105cc kit,what jets?

Hi all 


I have bought a malossi 105cc kit to put onto a 50s motor. I will be running a stock 16:16 dellorto carberator,do jet sizes 74 main and 42 idle sound right? 


Thank you 


Hi Oscar

From what I have read, the 50s, [ V5SA1T ] came stock with a 16.16 carb with 63 main and 38 idle.

I think the standard 50 [V5A1] came with 16.10 and 52/38 jets

My 50s has a 102cc Pinasco with everything else stock and I am running a 74 main and 42 idle.

I have been advised on the smallframe forum to increase the main to 79 if I install a tuned pipe like the Faco banana


Idle is ok, for mainjet it depends on:

- exhaust

- crankshaft/rotary valve timing

- crankcase ports (original or enlarged to fit those of the new cylinder?)

- air filter

The stock carb should be 16-12 not 16-16.

If you have the stock 16-12 and you are installing the cylinder with the rest original of the above mentioned parts, mainjet coul be approx. 62, plus more or less 2 with a better exhaust.

With a 16.16 add 4 points. It's all approximate, carb setup cannot be decided "a priori", it requires trying and checking the plug electrode colour in certain conditions (don't limit yourself to try one or two jets and say "it's ok" just because the vespa runs apparently well).

If you give the precise engine setup I can try to be more precise but tests are always necessary.

Standard mainjet for stock 16-12 carb is 56-58, it is 58 in the vespa HP (=xl2) which had the most performant stock 50cc engine. Check the exact carb size you have (old 50s had 16-10) and I strongly recommend you to substitute also the exhaust. What vespa/engine is it exactly (model)?

Hi Oscar. The 50s models we often get down here in NZ were originally for the Japan market, but I have read reference to them in Europe as well.

Apart from the 16.16 as stock, they also came with different gearing, and have a longer 4th gear compared to standard 50 model, so with my 102cc, and my 14/69 primary changed to 16/69 using DRT 16 cog as direct swap, I can get about 75kmph.

Yes, wheels are 10" as standard, running 3.1x10.

Also yes, my avatar is my scooter, and I am looking at banana exhausts at the moment. Oscar, you might be able to advise...my exhaust studs are 52mm apart. Do you know is standard 50 has the same, so that a pipe like the Faco banana will fit ok, [not 56mm between studs]

Sorry Sam for Hijacking the thread.[:D]

yes 52mm is the standard for vespa 50, just get a banana for 50cc ;-) (not 125cc or more)

everything else is standard exhaust,crank and airfilter wise.

I have read that a stock 50s motor runs  stock jetting at 63 and 38,so surely 63 is to small? 

Ok, surely this model was only for abroad commerce, as in Italy does not exist, but surely corresponds, with some modifications, such as the carb size (no vespa 50 in Italy was ever made with a stock 16-16 carb), to some Italian model such as "l" "r"  "n" or "special". Is it the one I can see in your avatar? A sip road banana would be great. I think 79 mainjet is too much, I think 74 is too much either with stock exhaust, even though you run a 102cc, because you have not enlarged crankcase ports, which is not a detail, you kept the stock exhaust and all the rest; usually a 50cc engine with only a 102 plug&play requires 5-6 extra points mainjet, I guess you are running with a "fat" carburation (which is not bad for engine, especially cylinder-piston, durability) with your 74 mainjet. I would keep it also with a banana, and test (correctly) the plug electrode colour at top rews. Do you have 9" or 10" wheels? I am asking in order to give you advise to adjust your setup with longer gearing without open the whole engine, as I suppose now with stock gearing the engine is always at high rews but low speed.