Jetting assistance

Friends, I need someone to point me in the right direction, please.

I have an Italian 1984 PX125e which has been fitted with a Malossi 166 kit and a JL Hi-Torque exhaust. The crank is standard as are the clutch and gears. The ports have been enlarged and polished in the crankcase.

I have recently bought a 24mm carburettor (PX200 dell'Orto Carb) and am about to fit it to my motor.

I currently run the stock 20mm carb with a 110 main jet which runs well.

Can someone help me with the jetting for the larger carb? What sizes do I need to try? What mixer do I need?

Thankyou in advance.

In my opinion a 118 main jet is probably insufficient... Anyway get a B8 instead of b7, which is still too hot in summer

Hi, first of all, until you keep on using the 20 carb, get sure to have 160-BE3 on the main jet because if you have 140-BE5 it is not good at all and so it is if you have an idle jet which is not 48/160 or better 50/160 (in other words you need one of these). If you have 140-BE5 and you put 160-BE3 then put also a larger main jet (116 or so). With the 24 carb the only thing you have to worry about is the main jet, which is very difficult to extablish "a priori", but surely the original 116 or 118 is very pour and you risk to ruin your engine due to an excessively puor "carburation". I think you'll need a jet between 130 and 135 or even more (I have a 138 on my 187cc very kitted) so you had better to buy the jets between 130 and 140: start with the latter and if it is too "fat" decrease size step by step until the engine works pretty well and the ceramic around the electrode of the plug is brownish (neither too dark nor too bright) after you have driven at top rews for a rather long way and immediately turned the engine off (if not the plug colour refers to the minimum rew and not the maximum, which is where the main jet affects).

Now I realize that the topic was old, well I suggest not to use the 118 with the 24 carb, I bet that the plug is white and it is very dangerous...



to get the 166 cylinder running reliable with the original crank use only/min a 28mm carb like this:



its allready jetted and you dont have to do long time adjusting...


Better to have a racing crank too- gives the food what it needs






Dont answer all at once!

Anyhow since nobody seems to know, the jet that worked was the standard 118.

Hi Grandeveget, I did tune it to wor ok with the 118 main jet and the plug colour is good but the plug I'm using is a NGK B6HS which is probably too hot. I'll get a B7 this weekend and some larger main jets and try to tune it the way you mentioned.

Thanks for replying.