Help Diagnose a wierd sound?

So here is the back story......

I changed the plugs and exhaust ghaskets on my KZ650, all stock aside from a K&N air filter.

I had a large gaping hole behind the cross over pipe in the header so I mended it and reinstalled the exhaust.

After starting it up, I had a large improvement in low end performance, the exhaust note was much deeper and the amount of pressure coming from the tailpipes was a lot higher. (Glad I found that leak, I was wondering why my left foot was so damn hot all of the time.)

So yesterday, I pulled off the points cover and did the 2 turns of the crankshaft, backed out the tensioner, and screwed it back in. THe engine is a lot quieter now, BUT...............HERE IS WHERE IT GETS INTERESTING....

The bike starts up fine and pulls with a little more vigor, but it makes this "ppph, ppph, ppph" sound from time to time, like in the cowboy movies when he guy spits in the spitoon. Runs fine, gear down "ppph" everynow and then at idle it will "ppph" and leaving the garage it makes the sound .

I thought it was coming from the newly installed exhaust ghaskets, but I think that it coming from the carbs, is that possible. Can it spit hot exhaust back through the carbs, is it too much pressure with the new exhaust ghaskets, or should I get the valves checked?

THe bike runs fine other than this sound, I did a speedo 100mph yesterday, but I hear that it is just 90mph in reality.


Any comments, think the valves need a look?

KRB)

yes look at the valves, you may have one tight. also look for some vacum leaks, around the intake boots

Would also double check for any recurrent leakage from the repaired header cross over pipe.

As known, 4 strokes = intake, compression, power, exhaust.

A too tight intake valve (not fully closing when seated) may sometimes allow combustion to spit back through the carb, especially on the power stroke when both valves are supposed to be fully seated and closed.

Good Luck!