Kawasaki Dirt Bikes Forum

I was wondering if there is a "rule of thumb" as far as jetting once an after market pipe is installed. I have an 07 KX250 that I've installed a PC platinum 2 pipe on as well as a PC spark arrester. The PC web site has jetting specs that run pretty close to stock save for a smaller pilot jet and a slightly richer needle setting. They don't appear pipe specific, and they don't specify if the suggestions are for stock or modified bikes. Is the general trend for bikes to go richer or leaner on the main and needle settings once a pipe is installed, this is assuming the stock jetting was correct for the stock bike.  

well normally 1 or 2 circuits will need leaned out. its not pipe specific. it depends on the stock pipe almost always the stock pipe uses richer settings. and some are richer on bottom and fine on top or vice versa, it all depends on the characteristics of the stock pipe. so because all models are different, there is no general rule except that aftermarkets are leaner.

i looked at the jetting specs and normally they lean the needle too.  
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Ride 2 strokes, buy 2 strokes, save the 2 stroke.

1998 cr125
2002 cr80

Thx for responding elko6. When you said that you looked at the specs did you mean the PC ones. Am I correct in thinking that the 4th position on the needle is richer than the 3rd (stock) position? And do you know which part of throttle position the pilot jet has the most effect on.  

yeah i looked at the PC and yes 4th is richer then 3rd. it controls 1/4 to 3/4. all it does is control when the main jet kicks in. the needle sits inside this little hole and at the other end is the main jet. so when the throttle is closed the needle sits inside the hole obstructing the flow through the main jet and as the throttle is opened it pulls the needle out of the hole and allows the gas to flow through the main jet

when the throttle is closed the pilot jet allows gas to go into the engine. a smaller number pilot jet is leaner, so it will allow less gas to enter the engine.

moving the clip from 3rd to 4th moves the needle farther out of this hole so the main jet will kick in sooner.  
______________________________
Ride 2 strokes, buy 2 strokes, save the 2 stroke.

1998 cr125
2002 cr80

So the PC specs do call for a richer needle setting, weird. Do you think their specs were for a stock bike? Also with the air screw adjustment the screw controls air bleed for the first 1/4 throttle when the pilot is effectively controlling the fuel circuit, right? I also have V force 3 reed block to put in but that should'nt have an effect on the jetting should it. Thanks again for the help.  

yeah pc specs are on a stock bike and yeah your right about the air screw. and the reeds shouldnt change your jetting but there is a possibility that it could mess up the jetting but it probably wont.  
______________________________
Ride 2 strokes, buy 2 strokes, save the 2 stroke.

1998 cr125
2002 cr80

thanks for the advice it's much appreciated