Memoirs Toilet Bubbling

Memoirs Toilet Bubbling???

Just installed a new Kohler Memoirs elongated toilet in a totally remodeled 2nd floor bathroom. (DWV is original copper, flange is new) Used a Fernco waxless seal. No leaks. Every time I flush, the jet in the bowl gurgles a bubble and then everything flushes well. Can't figure where the bubble is coming from. I just flushed the vent pipe from the roof down and it seems clear as does the drain.

Called Kohler and their tech said it could possibly be a flaw in the internal trap or an air leak somewhere in the bowl. They said they would send me a replacement authorization.

Does this sound possible to any of you or am I missing something in the vent system?

Bump^

Just trying to get a few ideas.

Still thinking..............

Kohler may have it, I can't figure it out.

Tried dumping a 2 gal bucket of water down the toilet to see if I get a bubble and voila, no bubble, no gurgle. This tells me that the drain/vent is not the problem.

I suspect the serpentine casting in the bowl that leads to the main jet at the bottom of the bowl possibly creating a small air block when flushing normally with the water dropping down from the tank.

Make sense, or am I nuts? Never has so much been said about a bubble.

Well, it's fixed!!!!

Went to Expo and got a new bowl. No hassle. Brought the letter from
Kohler authorizing a new bowl under warranty. Hooked it up today and voila -- no more boiling frogman bubbles.

Took a hard look at the old toilet when I had everything apart and I discovered the problem. Right in the indentation for the tank gasket, where the tank dumps the water into the bowl, there was a fine hairline casting crack which was allowing air to get into the main jet channel. This toilet should never have passed Kohler's "quality control" inspection.

While reinstalling the tank on the new bowl, I popped in a Korky Max Flush flush valve to replace the Kohler half-a-flush-at-a-time valve. Now I get a nice strong full flush and no bubbles.