[Jetting Help] - ATV Riders Forums - Honda, Yamaha, Suzuki, Kawasaki, Polaris, CanAm, Arctic Cat, Kymco ATVs

Pages:1

Jetting Help
(Click here to view the original thread with full colors/images)

Posted by: tgm95

Just put a 24mm Carb on my son's 70cc DRR. Can anyone give me jetting advice for the main jet. It has a 118 main jet in it right now. The temperature where I live is average 80 degrees, and the humidity averages 81%, year round.

The other parts on the quad are a hetrick racing exhaust, uni-filter, changed the rear clutch spring (big one) to a yellow Malossi one, changed the clutch springs to the Malossi red ones, and the variator roller weights to 15x22 4grams.

Thanks in advance for any help.

Posted by: TeamNeilson

I start with the main jet.
Put a brand new plug in, and get the bike warm, then run it up to full throttle.

You should be able to hear the bike start to bobble at the top end, typically this means that the bike is running out of fuel.. Go bigger. Keep going bigger until the bobble goes away. Then switch to the plug chop to determine if you are 100% on. To plug chop, run it up to full throttle and pull the kill switch (some say to leave the throttle wide open).

Pull the plug and look at the color. If its white, you best go bigger, black and wet go smaller. The ideal is dark brown(almost black), chalky and dry.

From there, I move to the needle. I start in the middle setting and get the bike up to 1/2 throttle and listen. If you hear the bike flutter, move the pin around.. I usually do one on either side and listen to how the motor behaves on each. Once i'm happy with the sound of the motor, I set the low speed air..

Turn it all the way in (but count the turns so you have a reference point to return to if everything goes to heck). Then dial it out 1.5 turns and start the motor. Listen to the motor, it should idle nice and smooth. If it doesn't go out half turn at a time and listen to the motor, if it starts to run rough, turn back and go the other way until it starts to sound like its going to die out, then find the middle of that and you are set. If you are 2.5 turns out or more, you need to get a bigger idle jet, but it's unlikely you will.

That's how I do it.. I'm sure others will chime in.

Posted by: rider1234

Take a look at this article it should help.

http://www.g-forcepowersports.com/jettinghowto.html

Posted by: bulldogfallon

What brand carb?

General advice where I would start

105 to110 MJ

Needle? Start and middle and try adjusting

Pilot 42

Not saying that this where you need to be, but that is where I would start as a safe baseline

That pipe may want more rpms, so you may need a stiffer torque spring to help it if you find it launches soft