Modern Vespa

Troubleshooting what appears to be a fuel starvation issue at high RPMs with my smallframe.

Before I tackle more difficult issues like pulling the tap (already cleaned carb and am probably over-jetted, as is) was wondering if someone could point me in the right direction on fuel line length.

I had it longer a while back, but it kept getting kinked between the frame and the throttle arm. Shortened it up, but now I'm wondering if it is too short (just long enough to get from tap to banjo going over top of the carb without kinking).

I know too long is such a thing, but is too short a problem too? Reading conflicting length suggestions and figured someone here might have a better idea.

Also, should I be concerned about gravity with the line running over as opposed to under the carb, or is the vaccum enough?

What about using black rubber fuel hose as opposed to the clear line?

Thanks.

bump

Too short is not a problem. And with a small frame "too long" is hardly an issue since there's really no room for it to be "too long". Mine is pretty long and actually makes a nice S curve and I've never had problems. If you're *sure* it's a fuel starvation issue and you've done everything you've mentioned above, I'd start looking at the tap next.

any auto shop has fuel line by the ft... get some extra

clear lines seem to get brittle with time due to ethanol = use the black stuff

vacuum isn't how gas get to these carbs
gravity does the work for you

there can be a vacuum lock that happens when the gas cap vent holes are clogged up and you have less than a 1/3rd tank of fuel. If the issue happens only with a low tank try loosening up the gas cap. If that helps right away then the issue is the gas cap = rebuild it and drill open the vent hole very slightly away from the gas tank. Clean well. Make sure that the metal fibers within the gas cap doen't get all wrapped up in your drill bit or get int the gas tank...!!

the fuel line should be as short as you can get it = I have mine just long enough so that I can leave it all attached to the carb and can remove the whole tank from the frame and set it sideways on the seat area. This lets you get to the carb a lot easier.

run the line a strait to the carb as you can and keep it all above the fuel line without any sharp bends. as you put the tank back into the frame the line might sit a bit off so use a flash light and make sure it OK

be safe

Good stuff. Thanks.