I got myself a brand new Polini CP 17.5 carb and I read conflicting information about the air jet. Should I remove it, plug it or leave it as is for 2 stroke operation?
Top performance is cool but I aim mostly for reliability and ease of tuning.
It’s for a Polini’d V1 with reeds, but I might go back to piston port and put the reeds on another motor.
What specifically is an AirJet?
Do you mean vacuum port? Injection port?
Air jet is closed for 2 stroke applications. I believe they all come with closed air jets.
Thanks Daniel,
Mine came with a 30 jet, if I remember correctly. It's not completely closed like the one Treatland sells.
Maybe I could plug it with some solder?
> Guillaume Guite Wrote:
> -------------------------------------------------------
> Thanks Daniel,
>
> Mine came with a 30 jet, if I remember correctly. It's not completely
> closed like the one Treatland sells.
>
> Maybe I could plug it with some solder?
It sounds like maybe you are describing the Pilot Jet? Who knows, I have not touched a CP yet. Just the bigger Polini PWK's
No they are two different jets, but I think they are the same size. It's the air brake jet on the picture below.
"9. THE ATOMOZIER AND AIR BRAKE
The atomizer is a tube that connects the main jet to the venturi and it is called “two-stroke type” when it doesn’t have any hole. Otherwise if it has a series of holes along its entire length it is called “four-stroke type”.(Attention: to call the atomizers “2 or 4 stroke” is popular but technically incorrect because you can safely use atomizers with holes for the 2 stroke too. I.e the Minibikes have atomizers with “4 stroke” type holes). Its working is very easy: due to the depression in the venturi then, from the atomizer tube the liquid fuel is drawn, metered by the main jet and by the conical needle, while a certain airflow comes from the channel. Air and fuel mix together and the result is a pulverized spray sucked by the engine. To intervene in this process, in addition to the atomizer hole, there are the air channel diameter, the height of the part of the atomizer protruding into the chamber and the height of the step located in the nozzle. In addition to the atomizer’s hole diameter, the variables are therefore the diameter of the air channel, the height of the atomizer’s side that protrudes in the chamber and the “step” of the delivery nozzle. The “four stroke” type produces leaner mixture and more controlled; in fact since it is equipped with a series of holes the emulsion is done inside the tube, before the mixture reaches the nozzle in the venture. Obviously the arrangement of the holes and their diameter influences the delivery. Holes machined in the lower part of the atomizer are bathed in the fuel of the bowl so, by increasing the numbers of holes the flow of fuel increases and goes to emulsify itself with the air. The holes in the upper part of the atomizer are exposed to air and by increasing them you obtain weaker carburation at low rpm.
The POLINI CP carburetor can be adjusted so that it works with both the types, 2 or 4 stroke, changing the brake air jet.
Close air brake jet: 2 stroke atomizer type working as an atomizer without holes
Open air brake jet: the atomizer holes work and make the engine weaker."
With reeds it will work fine, the jetting will be slightly more of a pain to tune in from idle is what max experienced. He was super rich down low and thought opening the air jet up would help, but alas is just made it more rich right off of idle.
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