OK this is probably obvious but it had me stumped for 2 days, so will pass on the findings to anyone using Keihin CVK carbs.

Fitted to the car and the engine would run at slow speeds, opening the throttle resulting in a slight increase in engine speed, a lot of popping and flames. Tried all the usual adjustments to absolutely no avail, the carbs were clean and spotless and jetted by Boggs. All four carbs the same...

In desperation I pulled the carbs off, and transferred the jets into another set of carbs, re-fitted - runs perfect.

Baffled and determined to find the cause, I used a vacuum cleaner against the dried out carbs to simulate the vacuum from the engine, not one of the slides was moving, traced to, despite the fact all the diaphragms were properly seated they were not sealing against the carb caps. I smeared the edges of the diaphragms with rubber lube, which is also supposed to slightly swell the rubber, left till tonight and re-assembled, the carbs all now work perfectly...

So something to check if you experience similar problems with CV carbs.

Cheers.

Pete.

[Edited on 11/11/08 by r1_pete]

Process of elimination at it's best!!!

Reminds me of the joys of Stromberg carbs, they suffered with diaphragm problems

If you have just solved my problem you are a top man. My slides dont move alot.

Ill give this a whirl tomorrow. What engine u got them on?

They're on a 1.8 blacktop Zetec with Boggs manifold Dan.

Check the two pipes coming off a little (6mm?) plastic connecter between the two outside carbs (both sides) at the top are not blocked.

On the bike they go to the airbox. On our cars they need to be free to air or you get just what you described.

Steve

Sorry to hijack the thread, but thanks gents. This might explain my intermittent rough-running-off-idle prob, too.

I had a bit of OCD with cleaning the slides and slide-guides when I took mine off, but I think I might just check this out first.

Good post. Exact same thing happened to my ZZR1100 carbs. I took care fitting the diaphragms too. In the end filling the square section groove with lube (i used proper red rubber grease), fitting the seals then replacing the tops worked a treat.

Rough running had me stumped for a while too. Perfect afterwards.