Keihin CRs on my cb750

What I've got goin is...
81 cb750c
Keihin cr29s
K&N pods
Cycle-x 4-2-1 race system pipes.(very open)

Bike runs great till about three quarter throttle, then starts bogging, then at full it will just about kill itself.
Before I start doin plug drops and ordering jets and needles I'll ask this.
My mains are at 130 right now. What's a good starting point with jets and needle position?

I know all the basics of carb tuning and the procedures, but I was wondering if anyone has any experience with a similar situation and similar components.

Thanks

CR carbs are pretty damn close to perfect out of the box. Sure its not something else like fuelflow or retarded timing?

Not positive about the timing. It's getting plenty of fuel. I talked to a carb guy from
cycle-x here in Wisconsin. He said it could very well be an air leak. He said spray carb cleaner around the boots while the engine is running, and see if there's an Rpm change.
We'll see.

Could very well be timing. I put a set of dynatek coils on it, but never touched the ignition plate.

1st thing with a dohc is do a charging system check then do the coil relay mod to make sure you are getting full 12 volts to the coil

or they will have high rpm problems

Those carbs will never work... good news is I have a nice set of stock carbs I'll swap em out for no charge!

Thanks for the advice cx. I'll check that when I check my timing. Yeah sounds like a pretty good deal tuna. Where you wanna meet up. I'll bring the lube.

No deal eh.

Well my recommendation is find someone that has a Dyno that can tune the bike or at least give it a run and let you know what you are looking at.
Without that it is a guessing game since the bike is running well until 3/4 throttle tells me it's not getting enough fuel at that point.

My local guy will put the bike on the Dyno and give it a run and test the fuel to air ratio for $50.00 and has a really good idea what you are looking at.
Can tell you when the bike is running lean or when it is running rich.

The reason I come up with this is I also have a CB750 DOHC and it has had extensive engine work and we originally started with CR31's and come to find out we could not tune the carbs enough to run the bike because they were not giving enough fuel at wide open throttle and it was starving itself. So I sold the CR31's and got a set of CR33's because we could no longer go richer on the needles so it was easier to go leaner on the CR33's.

I believe you are probably pulling way more air than the CR29's can supply fuel with the filters and the race exhaust.
I am actually using a custom hand made gas tank with dual petcocks feeding through 5/16 fuel lines to my CR's.

If you are still using that stock tank set up which is a single petcock and probably 1/4 inch line that could be another problem.

Well good luck and hope you figure it out.

Checked timing. It was a touch off, now it's perfect. Still same issue. Cklamer hard to believe I can't bump my main jets way up. They go all the way to 225 on jetsrus. I've done nothing special to the engine and the 29s are recommended for my bike with either velocity stacks or pods. I'm still thinking it's not jet related.

Get your bike checked with a air fuel ratio sniffer that will tell you very quickly what is going on

So I talked with the folks at dynoman where I bought my carbs. They asked if I've done anything to my ignition. I told them I had 3 ohm dyna coils on it. They told me I needed the 2.2 ohm coils. I bought them, installed em. Now she goes like a bat outta hell. Just thought I'd share

Really? I'm not saying you or they are wrong because it sounds plausible that the resistance was too high but did you test the primary and secondary resistance on the old coils? Did you test the caps? I personally have never seen it make that much of a difference on good coils which is why i am asking. Also, dyna coils have a high failure rate. Ive thrown so many bad dyna coils in the trash its not even funny.

Either way thank you for posting your fix, it's solved threads that really help us all learn.

I did not check any resistance on the 3 ohm coils.
They said,
"If you have the green coils they are 3 ohm and are not the correct impedance for the stock ignition. You need the gray 2.2 ohm coils for maximum energy to your plugs. Even if you have the 2.2 ohm coils the stock ignition is old and weak and was not that good when it was new."

And,
"The reason that you can run the bike up to red line slowly is there is much less cylinder pressure and you ignition can handle it, but when a large amount of fuel and air is introduced into the motor quickly you have what is called a flame out, as the ignition does not have the energy to fire the plugs. An ignition problem and a fuel delivery problem can act very much the same even on our dyno and can sometimes be hard to know which is the problem, if you do not know how to test for it however you have gone richer and leaner and there was little difference in performance so there is a 90% chance that the problem is not the carbs. You can change jets, needles, air correctors until you are blue in the face, but after installing carbs on the DOHC Honda motors since 1979 we can tell you that the ignition should be addressed first."

Eventually I'll probably throw the dyna 2000 on it. But for now I'm super happy with the performance!

Cool thank you very much for the response. Your tuner clearly knows wtf hes talking about. I still would like to see resistance test results.