20+ Miles or bust. Is my bike overheating?

I'm new to XJ bikes, and i was wondering if anyone can help me with this most interesting probelm.
I bought a 1982 xjr 750 seca a few years ago, with a parts bike for $400. With the help from a friend of mine, i picked up this bike that just needed a new battery, which after we put it in we took it out for a spin. After about 20 great Hwy miles it immediatly died and backfired instantly. After about 20-25min of trying to get it started, it finnaly started up and we proceeded back with no more problems untill about 15 mins later when it did the same thing again, so we just waited 25 min, started it back up, and finished driving back home.
Everytime that it has done that while it idoling, it idoled up to 3k than backfired & died, and if i try to start it before that time it just backfires. It almost seams to overheating which might be why it takes less and less time to die. The history of this bike is that the previous owner rewired the entire wiring harness. what the hell is goin on?

 

PM sent.

 

Steven, it sounds to me like you have a thermal issue which is common with the TCI. You might want to open it up and check the solder connections. The second culprit might be the pickup coils, which sometimes act up after heating.

 

or a plugged gas cap vent... backfiring can also mean it's running out of gas...

 

Could also be the petcock. If the rubber diaghragm is brittle and cracked it will act that way as the bike warms up for two reasons: 1) for the first 10-20 miles you are running on the fuel that has collected in the carb bowls (that's why when you let it sit for several minutes it starts and runs again because enough gas has collected in the carb bowls for the bike to run - the reason you can't run as far on the second or third starts is because you haven't waited long enough for the gas to collect in the bowls) 2) As the bike warms up the cracks in the diaghragm open up and there is no longer enough resistance for the vacuum to pull the diaghragm open to allow more gas in.

I'm with Fitz here, backfiring can mean running out of gas and that may be what is happening - I went through a similar ordeal recently. Get the rebuild kit from Chacal (it's about $25.00). And it will take you an hour to do the whole job.

 

valve clearance

 

Try to set the fuel tap on PRI. Does that make a difference? Or, with a litte precaution, prise off the fuel line - start up the engine and see if the fuel is running out (Fuel tap - ON). Collect the running fuel in a bottle.