Could you all Zilla owners specify your needle settings and #'s please. I have a problem with mine running rich slow. It idles fine but start to be rich at 1/4 throttle then runs fine past 1/2 throttle. I have a 39mm keihin PJ with a stock needle...R1370n which translate to n427-48CGL I was thinking of going to a bigger needle dia. HELP PLEASE!!!

 

Norm, I'm running a 41.5 PWK so I'm not sure I can help with the right needle for the PJ.. (Seems they are a much different beast as far as tuning goes)

It almost sounds like it might be the pilot jet that's a freckle too rich? Have you tried a smaller jet?

Just a thought..

 

Yes I have. I've went down to 58 and still rich at 1/4 throttle. This is why I think that the needle might be too rich...but not sure by how much to lean it by...

 

hmm, I would still be inclined to believe it would be more in the pilot circuit since it's at 1/4 throttle.

The needle should cover more of the mid range area.

My $.02

 

theres a guide to setting up the carbs on the tech pages of duncan racings site, dont know if it will help you but might be worth a look

 

I agree that a smaller pilot seems to be in order. Have you tried dropping the needle down a notch or two (raise the clip position). The needle shouldn't be effecting the jetting much way down at 1/4 throttle but you can try it if different pilots don't help.

 

Depending on any mods your zilla might have, also the altitude, but I would agree that from 1/4 throttle to 1/2 is your pilot needle. Also make sure if you make any changes or adjustments, you do only one at a time. in other words don't change pilot and drop/raise jet at the same time.

 

Thanks for responding. it was greatly appreciated. I had been going leaner and leaner and leaner with the pilot jet until I reached #58 to try to correct the problem. It was idling SO lean that it would only idle at a very high RPM with the air screw only at 1/4 turn out. This was telling me that the pilot was too lean. So I started going back up in sizes until I had an air screw adjustment of 1 turn out and a pilot of 68. Now it starts great and Idles beautiful...but is still rich at about 1/4 throttle. This is why I was thinking about the needle being wrong. The clip is in the top groove! (leanest) The needle is a "r1370n" (n427-48cgl) I'm thinking of going to a larger taper but not sure how much? A larger taper would lean out at low RPM but would not affect the higher RPM. I am not a carb expert. I try to learn from trial and error, from what I read and from what other people tell me. I appreciate any response you can send my way!!

 

I recently fixed a problem for a friend that was fouling plugs on his RM250 (every ride!). His jetting was fine according to his pipe manufacturer. Upon disassembling his carb, I found two problems that could have resulted in a rich mixture. First off, the plunger-style choke wasn't properly installed. The outer rubber boot wasn't pushed on all the way which caused it to hold the choke just slightly open at all times. The other problem was with the plastic retainer (approx. 1/2-inch diameter or less) that holds the needle in place. A close inspection revealed that it was broke and was no longer holding the needle down tight against the slide. Therefore, the needle could bounce around while riding which created an overly rich mixture. The RM has fouled no plugs since making these fixes. I'm not sure what kind of carb was on that bike but you might want to check the above items if they apply to the PJ carb.

 

Will do THX