I can't take a picture right now, but it is number 13 in this diagram: Any idea of how I could test to see it it is leaking there?

 

Where's Waldo?

 

Maybe the carb cleaner messed it up while it was soaking?
No, it isn't snowing where I am, I am in southern california where it never snows, It is pretty nice right now, and yes it is driving me nuts!

Thanks CBR, It shall be running soon enough.

 

I think that diaphragm is the air cut off valve. It's for richening the mix under high vaccuum to the manifold.......like when you're decelerating. It keeps the exhaust from popping and chit.
It may mess with starting, I'm just not sure...... because since the intent of it is to richen the mix on decel, it would involve the idle circuit.
It may (with the choke on) suck in some air and lean it up enough not to fire?? The last thing you need is a lean condition on those carbs when you're trying to richen the mix to start it.
Just a thought.
(also, you should be able to get your hands on a rebuild kit with just the spring and diaphragm for $10-$20 or so)

Now, #13 on the other fiche (Carb assy.....the one you didn't post) shows the main diaphragm cover. If you have a leak in one of the main diaphragms (or the seal), you'll also have some problems 'cause you'll have a big vac leak. Lean again. You don't really want to get carb cleaner on any of that rubber stuff cause it can certainly dry it out and mess it up.

Also, your bike has a fuel pump, right?? Is it functioning correctly? You said two of the cylinders don't appear to be firing. Are these cylinders farthest from the fuel feed? My bike is all gravity, not sure how your bike is set up. Just another thought.

 

Thanks for the info Kilgoretrout, and yes the two carbs that aren't firing are the ones farthest from the feed but, that is a fairly new pump, just a few months so, it should still be operating properly, but I'll check it.

 

If you are getting this condition, I would switch out #1&2 pistons with #3&4 pistons and see if the the problem follows the pistons (part #18 in CBRClassic's diagram). Those piston meter fuel by allowing more as the butterfly is opened. When the butterfly is opened it causes more vacuum to pull the piston up. A tear in the rubber will cause a low vacuum and a lean mixture. When you have them out, check to see if they are all set to the same height.

These are constant velocity carbs. On mechanical carbs the needles are pulled up as the throttle is opened. In some cases under quick opening, to much fuel is pored into the carb. To correct this, a CV carb needle is lifted by what the engine vacuum calls for by sucking on the diaphragm, in turn lifting the needle.

If your #3&4 pipes are cold, the pistons may not be lifting the needles letting fuel into the carbs. You may have tears.

You may not be getting vacuum to the pistons. When you spray carb cleaner into the hole on top with the diaphragm out, you should see the cleaner spray out of the carb bore.

If the pistons don't drop properly, the mixture would be rich causing flooding and fouling. Once again, they should drop smoothly. As the piston drops it causes the diaphragm to pull air into the top of the piston through a small hole in the carb. If you have a tear in the diaphragm it will drop quickly.

Quote:

Originally Posted by pablohoney

Could having a leak or hole in that little side diaphragm be causing these problems?

I guess you are talking about the accelerator pumps. If they are mechanical types the answer may be no. If they are vacuum activated the answer would be yes as raw fuel would be sucked into the carb.

 

That's a very good suggestion TBT and I'm guessing one that should tell all too....+1

 

Sometimes if the tear or hole in the diaphragm isn't too bad you can repair it with some silicone rubber -
Even bicycle puncture repair liquid and a small piece of thin rubber...........any port in a storm ...................