Quote:
Originally Posted by Cravin01
Well I cant seem to be able to decide if this is worth my while, I read that a 4 stroke doesn't need a power jet but it never said it wouldn't give a improvement if used.
As always Dan threw in some valuable info about the carb and I will not be decking my head but I could polish the exhaust port myself, so I thought maybe I should look at the Keihin PWK28 ...But I'm not positive going to a power jet and a slide valve will give the desired improvement over the butterfly valve in the PZ30.
Opinions please!
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You can use a power jet carb on a 4 stroke. The idea behind a power jet is a little different from a pumper style carb in how they operate. Pumpers shoot a little fuel in right when the throttle opens to help eliminate throttle response delays, giving them an almost instant throttle response, but otherwise use the traditional jetting methods.
A power jet only adds extra fuel at wide open throttle conditions. It was originally developed for 2 stroke race bikes to try and give the best of both worlds, the extra power and higher rpm capability of a leaner main jet, but with the extra fuel needed at high rpm and high load conditions where a lean main jet can cause potential harm.
On a 4 stroke application, the same basic ideas can apply. It would allow for leaner jetting for part throttle operation, but then contribute the extra fuel needed for WOT to help prevent melting a hole in the piston or other such lean fueling issues. The benefit is not as great on a 4 stroke, but still there. In Jerry's case, if he disabled the power jet on his carb. he would likely need to up the main jet one size to compensate.
You could actually add a power jet to a pumper carb if you were really feeling froggy, but that would be a total pain in the ass to tune lol.
As far as the half round flat slide on his PWK 30 and the round slide on your PZ30. The Flat slides main advantage is that they have a higher intake velocity across the jets and less turbulence. This means they tend to be much more responsive vs. a typical round slide. The exception of this is adding an Under Flow Optimizer. The Mikuni VM30 (genuine carb) that I bought for my ported head has a UFO fitted to it. Now I just have no bike to install it on.
As far as porting your head. Do it. If you see how restricted the exhaust port is with your own eyes, you would understand that even without decking the head to raise compression there would be a definite power gain from the port work. You won't suddenly be pulling power wheelies, but the motor will pull much stronger in the higher revs, where it usually starts to feel a bit flat.