Help Jetting PX 200 Polini-Reed

Hello everyone:


I'm from Spain and a good SIP client and this is the first time that I participate in this forum so I salute you all and I thank you in advance.

I'm building a PX 200 motor, with the following characteristics:


- Polini 208 two rings.

- Standard head.
- Matched casings.
- Crank modified from standard, V shape and cut.
- Timing to 18º.
- Admission matched for Malossi reed kit with Dell'Orto PHBH30 mm.
- Exhaust JL s. steel right.


The standard carb set up (low 55, needle AV 262 + x3, high 138, slide 30) is too fat.

Next I try:  low 48, AV 260 + X3 (2º clip), high 130, slide 30: I was too fat at idle (The slide?) but every thing else  was just about ok: a bit lean but got more then 130 km/h.


Next: low 50 (1 turn out mix screw- No air screw), AV 262 X3, high 130, slide 30: Too fat, but just a little better at idle. Motor hesitates going from mid to high RPM


And more, and more, and more …


Best results: slide 30, low 50 (1 turn out), Av 264 + x2 (1º clip), high 130: Idle fat and  irregular 4 strokes, good transition to mid RPM but not great, feels good at mid RPM, really bad transition to high RPM. When motor gets really hot the transition to high gets better. When it is colder out gets better to.


What should I do? Head? Slow jet? Slide? Main jet? Is the AV 264 +x2 OK?


I hope you will understand me and you will be able to help with the jetting: We are at see level.


I will be waiting for your answers.


Muchas gracias.


Yes, 125 for your polini is too small![:$](mines on a pinasco!) would have thought about 135?

wouldn't go below 40 on the slide, as when you try diffrent jets it will always change other parts that ran fine! as it always overlaps other jets/slide/needle!  

x13 is weaker than a x2 so you could try this with your av264 as it will weaken it first pulling away

 I ran mine with a polini with a standard head but modified and it ran fine, has yours been modified? if not I would get that done as squish/compresion will effect it

but this was with standard pipe/carb ran fine....but always cracked the piston!!(single ring)


The head is installed and the motor is runing much better.


50 idle jet

264 av


128-130 main

50 slide

The idle is OK, the transition is OK, the middle is ok but ..... at arround 3/4 it is a disaster [:'(], at WOT is realy fast, end less I will say.

Cheers and [B][B]


Thaks mate for your help. Nice.

It is improving, I have file the slide and it must be between 40-50. I will get it to 50.

125 main seems a bit small for my motor.

At idle 50 is ok know.

266 + x 13 seems too big, I am using 264 + x2, but I will give it a try. 

I should probably buy a head.


I'm nothing to do with SIP!!!

I would try av264

with 40 slide? yours seems very rich, but that would be just on pulling away? and might mean weaking the other parts!

mine but with pinasco barrel has

55 idle jet

266 av


125 main

40 slide

 the main tip is do ONE jet at a time!

hope this helps!


I ordered a head from SIP.... I will let you know.

hi please need help in jetting my 30mm mikuni. matched port case, mazz crank standard stroke, right hand jl pipe.

thanks in advanec. cheers!