Modded 300ex jetting help!!!!!!!

[riley1374]

Need help jetting my bike. 300ex 11:1, stock carb, port & polish, big cam, HD valve springs, fmf Q series full exhaust. Below is what i have tried so far:

1) 155 main/ 38 Pilot 2 1/2 out on screw, needle clip 2nd from bottom-RESULTS
Backfired on deceleration 1/8 Throttle but rev'd ok

2) 140 main/ 42 pilot 1 1/2 out on screw, needle 2nd from bottom-Results
Wouldnt rev at all, it would idle but nothing above that

3) 155 main/a 42 pilot 1 1/2 out on screw, needle 2nd from bottom- Results same as above.

4) 155 main/ 38 pilot 3 out on screw, needle 3rd from bottom. Results- Rev'd great glowing header and high idle(couldnt get idle to come down at all)

5) 140 main/ 38 pilot 3 out on screw, needle 3rd from bottom,
Results- Rev'd great thru entire range but glowing header and backfire on decelaration on mid to low rpms.

Please help!!!!!!!!!!!!!!

[hardkoratvmxr]

try a 142 main 38 pilot 3 out on screw, needle 3rd from bottom

[riley1374]

ttt

[2muchquad]

a 155 is way too big,im running a 158 or so with a 385 kit.

[riley1374]

I tried the 42 pilot 1 turn out on mixture screw with needle clip in second position from bottom, 140 main and its running much better. Still pops on deceleration a little bit, but i think if i turn the screw out another 1/2 turn i think i may have it. Any other suggestions are greatly appreciated.

[kc8pnd]

riley1374, I am in the same boat as you, just wondering if you found the right jetting? I am about to place an order for some jets. 130, 132, 135, 138, 140 Keihin main jets. 40, 42 pilots. my dynojet kit let me down, 128 is as big as it goes and it runs like crap, cuts out big time at the top and has no where near the power it should.

[2muchquad]

if you have a stock bore 300 with just a exhaust system,i think even a 128main in the dyno jet kit would be too big.try a 122 from the kit.your probably way rich thats why it loads up at full throttle

[kc8pnd]

Stock bore, 11:1, K&N, Power 4 Core FMF with vents in air box lid. I put the 124 in it and it felt like I was riding a moped.

[Sjorge450R]

Originally posted by kc8pnd
riley1374, I am in the same boat as you, just wondering if you found the right jetting? I am about to place an order for some jets. 130, 132, 135, 138, 140 Keihin main jets. 40, 42 pilots. my dynojet kit let me down, 128 is as big as it goes and it runs like crap, cuts out big time at the top and has no where near the power it should.

do you know that they dynojets are measured different???? I have a 128 Dynojet (equivilent to like a 132ish kehin) and my quad runs great.

[kc8pnd]

hmm I thought they were like 2 sizes bigger. I will try the 128 again and mess with the mixture screw some more.