learn as they say. Bikes running pretty well. Still some jetting to work out but so far so good. I am really starting to like this bike.

Thanks much as always for the tips!