I got a 42 pilot jet for my 400ex, and was just wondering what it exactly does. I know that it allows, rich flow, but what does it add, any power?

thanks

 

the pilot jet supplies the engine with fuel when idling

idle only

 

Idle to about 1/3 throttle.

 

then when you give it gas,,,,your accelerator pump sqirts some fuel

as the vacuum slide opens,,,fuel begins to suck thru the main jet and mix with fresh air coming in

then when you go back to zero throttle,,,,fuel is then coming thru your pilot jet (only,,,and just a little bit,,,,enough to make it idle)


By adjusting the pilot screw you are either leaning or richening the idle circuit only. (not the whole power curve)

 

so if i were to have the pilot jet screwed in all the way, the engine would die as soon as i let off the throttle?

 

yep

 

I think you mean the idle adjustment screw (the pilot jet is always screwed in all the way inside the carb)

 

There is a pilot jet and then there is an air screw (or fuel screw). The pilot jet is the brass jet inside your caruburetor and cannot be turned to adjust. It has a fixed diameter opening, and in your case its a 42... the larger the number, the more fuel it allows to flow. The air screw is on the outside of the carb.. it meters how much air goes in your engine... if you turn an air screw in, it limits the air more. And a fuel screw is on the outside of a carb and it meters how much fuel gets to the engine... turn it clockwise and it reduces the fuel and leans the mixture. The air screw and fuel screw ONLY affect idel. The pilot affects idle to 1/3 throttleish. And if you have an air screw, then you don't have fuel screw. IF you have a fuel screw, you dont have an air screw. On that atv, I believe its a fuel screw since it is in front of the bowl.

 

i am getting confused with the terms we are using. the actually 42 jet you bought is a slow jet, but everyone calls them a pilot jet. the screw on the bottom of the carb is actually called a pilot jet but we call them a fuel screw. the 42 jet you bought you turn all the way in until it lightly seats. the fuel screw is a fine tune adjustment for the 42 slow jet. we need to realize a fuel screw is NOT the same as an air screw. an air screw will be on the side of a carb usually. an air screw will control air flow. however, a fuel screw like we have controls fuel flow. the slowjet and fuel screw work from idle to maybe around 1/8 throttle is my guess. if you turn the fuel screw all the way in, it may die. if it doesn't, you will definately be running lean at idle and thus your headers would probably be glowing pretty good.

 

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