Modern Vespa

First off, say that seven times fast.

Then, I'll tell you what I did to sort out some persistent fuel flow issues I've been having with the GL. I assumed it was either a kinked fuel line or fuel level issues or something else physically preventing the flow.

After I replaced the fuel line with a toyo line, which is both non-kinking AND transparent, I realized that the issue was NOT that the fuel line was kinking, but that it was generating an arch which was creating an air bubble in the line in the arch where the line went up and back down into the carb.

I used a 90 degree brass nipple I had on the shelf, cut it down to the length of the original nipple, then JBWelded it in place. I expect it will be ready to test tomorrow, but am cautiously optimistic that the GL's fuel flow issues will now be resolved.

or tap into the side

Edit: OK, it pisses me off that Polini didn't think of this!

I thought about that, too, but decided to start with this approach because it's easier. If it doesn't solve it, that'll be next.

I'm sure they thought of it, they just didn't see the value because side draft large frames are a tiny market compared to...well...every other use case.

Yeah should work! Did that on mine, drilled and epoxy, solved fuel flow issues.

No need for a pump or anything like that.

Also I added a 70deg banjo and drill through the frame.

I think the total length of the hose and banjo is something like 9inches… pretty direct to carb setup.

Mines the same way, I haven't had the cajones yet to pull out press fit and put in a 90. I just don't have a reserve, which for most of my local riding is fine.

I'll be happy to ditch the pump. Just one more piece of complexity I can now avoid. I run my fuel line through the bellows hole, which is close to what you've done. I avoid the post-painting drilling that way.

And Patrick, I realized there's also an engineering reason that Polini, et. al. don't supply a horizonal nipple--the 90-degree angle means that the fuel nipple is now a lever that can be twisted and break it loose, and they probably wanted to avoid the risk (liability) of selling something with that failure mode.

Add an air bleed at the carb?

https://www.steinertractor.com/IHS5662-Fuel-Filter-Bleeder-Valve?mkwid=|pcrid||pkw||pmt||slid||pdv|c|product|IHS5662|pgrid||cpgnid|17561055818|ptaid||adtext||&gclid=CjwKCAjw5pShBhB_EiwAvmnNVyaCcgE5cSLlQLWQ0O-xw-LSvCqdC5Hn7IFP4kSN8RvvtwkS7E5jchoC93AQAvD_BwE

My fix worked great. The goal was to improve reliability and, ideally reduce complexity, so adding bits would be a Last Choice.