XR 600 Twin Carbs

I have just rebuilt my bike from the frame up.

Cranks first kick, runs great, but only idles w/

choke 1/2 on. Too lean?? Jets too small now??

Any info on the jets and/or clip positions appreciated.

86' XR 600R

Bored .50 over

stock manifold

Cobra exhaust

Drilled airbox

Oversized K&N

Elevation 10 Ft

Twin 28mm carbs

Mix screw 1 1/2

I pulled the jets and found:

(2) #122 Main jets

#45 Slow jet

ANY help is appreciated.


I can't help with the proper jet sizes but if it will only run with the choke half on then for sure your problem is that it is to lean. If it runs fine up higher in the rpm range then I would think something is up with your low speed circuit. Maybe something got plugged in one of your pilot jets or perhaps look for any air leaks around the intake manifold which would lean out the bike.


Anyone else?

I'm going to help keep this one at the top. My dad has an '84 XL600 w/a 628, filter and Supertrapp that he just got put back together and running today. He has the same problem. It wont run without about 1/2 choke. I was just on here searching for info and all I came up with was one recommendation for 48/125 jets on both carbs and maybe raising the needles. Can anyone confirm? 2000-4000ft, btw.

Too lean on the low speed circuit, possible air leak, pilot jet too small, dirt or varnish clogging jets or carb passages.

My XL did that from rust migrating out of the tank. Try cleaning the idle circuits and pilots. Remember that it is easier said than done. The passages are tiny and must be blown out with compressed air. Soaking and blasting with carb cleaner generally will not do the trick. Canned air for computer cleaning is a good choice.

Check the air mixture screw....I think it should be 2- 2 1/2 turns out from seated (Counter clockwise)....The fewer turns from closed or seated the richer it will be....

I'm trying really hard not to hijack this thread, but what if the primary carb doesnt have a removeable slow jet, just a mixture screw and main jet?

I went with (2) 128 mains and cleaned the (45) slow jet again.

I cleaned some grease off the tapered air screw and

everything runs great. Gained alot more power as well.

Thanks to all who helped.

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