Modern Vespa

I understand that the pilot jet is used for the first 1/8th of the throttle, then from 1/8 to about 1/2 it's the slide cutaway and above 1/2 it's the main jet.

What about the mixer tube and the air corrector? What do they bring to the party?

Plug chops? Do I need to do a plug chop at just under 1/8 throttle, at 1/4 throttle and full throttle to check each "area" of throttle?

Is there a book on this subject (vespa specific)? I've tried reading through various forums, but this subject seems to attract more bickering than solid facts.

Mark!

Here is a link on plug chopn' that helped me:

http://incriminators.series1studio.com/plugchop.html

Gettn' more miles on your P or what? I'm close to gettn' up some $$$ for a P!

Thanks for that Jason. It says only plug chop at WOT, but surely that would only tell me if I had the main jet right, nothing about the pilot, or whether the cutaway was ok.

Got a few more miles on the new top end, but not too many. If I can be happy that I'm near with the jetting on the new carb, then I'll take another 70 mile commute on Thursday on it.

Oh shit mate...did ya get a 24/24 carb or did you always have one?

When I drilled the holes in my air filter box and put on that Pinasco pipe..hp (Hiram) said only to worry about the main jet when it came to plug chopn'. I think with the set up you have, you shouldn't have to worry too much about the pilot and or cutaway. However I'm only half way sure. PM hp, he knows whats up.

I had a 24/24E, but it had suffered years of abuse - threads half stripped, slide warped etc. So I got a 24/24G (T5) carb.

I'm running a 118/BE4 and getting a nice color plug

Then you are good to go! You comn' to scoot invasion or what? Found a place to park!

The only problem is I'm not riding WFO all the time I hope I can make it

Yeah, I think I may have said to only worry about the main jet in your case (adding the Pinasco pipe), but it shouldn't be taken as universal advice. In many setups it's worth paying close attention to the idle jet circuit, as if you are too lean there you may run the risk of seizing on overrun, as you close the throttle after an uphill blast or the like.

The thing with the Si carbs is IMO they're not as clear cut as some other designs in terms of where the idle and midrange adjustments can be isolated, so it's harder to do circuit specific plug chops. Once you have some experience it becomes more a matter of WOT plug chops and then seat of the pants adjustments for the other stuff. Others' opinions may vary, and I'd be glad to hear if anyone has had good results chopping for idle jet readings.

If you want to really dig into the Si carb and jetting, I recommend reading some of the Stellaspeed threads, as they go into great detail on mixer tubes, air correctors and the like. A quick answer to your air corrector and mixer questions would be that the AC works in conjunction with the main jet stack, and the mixer tube affects the characteristics of fuel delivery within the range (not clearly richer or leaner across the range, but rather richer or leaner at different openings of the throttle).

I've found this article to be pretty useful. It's for motorcycles, but it's really the concepts you are after rather than somebody telling you specifically what to do. Hope it helps:
http://www.thumpertalk.com/forum/showthread.php?t=412662

Thanks guys.

Funnily enough, I signed up at StellaSpeed yesterday.