Modern Vespa

has anyone fabricated there own exhaust? i've lots of parts i can use, does a et4 system need back pressure or not?

cheers chris.

Chris,

Yes, you need some amount of backpressure in the system. An exhaust with no backpressure will only work well at high RPM and in the case of a CVT scooter, you are not dealing with RPMs in a very high range. Without backpressure you will get a lot of stumbling at low RPM and a rough idle.

All that said, your scooter can benefit from a decrease in backpressure up to a point. You really need to open up the intake side a bit if you want to take full advantage. And you'll need to add a bit more fuel to go along with the additional air flow. So count on a jet change (carb) or update to your fuel injection map.

-Craig

It's all limited by the cylinder head/valves on a Leader 125/150 engine unless you have access to the kind of machine shop Dynagrego apparently does in his great thread over in the Project Reports section.