Help Needed With My Carbs Please

@KevofCov
Have you let it really heat up before revving. Also check the choke is clear. And is it getting enough fuel to feed the carbs. What i try sometimes is a tube and separate feed bottle. Really if you lay a bike up any length of time you should drain the carbs.
Joe

 

If they're CV carbs, check the diaphragms haven't perished or split.

 

Air leak issues, potentially created on re-install after your carb work ?
Will it ONLY run on full choke?

 

Look for excessive air entering the system, incorrect fitting, perished rubber connections, etc.
Can you run it with airbox/tank off?
This should show you which slide(s) are responding excessively to any slight throttle movements.

What carbs are on this?

 

This will be a time problem. Did you drain the carbs last thing before lay up. If not you have a/ 4 blocked main jets and if so your whole carb will need cleaned. To test for air leak, start bike, spray brake cleaner/ carb cleaner all around carbs/ air box. Any fluctuation in revs, is a sign of an air leak.

 

To test for air leak, start bike, spray brake cleaner/ carb cleaner all around carbs/ air box. Any fluctuation in revs, is a sign of an air leak.
Too much air is as bad as to much fuel. You need to know which it is. Is your choke an air strangulation or an add more fuel? Put your hand over the intake when running, what happens?

 

Hi, you haven't mentioned the pilot jets explicitly. Have you checked and cleaned them and the passageways to the pilot jet mixture screw?
You probably know, but I'll mention it, as I understand the pilot jet supplies most of the fuel up to approx 3,000rpm, after which the main jet (needle jet) takes over the heavy lifting (simplified, they do overlap considerably). So coming off idle the main jet won't be involved, only the pilot. When you open up the butterfly valve more air is going to be sucked in by the engine and if the pilot jets, passageways or mixture screw is blocked then the engine will most likely stall.
Apologies if I'm teaching my granny to suck eggs.
My trophy 1200 doesn't like sitting around for a few months without use. It's the carbs that always suffer.
Of course all the above comments about air leaks are also appropriate. Plus if you have the airbox off the pilot circuit is going to be running lean to start with unless you've adjusted the mixture screws.
I like this guys down to earth approach and explanations, "kev's shed" on youtube he's done some work on a sprint 900 with mikuni carbs, although the poor guy only has 3 carbs..

 

Quick way to check if the fuel head pressure is overcoming the float valves;
Using a piece of string fasten your temporary fuel tank at a more suitable height.
When I was balancing some carbs last week, my service fuel tank was suspended from a truss screw at around mirror height and all worked well including the petrol tap being within reach.

 

I am wondering if the problem is fuel at all. You say the problem affects all 4 cylinders. Each cylinder has it's own carb. Could be ignition, but if it is, I would guess it to be the primary side of the ignition [12v]. That is because all cylinders share that part of the ignition. Happy hunting. ...J.D.

 

Just a thought after rereading your thread and it's a while since I've played with vacuum carbs with problems like this.
Is the tap on the proper tank in the PRIME position?

In effect you supplying fuel from another receptacle would give the same condition, doesn't cv carbs require a vacuum tap feed of fuel i.e. no vacuum no fuel flow?
As I recall, probably 30 years ago, there's a vacuum hose to the petrol tap to facilitate the above; is that how your tank connections are?

 

My experience with Mikuni carbs was with my 95' Sprint 900. One thing I remember is on Mikuni's the needle height has an effect on the transition from idle to main jet. This can be adjusted by moving the needle up a notch or two for richer, down for leaner. Many years ago, after rejetting mine for a different exhaust, I had to set mine UP to keep it from stumbling when I opened the throttle. Might check and see where they are positioned. ...J.D.