TOPIC:

I have a 79 KZ 650 that I'm trying to get running consistently.  I've had the carbs cleaned, the tank cleaned and coated, new spark plugs, new petcock.  The bike will start using starting fluid and run briefly.  Occasionally, it will continue running.  Once recently it ran for ten minutes, at first using the choke and then with no choke.  What else should I be checking?   I'm far from an expert, but I have tinkered with several bikes over the years.  Any ideas are appreciated.  

If it runs then after a while stops it'll likely be one of two things. 
Fuel cap vent is blocked and as it draws fuel from the tank its creating a vacuum in the tank which stops further fuel from being delivered. Try  running with the fuel cap open and see if it resolves it. If it does clean the vent in the filler cap. 
Or coils overheating and/or pickups overheating if it has electronic ignition.

Edited to add if you have an inline fuel filter fitted with the flow direction incorrect it'll do a similar thing. 

" Runs. Then doesn't "

That's basically every bike ever.

You didn't say what type of petcock is on there. Is it vacuum-operated or gravity-fed? If it has a 'prime' setting, I would try that. It sounds like there is a small amount of fuel getting through to the carbs but not enough to keep the float bowls full. 'Prime' on a vacuum-operated petcock should allow gas to flow as if it were gravity-fed (no vacuum required). You might also try setting the petcock to 'reserve' to see if that works any better.

I don't believe this is ignition-related since it fires up on starting fluid and on fuel (sort of).

Everything mentioned makes sense to me and should be looked into.  I would also ask if you have stock carbs VM24ss with or without accel pump, and are you attempting to start/run it without any type of air filter?

New petcock with vacuum.  The carbs are stock with an accelerator pump.   Also, stock airbox with new airbox hoses.  Not trying to start it without the air filter.  

Tank coated. I’d look at the petcock area to make sure the coating isn’t restricting flow. Sounds like a fuel issue. You can make or buy an auxiliary tank, as a test procedure. 

www.chapmoto.com/bikemaster-auxiliary-fu...nt=Ad%20group%20%231

Update:  I tried the auxilliary tank idea and it worked.  Removed the tank and checked for blockages and found none.  Switched back to the original rebuilt petcock.   Now it starts on a consistent basis and is running well.   Sure is tough to start when the engine is cold!  

Thanks for the ideas!  Much appreciated!  

Sounds like the choke doesn't work.  Often times the choke pick-up tube on the carb gets plugged, or the choke fuel passage in the float bowl is blocked.  

This document is a carb rebuild tutorial, and while it's for Mikuni CV type carbs, whereas you have VM carbs, the part about testing the choke passages is the same...

gsarchive.bwringer.com/mtsac/~cliff/stor...Rebuild_Tutorial.pdf

It's now running consistently.  Part of the issue was me learning the quirks of this bike.  When to use the choke, etc.  

This morning it started almost immediately, but in checking things there is now a nice flow of gas out of the drain on the bottom right of the 
accelerator pump on carb number two.  Did a search here trying to research the issue and find nothing.  

Any suggestions?  

Try to replace the o-rings on the bowl drain screw.
If it didn´t help, next step is to replace all gasket parts of the accelerator pump system.

 

Just to clarify.  Here is where the gas is draining. 
Will the rebuilt kit solve this draining issue?  

  

This is the overflow tube. You have to set the correct bowl fuel high and check the needle valve parts aren´t damaged, clogged and moving free.