Modern Vespa

I'm still thinking about that A/F screw, and how having it all the way in didn't actually stop the scoot from running. That seems like a weird enough issue that it's worth really focusing on. So, since for your carbs the A/F screw when turned all the way in means no more AIR, right? So yeah, seems like air is getting in anyway. If you can determine how the air's getting in, maybe that will solve the problem?

I did some googling and found a few forums where someone had a similar issue—obviously these are different vehicles so grain of salt, etc.

Also, can you confirm that you have all the little fiddly bits installed correctly? E.g. tiny o-rings?


https://www.advrider.com/f/threads/engine-still-runs-even-when-mixture-screw-is-turned-all-the-way-in.1048552/

https://www.advrider.com/f/threads/mixture-screw-all-the-way-in.226651/

https://scootdawg.proboards.com/thread/28012/air-mixture-screw-effect-solved

https://www.vmaxforum.net/threads/unresponsive-a-f-mixture-adjustments.20915/

Sitting idle it's fine. Wide open throttle it gets red.

I'll pick up a stock filter. I have some bigger jets on the way as well.

A couple updates.

I put in a bigger main. Agent from stock 82 to a 85. Made it worse.

Put in a stock air filter. Helped a bunch. Acceleration much better but the to end is still only 30-35 mph. The air screw is still all the way in. If you back it out a half a turn, you can hear the engine drop. Feels like it's still too much air.

Feels like progress.

Thoughts.

I see that the carburetor vacuum valve (or, the slide, in other words) is scratched and I don't know whether Keihn has a special coating on it, which might be worn off in this case, and the slide maybe not move freely. My Walbro Wvf Japan has some teflon-like layer that is blown off partially. I wonder, can I still use the valve or shall I replace it?[img][/img]

Resurrecting an old thread. Since I updated last, I took it to the local dealer. They systematically went through pretty much all the same stuff as documented above over the course of several months. No difference in there performance than what I had found. I eventually ran out of options and asked them to put in a new cdi. Several months of waiting for parts and boom. Runs like a top moral of my story is when all other options are rolled out, buy the spendy part and see what happens.

well, glad to hear there was a resolution!

nest time PM me and I'll send ya a tester CDI

at least it's fixed in time to get some riding in this season too!