Keihin Cr´s breaks-up at full throttle

always had to use very small air screw opening to get (more or less...) regular idling, even less than half a turn.

I guess some people here will say that their CR's carburate perfectly in street use, but honestly, its a racing carburetor with pretty bad arrangements for low speed mixing, and on top of that, even when you sinc them for good idle, the opening mechanism doesn't open them evenly, have checked this.

best piece of advice i can give you is to do what most people running CR 0n the street do: fit a remote idle adjuster so you can play with it when stopped at the lights

of course all this is unrelated to your high speed breaking up...

I never saw any of the issues you describe with CRS carbs Turboguzzi Old, original CR's had issues like that but not the CRS. I've used them on 2 valve and 4 valve engines.

The CRS could use an accelerator pump like the RS Mikuni but then again, that's all there in the FCR units.

Whenever a situation arises where "very out of ordinary" jetting is required to make a bike run correctly, either the carbs are screwed up or there are issues with the motor. A lot of the things I see posted in forums are things that if you were actually there, standing next to the bike looking things over, you'd say WTF did you expect with all these other things that need to be fixed :huh:

Believe me, I've seen plenty of it. Everything from blocking off oil cooler connections that resulted in blow the oil filter cover right off the engine to spark plug caps that were only held on the wires by the rubber boot on the small end......

It's dam near impossible to diagnose what is wrong with a motorcycle unless you are actually standing there looking at it yourself. Sure, some things are obvious in pictures but you only have pictures of certain things......

JMO from personal experience.

Remote idler adjuster installed with Mikuni clip. Very useful and real cheap solution for this carbs on steet.
As for the big problem, bike runs well at 4th full throttle but can´t really test on 5th until going track days on March. Next week will check the ignition and starting with the improvement of the brakes for vintage racing. I will open a post about that.
Thanks a lot for the suggestions





Start up video:

I finally solved the problem, I was going crazy jetting and checking ignition
I had on bike a fuel filter and Buzz from Dynoman (where i bought the carbs) advised me than in line 2 piece aluminum fuel filters work OK if you have a fuel pump, but if not (like Cr´s) they can heat the fuel and cause vapor locking.
So i removed the fuel filter and the problem has been solved!!! then plugs were dark and fouled so i went down to 115 and now plugs are perfect: not enough gas was coming through the fuck**ng filter at full throttle!!!
With the new jetting the bike runs perfect!! like a beast!!
In summer, at 30ºC temperature:
115 main jets
YY9 needle at 4º clip
65 slow jets
3/4 air screw open
NGK B8ES
Cheers
David

Ah the simplest of things, causing the most head ache.
Got any pictures of the insides of that filter? I've never used that one. But restriction in an aftermarket filter in the gravity system is a common problem.

inside the filter

good catch! never knew those sintered metal filters flow so bad.... i always use non-cool looking clear plastic ones with paper filtering where you can also see the crap in it

leitz wrote: inside the filter

Attachment DSC01999.JPG not found

Those filters are good for catching debris, and can get a restriction easy from small pieces. Could be that it is just to restrictive anyway for your engine demands.
How clean is the Tank? Ever see any small dust like brown stuff in the float bowls? = Rust.

The tank has very little rust but the filter was almost completely clean when i removed it

holly shit am I glad I stumbled onto this post. I have a dual pingle petcock and two of those filters and the same god dam problem with the bike braking up around 6-7k then flys like a bat out of hell.

Remote idle adjuster. I want one. Is that a Keihin part? Where can I get one for my CR's

leitz wrote: Remote idler adjuster installed with Mikuni clip. Very useful and real cheap solution for this carbs on steet.
As for the big problem, bike runs well at 4th full throttle but can´t really test on 5th until going track days on March. Next week will check the ignition and starting with the improvement of the brakes for vintage racing. I will open a post about that.
Thanks a lot for the suggestions

Attachment 11.JPG not found

Start up video:

Sometimes small things make big problems. Hopefully that's the problem Peter.
Barney, ask to Mike from www.power-barn.com , i bought mine there for around $35 and $4 a Mikuni cable clip to fit it