Done Everything, Still Has Hanging Idle

Alright,
Rev the engine, every now and then it hangs up around 4k or so, doesn't happen every time.

-No air leaks, guaranteed.

-Carbs have been cleaned semi-professionally (friend runs motorcycle restoration business, took them apart, cleaned ultrasonically).

-Advancer does not stick.

-No cables binding, brand new cables.

-Idle set properly.

-Adjusted the valves a few days ago.

Could the carbs be at fault? Leaking gas into venturi from somewhere?

Could the air injection system be doing something detrimental? I guess I could try blocking the valve cover ports and see if that fixes it.

I'd check/replace the rubber vacuum plugs(the ones used for carb sync.) and then check the rubber vacuum lines.

Tried the trick of spraying carb cleaner on the hoses/lines while the engie is running? If the rpm goes up, you've found your leak.

In my experience hanging idle usually means lean. Since you're certain carbs are clean and no air leaks (on both airbox and carb holder side hopefully), you might check the fuel supply. Do you have a fuel filter installed? If so is it set to flow the right direction? Is your vacuum petcock not feeding correctly? Might need rebuilt/replaced if the diaphragm isn't functioning correctly. Or it could be something as simple as needing a new vacuum line between the petcock and carbs.

Vacuum plugs are brand new. All the vacuum hoses are brand new.

I'd like to say the carbs are completely clean, but maybe something didn't cleaned up properly? What could it be?

I've sprayed all up and down this thing, no leaks. The only place it could be leaking is where the vacuum line meets the carbs on that brass plug. But it should have been reseated properly after the cleaning.

Would incorrect float levels cause this? How can it if the slides close after blipping throttle?

anarki650 wrote:

In my experience hanging idle usually means lean.

+1 but it would help if we knew what type of carbs we are talking about. That way we can narrow it down to, Mechanical, Vacuum, Fuel delivery, Fuel supply. Also we need to know if you are using a stock air filter, or if you changed into pods. Pods will change the entire dinamics of carbs especially CV carbs. Some CVs must be quite a bit modified to work with pods at all.

Completely stock. No pods, and I believe I have VM24's.

See if you can get it to do it with cables disconnected. That will narrow it down. Sounds like something mechanical hanging up to me?

There is slack in the cables though. If it watch from the side and push on the cables, nothing is staying open, there is no tension keeping the throttle crank slightly open.

I believe what Blue is sayings..... Cables can be slack but the hang up is internal where the metal stranded cable itself is catching on the spiral jacket sleeve... Spray some lubricant down the cables and confirm...

Maybe I missed it but when it hangs on high idle, whats the position of the carb return spring mechanics?
Meaning, is it still above the stopper bolt...

OMR

Richen your idle screws by closing them all the way in and than screw them out 1/2 turn richer than they were. Make sure that you remember what the original setting was. See if it still persists after that. This is a quick way to confirm or eliminate one possibility. Since You did not tell us exactly what carbs they are I can not tell you if they are Air screws or fuel screws. This will determine weather you will turn them in by an extra half turn or turn them out by an extra half turn. someone here who has a 650CSR might enlighten us on that info.

81 csr should have vm24 with accelerator pump for stock carbs. These have the air screw on the top side of the carb.

What do the plugs look like? A lean cylinder would give you a white(ish) plug, would possibly help narrow the search to know that info. If all plugs are reading correctly I'd be inclined to agree that a throttle cable might be binding up.

On my vm24's I found the rivets that hold the cable mount bracket have become lose; making the bracket have a significant amount of play in it. This caused the idle to hang on my bike (I went through 3 cans of starter fluid looking for a vacuum leak that did not exist!)

My quick fix was a zip tie to lock the bracket in place; next time I pull the carbs for a jet change (spring) I will drill out the rivets and put a couple nut/bolts there to lock it down tightly again.