Modern Vespa

Well I have been thinking that my P200E should run better then it does. Seems to bog down at times at WOT. I decided to order a new 118 main jet and do the air filter heart mod. Did the mod, and pulled the main jet only to find it was not the stock 116 I expected, but a lowly 109. I never bothered to check before since I assumed it was stock like everything else on the bike. I tossed on the 118 and already have gained about 5mph on the top end. I need to do a plug chop now to see how it looks, but it feels great.

Why would you put a 109 on a SI 24/24 carb?

Also, I pulled my slow jet and it is listed as an 50/120, but the stats I have seen say it should be 160/100. Should i be looking for a new slow running jet?


heading out to look at my P125X to do the heart mod on it now. Looks like my P125X has a 96 main jet, looks like I need to up-jet this a bit after the airbox heart mod, any suggestions or do a plug chop first?

This is probably redundant, but you are sure that it's a 24/24 carb, right? For a while there I think they came with 20/20 carbs.

Considering that most of these are 30 years old, it doesn't surprise me when I find a weird part substitution. Especially not on mine, it appears to have an extra iffy past.

I have seen this 2wice, once in my own '79 P200, and once again in a carb I got from a '78 P200. Both carbs are 24/24. The jetting was:

50-120
120
BE?
109

I'm running a Sito+ on the '79 with a 110 main and it goes like a champ.

Do a search here on MV. I recall another thread just like this with some good answers.

Thank mate, I did some MV searches and found all sorts of interesting info on jetting and net numbers people are using with different configs, but didn't see the thread on the 109 main jet in a 24/24 carb. I will go back and look again.

Somehow I think that the US bikes were jetted down/differently compared to Euro market. We know, for example that they were supplied with lower compression heads. Also, there was a change in the style of idle jet on the 24/24 carbs at a certain point in the run.

The online resources don't usually list all of these variations.

Don't have a source or remember exactly why I think this (other than the idle jet changes, which are in the service manual), so maybe someone with definitive info will chime in.

So since I upjetted to the 118 main, should I go ahead and upjet to the 55/160 idle jet as well as up my air and atomizer jets to the standard listed on vespamaintenance.com?

Seems there are two jetting combos used in the 24mm carb on a P200. My 78 came with the following jets:

50-120
120 / BE4 / 109

I was having problems getting rid of a part throttle stumble. I spoke to Hot Rod All and decided to switch over to the other combination:

55-160
160 / BE3 / 116

The part throttle hesitation went away and the bike felt a bit peppier with the new jets. I only had about 50 miles on the bike with the original jetting so not really sure about any deltas in top speed etc. So far I've only had the scooter up to about 60. The plug is darker though and I need to do a plug chop. A quick guess would say its richer across the board with this jet stack. I believe someone commented in an earlier post that the first jetting combo was done in order to help emissions.

Chuck

My P200 came to me with 120/BE4/109 and a 50/120 as well.

I swapped out for 55/160 and 120/BE3/160 (sito+).