Keihin CV34 Choke Question

Finally pulled my carbs and started looking at what needs work. First thing I noticed is that the choke butterflys for carbs #1 & #2 don't line up with the butterflys for carbs #3 & #4.
This is with the choke all the way on:

Here it is with the choke all the way off:

I'm assuming that all the butterflys are supposed to be in line, but if that's not the case, someone please let me know. If there is something wrong, I thought it might be where the Left-hand choke operating shaft pushes on the Right-hand choke operating shaft, but I can't see anything wrong there:




If anyone has any ideas or sees the problem, I'd appreciate the help.

The #3 and #4 carb choke butterflies are on a separate shaft that is closed/opened via the wimpy spring. The #1 and #2 carbs use a much stronger spring and the #3 and #4 are sort of along for the ride when closing. The Keihin 34s choke shafts tend to bind just a little after someone has had them apart; and the effect is most noticeable on the 3 and 4 carbs because of the very weak return spring. You can take some needle nose pliers and pull the spring out a tad and bend over the end that hooks on the little catch on the 3/4 shaft end and loosen the screws on the butterfly plates and make sure the plates are not the cause for the binding. Take care not to strip these small 3mm screws and I would recommend some threadlocker when re-trightening.

Thanks WG, I'll give that a try.

Conclusion - I tried to loosen the screws on the butterflies....no go. There is actually a cut on the end of the screw that keeps them from moving out.

So....after opening and closing the choke several hundred times (at least three beers worth)...I took the plunge and actually bent the tab that the left hand shaft pushes against out of the way so that it then pushes against the tab that the return spring is attached too (while not making any contact with the spring). Tightened up the spring like WG suggested and WA LA.... everythings in line now. Look at the last picture I posted to make sense of what I just said :blink: . Now all the butterflies are in synch which should help things a bit

Thanks for the help.

The tips on the M3 screws that hold the choke butterfly plates are special... they are drilled/hollow for part of the way and that makes them easy to stake. In other words, someone put a flat blade punch on the end and smooshed them so they can't come out and fall into the engine while it is running. I don't like this method of mechanical lock and the special screws are not available (near as I know) so I buy M3 JIS screws with built on lockwashers (split type) and use a dab of blue Loctite on the screws. It is often helpful to chase the thread on the shaft because the thread is often a bit scratched up from backing out the staked screws. It will be VERY difficult to remove the screws without a JIS-type screwdriver as the slots on those screws are different than normal Phillips head screws.

George, what is JIS? Can the screws and screwdriver be purchased in an auto parts store or hardware store?

I'm glad someone posted this, I have the same issue with the carbs on my 750 Shaft. I took the carbs off the rack for cleaning and now the shaft binds. After numerous shots of everything slippery I could spray on the shafts and carbs, I fixed it "somewhat better" by removing one mounting screw on the rack, on carb 2 or 3...

JIS=Japanese Industrial Standard

Aren't these butterflies position what we adjust, against a vacuum gauge and bike running, when synchronizing the carbs??

And isn't the term "choke" more commonly applied, incorretly, to the carbs enrichening plungers we pulled when starting the bike cold?? and the butterflies rather refered to as "throttle"??

Post edited by: hugo, at: 2007/11/30 19:29

I don't think so Hugo....those are on the other side. When the choke is on, these restrict the air coming from the airbox or pods thus enriching the air/fuel mixture going to the engine, helping in cold starts.

I don't think so Link, with all due respect. Really. These carburators don't actually have chokes like carburated cars did.

Link I hope am helping, not confusing the issue. My bike is newer: a '91 with CV32s, but don't think they are that different. Anybody please correct me but I understand:

The so called "choke", lever or knob, really opens enrichening plungers above/behind the butterflies. These plungers open another fuel circuit from the bowls enrichening the mix.

In other words, these Keihins "chokes" enrich by "enrichening fuel" not by "choking air" like cars did, in spite of the name. THE CHOKE LEVER/KNOB IS NOT CONNECTED TO THE BUTTERFLIES. IT IS CONNECTED TO THE ENRICHENING PLUNGERS.

THE THROTTLE CABLE IS CONNECTED TO THE BUTTERFLIES. When you open the throttle, butterflies open and vacuum from pistons, proportional to engine demand, admits more air and lift the needle diaphragms which in turn allows more fuel in, and so it goes.