XJ750 Seca starts, then won't

I have an '81 XJ750R Seca. I bought it last November and have been working on it this spring. Person I bought it from said that 2 years previous he had the carbs professionally cleaned and tuned and it ran great. Then sat for 2 years until I got it. So far I have had the carbs off a couple of times to make sure all is clean(I did clean them myself again) and bench synced. Each day that I go out to work on the bike I can turn it on, open the throttle and start it and it fires up and will continue to run as long as I have the throttle open to about 2.5K RPM. If I let it fall below that it dies. Then I can't get it to start again. No throttle, some, lots of throttle, choke on or off. Any combination it doesn't seem to matter. It will pop, but that's it. I don't have the tank on the bike, just hand filling the fuel line. I did have the tank on and the problem was still there. Any idea's would be much appreciated.

Thanks!

 

Constant starting and stopping with out riding can take a quick toll on the plugs as I found out this winter. have you tired giving them a good cleaning? They may be fuel fouling and later dry out?

 

Yeah I was thinking that. It's been at least 45 degrees when I've been working on it. Brand new plugs. If they are fouling, what should I try to stop that?

 

Not much you can do to prevent fouling when you have to work on it. The start/stop seems to foul them.

A quick check would be to get another set of plugs and when it won't start swap them out. My fuel fouled plugs looked fine but would not run -I just replaced them. Anyway at lest you will know what the issue is. Could be something else but I can't think of anything right off.