(newb) How do i jet this the RIGHT way?

[nakedfrijoles]

OK, i am a newb at this stuff so bear with me, i just got a bran new HMF Slip-on for my 2002 TRX400ex. It came with the required jet, so i replaced the stock one correctly, no problem there, everything went back together fine..so now i notice 3 things happening. 1. When i am slowly creeping along in first or second gear, it wants to stall out and it starts to chug a lot more than it used to with the stock pipe. 2. There was an awful lot of black residue on the inside edge of my pipe, dunno if this is normal or not. Its not puffing black or white smoke at all.. 3. It backfires a bit excessively on decel. Sometimes its not too bad, but occasionally ill get a nice loud pop. What do you think?

[blasterandy]

It sounds like your too lean. Whats your elevation. air box lid on or off. Avrg. temp. All mods. And the current jet in the carb.

[2004exrider]

Most pipe manufactures send you a jet thats a little to big to make sure its not going to run lean. Take your airbox lid off and see if that helps with the "chugging" feeling. If it does help go to your local dealer and get a couple different jets to try out. Example: if HMF sent you a Keihin 165 then grab the next 2 sizes down, i believe its a 162 and a 158. About the sputtering on decel thats normal in most cases. You can turn the fuel screw out a 1/4 turn and that should help out. With the mods in my signature my needle is still in the stock position, fuel screw is still turned out stock (2 1/4) position, #42 pilot (stock #38) and a #165 main. I messed with the needle and fuel screw and could tell it was too rich so i set them back:confused: but every bike is different so this may or may not help you.

Jimmy

[nakedfrijoles]

Ahh, thanks alot for the help!

[northwest Texas]

I'm still doing my homework on the carbs too but I think I'm getting it figured out. I just had my engine worked on and when I got it all back together, it would hesitate slightly before acceleration. I didn't have the noise on deceleration though like you state.

What I did was to turn my fuel screw out until it quit. The jet you have should have you pretty close so adjust your fuel screw a quarter turn at a time until it stops. First, though mark it and turn it in until it lightly seats and make a note of that, beit 1.5, 2.0, 2.25 turns out.

I've been told once you get to about 3 turns out or more, a larger pilot screw is needed.

BTW, mine was lean and the reason for the hesitation was that it wasn't getting sufficient fuel.

Lets see if that helps you any.