sjh55 wrote:
If this is a percolation problem, why doesn't it do it when the bike is sitting?

It can and some guys have experienced just that. When you tune off a hot bike, the carb gets hotter. The heat build up causes the fuel in the bowl to expand and it rises out of the vent tube.

Seems that starting it causes this so wouldn't that be the added pressure from the fuel pump + a float level/needle problem instead?

The fuel before the needle seat (in the line) is pressured by the pump; the fuel in the bowl is at ambient pressure. As the fuel enters the hot bowl the drop in pressure causes the fuel to boil.

Why doesn't it come out the float bowl overflow instead of the atmosphere vent? Is there a float bowl overflow?

The gas will come out from the path of least resistance which is the vent tube.

The other thing you need to consider is the gas the you are using - winter vs summer. Winter gas is blended different that summer gas (don't know about FL) . Winter gas has a lower boiling point that summer gas. You'll see this phenomenon occur more frequently in fall and spring when you have a slow changeover in the forumulation but the temps may not cooperate, such as this winter.

Wife's calling me for breakfast, talk more later.

Doc

Thanks Doc. Once again, you enlighten me to the scientific/physics aspects which I tend to forget lately. It's been 5 yrs. since I've worked on anything due to back problems and I've forgetton pretty much everything it seems.

I don't know about Fl gas either, but if this happens once it's too much for my liking.

I checked my float level - it's ok. Guess the best thing is to run a fuel line from the overflow/vent under the frame so it dumps the gas under the bike and not on the pipes.

Back to work!

i have had the same problem but inted of it leaking out it leaked into the crank case and would wash out my oil i started turning off the petcock and the problem went away for some reason you can't leave the petcock on on the roadstar

Hey JB
Outside of when I take the tank off I never shut mine off.

Ditto to what Musky said--mine always stays on.

RK

I ended up re-setting the float and cleaning out the carb. Hasn't done it since but haven't had it out on a real hot day yet. At Star Days in Longmont this year I noticed several bikes do this on start up, it was hot that day and folks seemed to think it was ok.