Main jet size needed

i bought a dellorto shbc 19 19 carb the main jet in it is a 73! when everything is put in the scooter idels well as soon as i drive it starts to jump on me so then i pull the air and it runs better! my question is what sized jet could i use to replace the one thats in it right now so that my vespa runs better??

also the vespa is kitted with a 70cc kit!

alright i tryed a few jets i had around the house! i put in a 92 jet size and the vespa runs alot better then it did ! but still on 3gear and fully open throtul the vespa starts to lose power. i also noticed i have some gas coming out of the air filter?? iv changed the original for a sport malossi filter?? any clue as to what the problem is?


should i just sell this set up and get a new one?? please help i dont wanna lose another summer with ou driving my vespa

Hi dude


Can you tell me what cylinder and crankshaft exactly do you got ?




Hi dude


a 72 seems very small to me !

Just to give you the right support:


What setup do you got regarding exhaust, ignition, manifold, rotary or reedvalve and carburetor ?




Hi dude


I guess the best would be to check out with 82 - 80 - 78 mainjet size, beginning from the highest.

The sparkplug should be a W4AC and the ignition timing 17 degrees.




92 is too large! you have been told to put a so and then, if there are still problems, we will solve them.

so i should go bigger then 73 main jet size? i thought 73 was already too big thats why the scooter was chocking?? ill try it out hope it works i dont wanna miss another session with out my vespa!



hi i have a DR 70cc kit with a stock spec mazzu crank shaft it was replaced because the original was broken!

its a 70cc with banana pipe ignition is original ,rotary! carb is a 19/19 dellortto intake is an intake from a primavera to fit the 19/19 carb


If you're riding a Smallframe 50cc Vespa with a 75cc kit, the 19/19 carb should be jetted approx 80-82.