I had a leak from the Oring gasket on the rubber flange. Replaced it and it was good. But mine issue was not intermittent. Does it happen all the time? Notice any difference with compression? Your inlet pushrod is not too tight, right?
You clearly have an air leak somewhere on the intake manifold. My guess is that if there is no cracking, splitting or tearing on the rubber then the throat on the carb is slightly smaller than the opening on the intake manifold. If this is the case what's happening is the clamp is holding the carb tight, but somewhere the rubber is pinched and bunched up causing your leak. I would pull the carb and intake manifold off and give everything a thorough inspection. Look particularly close to the areas where the rubber mounts to the carb to see if the rubber looks distorted.Scottie
A little hard to tell by the description, but I'd try sealing the the carb/manifold joint with some gasket sealer first. Then, if that didn't work, I'd look for more esoteric things like timing and checking the intake valve for leaks.Bare
What's interesting is that sound you describe as 'air being released from a tire'. That represents a pressure build up and release. I can't believe the intake and the draw from the piston would create that kind of pressure. Could it? I'm wondering if there is a back pressure being created back into the carb as the piston rises and the inlet valve is not closed all the way. That could be timing or a valve leak. Since timing is electric, then I can only think of the timing gears being off. But I'd think youd notice the prob all the time and not just intermittently. Therefore, the inlet valve could be leaking for some reason. When you pull the rubber flange to seal it, look inside the carb mouth. Any deposits or signs of blow back into the carb?Just sharing my line of thinking... For what it's worth