Carb Leaking, couple questions for testing OFF the

I replaced my throttle cable, so I had the carbs off. The cable took a while to come back, so I just did a rough spray down of the carbs. They were running fine, so I didn't want to tear them down or make any adjustments. I pilled the bowls and the tops and slides and sprayed carb cleaner in all the passages and cleaned some sediment out of the bowls.

I put it all back together last night and started it up. It was running for a couple minutes when I noticed the fuel was leaking from the carbs. I couldn't quite see where it was coming from.

I shut it down and pulled the gas tank. I also felt the headers and the second from the left was ice cold. Also, the leak appeared to be coming from that carb and running down the left outside carb bracket.

With the tank off, I started it up again to run off what was in the bowls. Then I saw more drips. Coming from the airbox and the left exhaust pipe.

I pulled the air filter and the left, inside carb boot is the only only one wet inside the airbox.

So it seems my left/ inside carb is over flowing.

I pulled the carbs and pulled the bowl. The float moves freely and the needle sure seems to go up in the hole.

I also pulled the right/ inside carb bowl and compared them. Both appear the same.

I then sprayed carb cleaner into the fuel line, while holding both floats up. Neither allowed the liquid to drip until I let go of the floats, then BOTH allowed the liquid to flow.


I had ridden the bike a week before the initial carb removal and nothing was leaking then. I didn't turn any adjustments or anything, just opened them up and sprayed.

If I put the bowls on and just pour liquid into the fuel line, it should leak then, right? Like it doesn't need vacuum or anything to over flow if the float is indeed allowing it to over flow?

I struggled to get my 750E carbs to seal properly. Wound up replacing the float needles and carefully setting the floats using the clear tube method to measure fuel level. To do that I set the carb up on my work bench and then suspended a remote fuel tank above that level to provide constant pressure of fuel sitting above the carbs. It took a while but I was able to get the fuel level just right.

Another thing you may want to do is check your petcock to be sure it's not flowing fuel back down the vacuum line and into the carbs that way. If the back diaphragm fails that's what typically happens.

Here's a possibility.....

Am I correct in assuming your bike uses a vacuum operated petcock, and that the vacuum line from the petcock is attached to the #2 (second in from the left as you sit on the bike) carb (the one that leaks)? If so, consider this - if the diaphragm inside the petcock has a problem it's possible that fuel is flowing through the vacuum line from the petcock into the #2 carb. If so, the float, fuel level, etc. can all be perfect but the carb will still overflow. I suggest you pull the vacuum line off the petcock and see if it is wet with any fuel; it should not be. Another test would be to put a cap on the #2 carb vacuum port that normally attaches to the petcock and also cap the petcock vacuum port. That would temporarily eliminate the possibility of fuel entering the #2 carb through the vacuum line. With those 2 ports capped you could run the bike with the petcock in the "Prime" position and see if you still have carb overflow problems. If you do they are not vacuum line related. If you don't you need to rebuild or replace the petcock. Ed

I rebuilt the petcock last year, but I'll still try that.

I hate to keep putting the carbs on and off to test things. I found a somewhat simple way to put them on and off, but it's still a pain. So I'm hoping to get it licked on the bench.

And yes, Ed. That's how it's set up

If the petcock was the problem, wouldn't the tank leak sitting on the bench? Or am I wrong in that?

Possibly, but not necessarily. When the engine is running vacuum is being pulled though that line, but it the engine is off or the tank is on the bench there is no vacuum. That being the case, if the petcock is only leaking when there is vacuum it won't leak on the bench. In any case, you may want to try it since it's an easy test. Ed

Not necessarily. If vacuum is present then gone it might leak intermittently.
Steve

This is true. The problem may not always act the same since there are many variables that can affect a damaged diaphragm, weak spring, or other petcock problem. Ed

If it's float related, I should be able to gravity feed fuel on the bench and have it over flow, right?

If it is float related, and the petcock is on prime, the floats will cause overflow on the bench.

It did fill the bowls on prime, but did not over flow. I figured that maybe because the carbs sat totally dry for two weeks, maybe the seals needed some rejuvenation, so I decided to reinstall the bank.
I pulled the air box boots so the carbs would go in easier. It seemed to run fine, no drips. After 3 minutes, I sprayed water on the headers. Left, inside header wasn't as hot as the other 3.

Then after it had been off for a few minutes, I got a couple drips.

All this for changing the throttle cable.