Some basic jetting questions

[jpdgas]

I have searched both TT and the web and have come up with a big zero on this. I am new not only to jetting, but dirtbikes in general and the carb is still a mystery to me. I know the fundamentals of jetting from reading the FAQ and other resources and I have installed a Zip-ty fuel screw and I have tuning that down. My problem: how do I access the main jet and the needle? Can I do it without taking the carb off? Looking at the manual diagram hasnt really helped me, anyone have any visual aids or a good description? Thanks in advance, 'o gurus of jetting ?

[mxsjw]

It may help if you let us know what bike you have. ?

[jpdgas]

Whoops! ? I was in a hurry when I wrote it: '04 yz250f

Thanks

[kzoo]

I took this directly from the jetting section on www.thumperfaq.com.

Main Jet-

The MJ is a small brass threaded jet with a 6mm hex end and threads on the other. You can get to it with the carburetor in place on the bike. Turn the fuel petcock OFF. Open the float bowl drain tube and allow the gas to drain out. Take off the 17mm hex nut at the very bottom of the carburetor.  A small amount of gas will pour out that is in the nut. If you feel in the middle of the hole where you pulled the nut from, you will feel the small hex nut of the MJ. A 6mm 1/4" socket can take it off. It should only be about 1/2" long. If it is over 2" long, the needle jet came out also. No problem, just put both back in together. Loosening the boots and rotating the carburetor helps.

Needle-

The needle is under the very top of the carburetor. On a WRF you will need to remove the tank and seat. There are two 3mm hex bolts on the front and back of the top cover. Clean off the top of the carburetor and the bottom of the frame above the carburetor with mineral spirits or WD40 and a rag. Take off the two hex bolts. Carefully remove the top of the carburetor. It has a rubber gasket attached so try to do this without rubbing it around too much. Looking down into the carburetor you will see the throttle slide. Twist the throttle and it will rise. In the middle of the throttle slide is a 4mm hex screw. Remove it and it will come out along with a spring and a collar. Don't loose the spring and collar. Under it is the round top of the needle. Using tweezers or needle nose pliers, gently lift it. Have someone twist the throttle to raise it up if you have trouble getting to it. Pull it out.

I have an '04 YZ250F as well and I took the seat and tank off anyway when I wanted to get to the needle just so I could make sure that I cleaned the frame above the carb so I didn't get any crud inside when I removed the top.

?

[James_Dean]

Sometimes pictures help too-

NEEDLE ACCESS FROM THE CARBURETOR TOP--

MAIN JET ACCESS FROM THE CARBURETOR BOTTOM--

[jpdgas]

Thanks guys, this cleared up a whole load of confusion for me. I owe ya one! ?

[Fallsoffalot]

Sometimes pictures help too-

MAIN JET ACCESS FROM THE CARBURETOR BOTTOM--

Thanks for the pics JD. On the bottom picture, is the little brass screw to the lhs of the float bowl the fuel screw? Is that what I replace with my Zip Ty screw??

#Thanks,

Simon.

[mxsjw]

Simon,

Yes, that would be the Fuel Screw.

Shane