View Full Version : cycle x dual carb setup

09-08-2009, 1:27 PM
so ive had these dual carbs since ive owned my cb750, and for the life of me, we cant get these things dialed in just right.

we started off with how it was originally set up. running open velocity stacks, had 30 pilots, 240 mains, and needle was in the middle position. we thought it was running too rich, so we went all the way down to 20s to no avail. then it was running lean. every time we bumped down a size, turning the air/fuel screw both ways, no stumble either way.

switched out the velocity stacks for smooth air filters. noticeable loss of air, still running lean. bumped up to 22.5, then 25, still nothing, but according to cycle x, thats where they should be. went all the way up to 30s hoping to come back down to 27.5s or something. still, air/fuel screw doesnt cause it to stumble.

also, all the wiring has been gone through, points checked, regapped, valve clearances checked and regapped. float arms checked for height, adjusted accordingly.

it has erradic idle, but otherwise runs fine at speed.

im wondering if the needle size is something that can also be changed? needle position has been in the middle, but have checked every position hoping that would cure something. so far, nothing is getting it perfectly dialed in.

carbs have been sync'd, both slides are opening up at exactly the same time, same gap on each, nothing seems to be sticking.

all my friends are at a loss on what it will take to get these things tuned perfectly, so any insight would be very very much appreciated. hopefully someone knows the answers to my last little hiccup keeping me from utter confidence in my bike. ill still ride it, i just would prefer it to be as little error as possible. this air screw thing is the last thorn in my side.

09-08-2009, 2:40 PM
I'm running these too, I found that changing the needle tube helped a bit. I'm still dialing mine in for what it's worth. These seem to be a little tempermental to get dialed in, but when they are running well, they really make the bike scream.

09-08-2009, 7:22 PM
Give Ken a call. Is it a tight motor with electronis ignition? I have that set up on my white bike and it rules. - Duane

09-08-2009, 7:52 PM
Hey Jake, I say we jump the pilot jet up to 35 and see if we can get it to run richer at idle cause we are turning the af screws all the way in which is full rich and cant kill it or get it to stumble which tells me it could take more fuel at idle.

I still have your jet selection.

09-08-2009, 9:09 PM
eric, im thinking the same thing, maybe even putting the velocity stacks back on, but then we may have to go higher in jet sizes...

also, i ordered my electronic ignition today. that should be here soon, hopefully mailed out today, with new throttle body and cable.

we will get this shit figured out for real!

09-09-2009, 8:35 AM
I second Ballard...Ken has helped me tremendously on mine and he doesn't mind either. Great guys out there. I would recommend their power arc ignition over the dyna b/c of the optical tooth set-up...I'm running it and it cleared out ALL of my ignition issues.

09-10-2009, 12:51 AM
see, the thing about ken, hes very helpful, getting him on the phone is almost impossible for me. he even said he needed to think about what it could be. so where do you go when even the expert is stumped?

duane, if you could crack one of your carbs open and tell me what pilot jet youre running, i think thats all i would need.

ken also said something about a vented gas cap being a possibility?

09-11-2009, 11:06 AM
I agree with the other guys, get ken on the phone. He had mine dialed in almost perfect. He "thought about it" for a day, I called him back, he had me try a few things, including moving the needle clip. I moved the clip one notch and it ran PERFECT. Ken really is a stand up guy and will help get them dialed in. He is usually there later in the day, till 9PM or so usually.

09-11-2009, 12:31 PM
yeah, i need to call him back. ive moved that needle up and down and this way, and that way, to no avail. im wondering if i need to go up in pilot size still. if anyone knows what theyre running in their carbs, that would help a lot. im sure ill fiddle with them more once i get the ignition installed. hopefully it comes soon. i really need to get on my bike and ride the piss out of it.