Stalling at idle

1977 kz750b 

So new issue that started yesterday. Couple days before this on cold starts it was behaving like it was flooded (wouldn't start without cracking the throttle) Turns out my petcock was never shutting off. Fixed that issue with new O rings. 

Now when on the throttle the bike runs great. Let it idle for any length of time (at a stoplight) and it will shut off suddenly but then kicks right back over and won't happen if I blip the throttle occasionally. 

I can guarantee the carbs are clean and stock, just rebuilt them a few weeks ago. Petcock flows perfectly. Fuel filters are new. I did set the float bowl level trying to adjust for a rich running condition weeks ago but has run fine until the petcock repair. 

The only issue otherwise I know about is a leaking exhaust header on one cylinder that I am currently working on repairing to stop exhaust popping on decel. 

Any thoughts? 

If carb bowls floats valves are sealing well, the petcock passing fuel should not affect anything, as the floats would stop at the designated level....if all well.

........This is not to say petcock should not be fixed as is a backup to the floats against flooding....when engine IS NOT running.  

Intake manifold leaks.
Steve
 

So I can only assume that the floats are sealing well enough. Carbs got all new internals a few weeks ago, included floats, float valve, float seat. The bike doesn't have a center stand and seemed to be flooding the left side cylinder when sitting on the side stand overnight. I assumed due to bike not being level. I'll have to disassembly yet again to be sure. 

As for intake manifold leaks, when running I sprayed the entire area down with carb cleaner and got no change in idle at any point. Pretty sure it's not an intake leak. The only leak I have seems to be from the left cylinder exhaust header. 

 

OK, if you are sure floats valves are not passing, then fuel levels are too high.....at least one.    Being on side stand is no excuse for carb to leak.  

This is a twin, and is probably not an issue, but in the 750-4, I have made it so I can remove/replace everything in carbs from top or bottom(except enrichening plungers), w/out removing carbs from engine.   Am using allen bolts on carb bowls, and improvised some small tools.   I can adjust 4 floats and back in bike in less than an hour, if nothing else because is better take your time adjusting the float tabs.   

...............and if carbs have drain in bottom, you can always do a wet test with clear u-tube, with carbs in place.   This would test level, and verify it stops at one point.     

So I came out to the garage just now. Have done nothing since yesterday's post. I have a large puddle underneath my overflow lines. Should I assume my previous statement about floats sealing being wrong? 

Disconnected the fuel lines and verified its not flowing through the petcock 

 

If you had a manual, it should tell where the fuel level should be in the bowls.   I'd verify two things using a clear u-tube,(wet test),...... where the level is, and whether it stops at some point.  On each carb individually.   All these done with the petcock is set to prime.    This can be done with carbs in the bike.   The manual would probably tell you also what the heights of the floats should be related to carb body (dry setting)

The float valve seats can also be polished, with swab a small drill, and a bit of  metal polish.....if need be.

Am I making any sense??

.....at the very least, level is too high.....I'd say.

I'd like to start with saying thank you very much for the help so far.

After some more thorough testing it seems that one float is sticking open and allowing the carb to drain the residual fuel in the lines after the petcock. 

Lesson learned to not make assumptions, I really thought they wouldn't be dirty, but a slight tapping on the float bowl can make it start or stop leaking. To be fair the interior of my tank is pretty rusty 

No eBay APP ID and/or Cert ID defined in Kunena configurationYou can get these at any dirt bike shop.
Steve

I used to run filters with the sintered metal in them, but a couple of years ago, I ended up with four carburetors with a layer of silt in the bowls, in spite of a new filter. I now use this—-

golanproducts.com/product/super-mini-fue...r-5-16-barb-fitting/

wrote:

I used to run filters with the sintered metal in them, but a couple of years ago, I ended up with four carburetors with a layer of silt in the bowls, in spite of a new filter. I now use this—-

golanproducts.com/product/super-mini-fue...r-5-16-barb-fitting/
 

That's what I use too.  They are not cheap, but they can easily be cleaned and they will last forever.  They work!  Ed 

I know, pics or it didn’t happen.