Oh good point Billy about the carb touching something. Might also have something in the fuel system (fuel line) sitting up against hot engine/exhaust boiling fuel and pressurizing fuel line/tank side of the float valve.

Had the same problem in some of my previous Beta's and in current one. Earlier one was cured with longer breather hose re-routed.

Current one was a bit trickier. I tried re-routing the longer hose, different versions, no succes. Then I tried without the yellow plastic part on the cap etc, even worse. Then I tried to understand what the cap is trying to do, I guess the spring actuated thing should be some kind of valve but it wasn't working right. Then I just drilled some small (1-1.5mm) holes around the plastic part, to act as a vent holes as the fuel seemed to be held in the cap by the valve thing and when it's full, it starts to spill out.

Works fine, doesnt spill fuel anymore.

Thanks again for all your interest. My mate it not a member so cannot chime in at this time. He has seen this thread and the replies and has referred them to the Beta guy here. He said Beta are sending him a modified cap, Stand by for the final outcome.

Have a good one. Taff

Beta is a great company that has bent head over heels to make me right. Explain clearly what the prob is and they will solve the issue.

It's a weird problem, and I can only think of 2 causes

Over filling the tank, expansion as the engine heats the tank and fuel

Does it still happen with a half tank of fuel?

Fuel vaporizing in the tank, vapor condensing in the hose as it cools

Is there something causing the bike to operate at a higher temp?

Is there any heat shielding that was perhaps removed or never installed from the factory

Does this bike have a hotter fuel tank than others? , one of those spaceman temp Ray guns would answer this question

OH and let's not forget, is there any modification to the bike at all?

Edited December 8, 201411 yr by 0007

Still waiting on Beta, they said they have a new fuel cap. We all, 5-6 of us, have long rides on a Sunday and all fill up our tanks but this is the only bike that leaks fuel, even other Beta's don't. The other Sunday morning 7am not hot that time of day, my mate comes to pick me up with his bike still on the back his ute and as I load mine up I point out fuel bubbling up the clear tank cap hose. Go figger????? Will get back when the cap arrives. Cheers Taff.

Waddayaknow, I'm told the cap arrived today, a flash harry red one.

Taff