15 minutes warmup on '84 XL600R?!

I've got a '84 XL600R(dual carb) recently rebuilt(new .25mm oversize piston/ring, valve job, carbs rebuild) that is now running fine except for two things :

1. When I start it(most of the time at first kick), I have to wait at least 15 minutes before removing the choke(at 75 degree F); otherwise, it will automatically stall(lean mixture?). The only way to keep it alive with the choke off before the end of the "warmup", is to always give a little bit of throttle until it's fully warmed up.

2. If I remove the choke before the end of the "15 minutes warm-up" and it stall, it will be a real pain in the ass to restart. Sometimes, it's impossible to restart and I have to wait until it's cold to restart it. If it stall after the choke warm-up, it always start at first kick like when it's cold.

I suspect that thoses two problems are linked together... I don't know if they are the stock jets, but my jets are the following actually :

Primary carb pilot jet : # 58

Primary carb main jet : # 122

Secondary carb main jet : # 120

If I momently increase the idle speed during the warmup with the idle adjusting screw, it'll not stall, but as the engine is warming up, the idle speed will increase more and more, forcing me to compensate by unscrewing the idle screw; which is, as you guess, really annoying.

I tried to put a # 65 pilot jet and # 125 main jet on the primary carb, but it made no difference at all. So now, my question is : What could it be???

THANKS!!!

1: definately lean 2: i read that this was a common thing o n these. until rejetted.

These things are very lean from the factory but it looks like you have fattened the jets up some anyway. And, as you state, you went fatter still with no positive results. Maybe a vacuum leak between the carbs and cylinder head somewhere? Try squirting some brake clean or carb clean at that area while it's idling. If the idle speeds up or slows down you know you have a problem. Be very careful when shooting that stuff at your hot engine as it is highly flammable!

I've made another test today :

With the engine running at idle speed, I turned off the fuel tank switch to see what it'll do... I was amazed to see that the engine began to rev faster and faster, and after 10 secondes of higher rev, maybe more, the rpm went down until there was no fuel in the carbs...

Could this be a sign of a too high float level in primary carb? Could this explain my problems?

I've made another test today :

With the engine running at idle speed, I turned off the fuel tank switch to see what it'll do... I was amazed to see that the engine began to rev faster and faster, and after 10 secondes of higher rev, maybe more, the rpm went down until there was no fuel in the carbs...

Could this be a sign of a too high float level in primary carb? Could this explain my problems?

what you just did with that test there is as the rpms went higher and higher, the fuel level was dropping lower and lower, thus leaning the pilot(low speed)circuit more and more until it ran out of fuel.

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