Thanks Barry - I looked inside with a dentists mirror......
Going to drill a hole under the cap so air can escape into the overflow section....If it doesn't work, plan B (whatever that is)[X(]

 

Just a thought, if you do drill it, I suggest drilling the right side so that when its on the side stand with a full tank you get less spillage.

Also, my overflow tube is blocked and I have tried unsuccessfully to clear it with a wire probe. I may try an air hose in the spring before I put her back on the road.

 

I thought of trying that too.......blowing out any muck
Just not with the cap on or you'll spring your tank seams and end up worse off ![X(]
Good idea on the right side drilling, Griffin - didn't think of that - and I don't have a centre stand !

 

It's 15 below zero (F) out, so I'm not going out to see, but on other bikes (Suzuki's) I've had, the gas cap could be taken apart and the vents cleaned. They may have kept your cap on when they coated the tank and some of the coating got in the vent. If the gas cap vent is clear, there should be no problem.

 

I'm going to pull the cap off later - only 5AM now, been up since 3....[X(]
Cap was off the bike when the coating was done but I'll see if there's a vent, as mine's a California model (but that vent was blocked before the tank went for coating)
All else fails, I'll drill a 1mm hole on the opposite side to the overflow, in the filler neck, and it can vent that way..........
Stupid cap's a pain in the butt ![:@]

 

Yep- 2 mm drill through the top of the tank, underneath the lip of the tank filler unit.
Can't see the hole. Upper right side, where drilling would be thinnest. Stuck vacuum cleaner in tank to vent it, while drilling, in case of spark. Coated drill tip with light oil, again to reduce spark....(I've seen what happens when an empty tank explodes - NOT pretty.[X(]
BTW I found out where the original vent tube was - comes out under the lip at rear of filler cap, in the middle.
I will be fitting a plastic tube with a grommet into the hole I made, and curl the pipe up so it's against the inside top of the tank, but will still vent.This will prevent pressure causing the fuel to spurt out of the hole, if the fuel sloshes around that much...not likely, but who knows.
Any fuel that does splash out will now go down the overflow on the RHS of the filler cap, and into the small air filter from the California plumbing.
Happy bunny !
Thanks to all of you for your research efforts.
Sometimes the simplest answer works, too !