Jetting Problems!

I have reached the end of the line. I have a PX150 engine with a mallossi 166 kit , cosa clutch, gearing kit and a lightened flywheel but i can`t get the farting thing to run properly. It goes fine up to about 1/2 or 3/4 throttle then it starts to chug and splutter like its getting too much fuel. I am either going to try and get the jetting sorted out on that carb or perhaps i would change it for a bigger carb. I have a PHBH30 Dellorto carb, do you think that would be any good for the engine or would it just be too big. What jetting could i use in my standard carb or what carb should i use? Which would give best performance?

Any advice would be great, thanks!!!

Hi Scooternut1,

First, to my opinion a 30PHBH is too big for your engine if its the rotary induction that you have (it could suit a valve engine but with a low jetting). The standard induction (standard inlet timing) with a 30PHBH carb, reject a big part of the fuel supplied by the carb and even more when you are at full throttle. To solve this, your engine have to rev more (more RPM mean more inlet). When the fuel is reject into the carb, your mixture becomes over rich (too much fuel) and so your engine can go higher in revs, and so on....One of my friend got a 30PHBH with a 213 Pinasco but with standard inlet and is main jet is only 110 the same as the 24-24 SI, you could imagine what your carb can do with a smaller 166 kit. For your engine with standard carb ill try a 120 main jet.

Second what kind of exhaust do you have to match your engine?

Hope it has helped.

Little Bab [:bounce:] [:bounce:] [:bounce:]

I had about the same problem, it was caused by a weak ignition.
The time for „charging“ the ignition coil gets smaller the higher the rev, i.e weaker spark at higher revs.

Fixing the standard ignition might have helped, but I changed to SIP`s electronic ignition.

/Regards Lars