engine dies after partial warm up

[briandneville]

I pulled my vision out of the garage during a break in the rain to let it run a bit.  Started normally and ran normally for about 5 minutes then started to lose RPM, approaching stall.  Giving it throttle kept it running for a bit, but eventually it died.  Wouldn't start so I put petcock to reserve, and got it to start.  It wasn't low on fuel so I put the petcock back to ON and it ran for a while.  I left it idling and when I came back maybe 15 minutes later it had stalled.  Got it started again pretty easily, but it died again after 2-3 minutes and would not restart.  I put a different TCI unit in and tried to start it, but that didn't work; battery was pretty low and I pushed it back into the garage.

3 hours later, fully charged, I put the first TCI back in and rolled it outside and it started right up, ran for 2-3 minutes and died again.  Got it started a few minutes later,  rode it into the garage and turned it off.  Engine never got really warmed up.

It's been 3-4 weeks since it ran last, but it was running well and I've not had a problem like this before.  I don't really know where to start as it seems it could be a lot of things.  Does this sound like anything anyone has experienced and if so what did you look at?

Thanks!
 

[Walt_M.]

My first thought is dirt in the carbs and you should take care of it right away. By running it only a short time your exhaust did not get up to operating temperature and and moisture created will still be inside and feeding the rust demon.

[Ken Williams]

Insufficient fuel delivery to carbs via bad fuel pump, plugged fuel filter or plugged petcock screen are potential causes I suggest be early on the troubleshooting agenda. 

[briandneville]

Agreed Walt about getting the engine to full running temp, which was my goal but did not happen the other day.

Seems there is something going on with the petcock's vacuum system, as I was able to keep it running when it stated to die today by switching to prime.  Engine got to running temp before i had to turn it off and go to work.

I've got a new petcock I ordered last summer when rebuilding carbs and doing my paintwork.  It's not installed but that will be a winter project.

Thanks for your thoughts.  They are helpful as always.

[Walt_M.]

That was a good find and it sounds like you have it under control.

[fret not]

I agree with Walt.  There are a couple other things it COULD be: blocked breather hole in fuel cap;  and failed diaphragm in either fuel pump or petcock. 

I try to go for the easy and obvious things first.