balancing keihin FCR 35mm carburators (CNW Kit)

My Keihin carburetors are out of balance (the CNW set). Maybe someone can point me in the right direction for help.

Here is the low down. My gas tank had crud in it. I suspected some of the crud passed through the filters and into the carburetors. I disassembled the carbs to clean out crud. I have re-assembled carburetors and reinstalled on bike. Bike started first kick but is running rough. Left side seems to be putting out more "pop" and heat than right side.

The Sudco website says nothing about technical assistance. There is nothing on the outside of the carburetors that look like a balance adjustment. There are adjustment screws inside the float bowls but one has to remove the bowls to access them. Do you know of a way into Sudco technical assistance. Does Sudco sell a special adjustment tool and instructions?

If I need to take this to a bike shop for help I will. I live in the Orlando, FL area.

It would help to first eliminate cable slack, then balance the slides from flat bottom to rise at the same time.

A set of balance stix or vacuum guages, connected to the balance pipes on the manifolds, and get busy equalizing them.

Sargehopp, Unless you dissassembled the slide operating levers in the top of the carbs there should not be a reason to need to balance the slides as they are pretty much permantly adjusted as they come. If they need adjusted it is done off the bike with a drill bit to set the slides at the same height.
I would suspect that one of the low speed jets still has some crud in it. That is the small jet down in the recess that you reach after the float bowl is removed. Unscrew it and clean it with a small piece of copper wire. It's a tiny hole. Then there is an idle mixture adjustment acessable at the front edge of the float bowl. You can get to it with the float bowl in place and the bike running. It is in a deep recess and adjusted with a pocket screwdriver. In [clockwise]is leaner and out [counterclockwise] is richer. Make sure your set has a balance tube between manifolds. Some of the early kits didn't. This will make a world of difference in how those carbs work. Jim

Those of you who know the CNW keihin set will know both of the flat slides are mounted on a common spindle. The slides can be only mounted one way. You twist the throttle and both slides rise at the same time. Cable slack is not an issue.

Jim,
I did disaasemble the slide operating lever. But as I said above they can only be re-assembled one way.
The cast alloy manifolds DO NOT have balance tubes. I will look into modifying the manifolds.

Low speed jets. I did not poke any wire down there. All I have is the pressure from an aerosol can of carb cleaner. I will give the wire a try. I set the low speed jets at one and one half turns out. Is that about correct?

I did not know about the idle adjustment screw living down in a deep recess. I will look for that too. The idle adjustment is still at factory setting so I'm probably going to leave that adjustment alone for now

Thanks,
Tom

sargehopp,

I doubt many bike shops in Florida would even take a look at a Norton with Keihin carbs, let alone be able to help you. There is a shop in Melbourne, FL, Atlantic Cycle Supply, that employs an ex-AMA racer who's been around for long time. His name is John France. If you could get the bike to him he may be able to do you some good. It may pay you to become a Keihin expert. Read, read, read, ask , ask, ask.

Tom, If you dissassembled the levers they need to be readjusted.You will find a set screw with a locknut holds the lever to the shaft. The end of that setscrew is tapered and the farther it is screwed into the hole the more it lifts the slide. You will need to raise the slides about 1/4 inch using the idle speed adjusting screw and then loosen the locknuts and tighten or loosen the setscrews until the slides are the same height as measured with a drill bit under the slide. Then tighten the locknuts to keep the setscrews in position. This can be a fiddly job but once it is set it stays. If you have your old manifolds you can remove the balance tubes from them and install them into the new manifolds. It will make a set of carbs that tends to be touchy and hard to keep adjusted for a good idle into carbs that work flawlwessly. Jim

sargehopp said:

Those of you who know the CNW keihin set will know both of the flat slides are mounted on a common spindle. The slides can be only mounted one way. You twist the throttle and both slides rise at the same time. Cable slack is not an issue.

Jim,
I did disaasemble the slide operating lever. But as I said above they can only be re-assembled one way.
The cast alloy manifolds DO NOT have balance tubes. I will look into modifying the manifolds.

Low speed jets. I did not poke any wire down there. All I have is the pressure from an aerosol can of carb cleaner. I will give the wire a try. I set the low speed jets at one and one half turns out. Is that about correct?

I did not know about the idle adjustment screw living down in a deep recess. I will look for that too. The idle adjustment is still at factory setting so I'm probably going to leave that adjustment alone for now

Thanks,
Tom

Click to expand...

In response to the request for original settings, here are the settings I am using, along with the "OEM" settings as received from CNW.

The current settings are the result of a lot of experimentation over an extended period of time. Took quite a while, but these work great for me. Power, mileage, and plug appearance are all very, very good.

The FCRs are awesome carbs!

140 main jets (came with 152s)

Needle clip in #2 slot (from top; there are seven slots; the needle clips came in #5 slot I believe)

Stock pilot jets

Slow air screw out two turns (were originally out one turn)

Slow fuel screw out 5/6 turn (Right side was originally about 2/3 turn out. Left was originally 1.5 turns out)

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Brian K,

Thanks for info on the settings you use. I've been looking at the Keihin FCR expolded view. I can Identify some of the components you mention. I can identify the main jet (#27 on the parts list) and the pilot screw (#32). I think you call the pilot screw the "slow air jet".

I am having trouble figurung out what you mean by "slow fuel screw" Is this one of the slotted screws living under the spigot that mates to the rubber manifold? On the parts list these are labeled main air jet (#103) and slow air jet (#30). If so, is it the left or right screw? I have photos if this will help clear this matter up.

Tom at Sargehopp@cfl.rr.com