Xj650 only runs when cold

1982 Xj650. Replaced fusebox with inline blade-style mini fuses, as was suggested on these forums. Soldered, heat-shrinked, then taped each joint.
Then I pulled every electrical connector that I could find, and cleaned with electrical contact cleaner and q-tips.
Pulled carbs to double-check proper placement of main and primary jets (I have a Haynes manual that I used to clean them a few weeks ago). Pulled primary adjustment screws, cleaned them, and set them all 3 turns out. bench synched butterflies before re-installing.
Now, for the fun part. Bike started and ran like a champ for the first time since I bought it. I set the idle high (1500rpm) since I havent gotten to synch them or colortune yet. The bike ran for about 60-90 seconds perfectly, then cut-out, backfired, and quit. Tried to re-start, and got nothing.
I let the bike sit for about 10-15 mins, hit the starter and it fired right back up and purred for about 60-90 seconds again, then backfired and died.
Can anybody give an idea of what else I can check here? It seems like once the electrical system gets up to operating temp, something goes haywire. I'm thinking it could possibly be the TCI, but dont know of anyone I can double check it with. PLEASE HELP! Thanks everyone!

 

Right off the top of my head, have you checked to see if you are still getting fuel into the carbs a minute or so after start up? I'm thinking your float valves aren't allowing enough fuel through to support continued operation. Could be the float valves or even the fuel petcock. It will run for a short duration (less than a minute sounds about right for fuel quantity in a bowl, especially at idle without load) and then backfires (lean condition) and won't restart right away (empty fuel bowls). 15 or so minutes later, enough fuel has trickled into the bowl to support ignition again. Sound about right to you folks?
Because your engine runs fine for the duration, I'm deducting your electrical system is fine. If you find your fuel system is performing correctly, then I would look at the solder joints on your TCI board.
I'm not a carb guru, Rick or BlueMax wear that distinction. But this should be a good starting point. Good luck.

 

That sure sounds like fuel not getting to the carbs to me too.

What setting is your fuel petcock on?

 

Sounds like fuel issu to me also. Time to pull the petcock and take a look at the spiderwebs and such blocking it up. Also do a check on the prefilter/screen the goes up into the tank. It may be partially plugged. Check the fuel line. Start at the carbs and work up to the tank. Make sure the vacuum line is also connected. I place my bets on the petcock though. Let us know what you find.

 

Hi, I had the same problem last year. It ended up in changing the engine. How stupid! Shame on me. The only reason was the carb was full of crap. Take a look at http://xjbikes.com/Forums/viewtopic/t=4 ... rt=15.html

From my experience it is allways worth to check the carb inside in case of such problems. And it' easy. And if you have done it a few times as I did you will be very fast...

You will find some more details including a mass of pics on that problem on my homepage. Well it is in german but pics are clear.

Good luck.

Regards
Ramon

 

Thanks guys. I've had the carbs fully apart twice. Cleaned out the jets with a welding torch tip cleaner and soaked everything I could in cleaner for quite awhile.

I tried switching the petcock to "prime" and it seemed to do the trick. Does the vacuum mechanism inside of them go bad, or is it just clogged up?

On a side note, I got it to run well enough to make a lap or two around my grandparents 2 acre yard, but am still having trouble with the idle mix. I am currently down to 2 turns out from bottom, but it still seems to be running rich. Is there anything else to check/adjust? Thanks!