Px125 questions

Hi all
I have an '86 px125e, on which I’ve bolted a malossi 166 kit and a simmeoni exhaust, everything else is standerd apart from the jets that came with the kit which I whacked in also. Everythings fine really, its just about run in now and it certainly has more power than before but at low revs or when i’m travelling along at a constant speed ( say 30mph) it seems to pop and splutter rather a lot. Is this normal? It go’s fine when accelerating.
Do I need a bigger carb or different jets?
How is the gearing effected by this upgrade? The first gear seems ridiculously short, I’m only in it for about 0.0000008 sec!!
I’m getting quite a lot of oil on the spark plug and when I stuck my finger in the exhaust i found oil in there, there’s also some bluey/ black smoke pumping out when idling.
I’m quite new to all this (as you’ve probably guess!!) so basically any tips to get the old girl running smooth as silk would be greatly appreciated.[:smokin:] [:rotate:]

Don’t worry Dylan, I can’t talk. Its Friday night and I’m in thinking about my scooter!!

Cheers for the replys Fella’s. I guess you know what I’ll be doing the weekend!
I’'ll have a look at my jet sizes…maybe put my old one back in? and maybe I’ll have a go at that thing you were talking about Dylan…sounds a bit aggresive though…not sure my neighbours would appreciate it!

Have a good one

[:drink:] [:smokin:]


well I’m not an expert but if there are wet oily deposits on your spark plug and in the exhaust it is most likely caused by oil leakage past piston rings or excess oil lubricant ( you may be mixing to much oil )…

That’s all I can say…I’m sure other guys here will be more helpfull…


I agree with Dylan, If you are talking about the mixture screw (the one on the side) it should defo not be screwed right in. I’m surprised it runs at all [:rolleyes:]

What is the main jet? What was the original?


Yes, try a smaller main jet as suggested. Going from 100 to 115 is a big difference… try 110 or 108. Be careful though, keep an eye on the plug and look for the ultimate light chocolate colour…if it starts to look white you’ve gone too low and risk burning a hole it the top of the piston.


hi runtocks
im doin the same conversion and as far as i no the jetting supplied with the kit is for when you have the crank and engine cases done.i may be wrong…this means that the motor will run far too rich.are you running standard carb?if you are ive bin told to use a 106-108 main jet.thats just what ive bin told.if your mix screw is all the way inthe bike should go like a bag of …ive bin told to use a 24 carb from a p2.im still tryin to get info on this myself.hope this is of some help.if you get any more ans give me a shout

My mate has a new px 125 and has fitted a 166 malossi and a simonini pipe, after a lot jet swapping he has settled for a 115 main jet and BE4 mixer on the standard SI20 carb.
He uses Silkolene Comp2 oil at 2% mix with the autolube system and has had no problems with it.

Thanks for the reply,

I hope its the latter. Its an auto-lube so if its mixing up to much oil how can I adjust it, the screw on the carb seems to be turned right in? [:smokin:] [:smokin:]

Actually I don’t think the screw is right in, its just a bit clagged up.

As for the jet sizes they are 160/ BE4/ 115 and 52/ 140 (these came with the kit)
The origionals were 160/ BE5/ 100 and 55/ 160.

I’ve been ragging it around all week, full throttle! ( as Dylan suggested) and the oil on the plug seems to have cleared up. Still smokes a bit from the exhaust though and it doesn’t seem to want to go much faster than 60mph, I was expecting a bit more. Any suggestions??

Cheers R.T