Modern Vespa

Last year I swapped my 2005 PX150 engine into my Stella hack. It was a pretty simple swap, but I did swap the Stella stator / flywheel and coil / CDI unit onto the engine as all of that wiring was present on the Stella and it seemed simpler than re-wiring the bike for a short term engine transplant.

I now have my Stella engine back in my Stella and have the PX150 engine back in the Vespa with the original Vespa stator / flywheel and Ducati blue CDI ignition unit. I set the timing so it was the same with either ignition setup.

The conundrum is that the engine ran great in the Stella, but is running crazy rich in the Vespa. It is running so rich that it will basically foul the plug if not running at high rpm and even at high rpm it will miss and not rev-out like it should. It didn't have any of these symptoms in the Stella.

The carb setup and exhaust weren't touched. The engine runs cooler in the Vespa as its not lugging around a sidecar.

I am planning to just re-jet the entire carb, but what am I missing here that is making it run like this?

is something going on with the choke/cable?

Good idea - I'll check to see if the choke is sticking or somehow being held closed.

Choke is opening completely and throttle slide is also operating as it should.

I was planning on putting a Hot Wing exhaust that was on the shelf on this anyhow, so I guess I'll do that and commence the jetting process.