An air valve has no effect on the idle circuit and assuming float VALVES are OK a fuel delivery issue is null and void. The gas in the bowls is what it is on shut down.I have a 88 / 1500 run good but when it get's hot I have to crack the throttle a little so it will start the next time it will start right up . I have rebuilt the.carbs no change replaced the auto fuel stop and gas cap I am thinking it's a air valve sticking has any one run Into this I have been trying to find the problem for over a year
What does it idle at, when was the last time spark plugs changed, when were the carbs synced, when started cold with choke on will it run OK around 2k RPM, does the accelerator pump shoot fuel into carbs. With engine warmed up and on center stand turn idle knob down slowly until it stalls out. It should run smoothly until it stalls and what is the RPM when it stalls or lowest it will go with no stall.
When warm a touch of the starter button engine should start right up. Not quite sure what you have written about restart. Do you need to twist throttle a couple times or just open it once a little and at what speed is the RPM now when holding throttle open and engine starts.
Got all that. Print out if needed.
edit And what is the mileage on the machine. Does the engine run smooth with no surging at idle.
edit edit And the restart problem will come on after like a fuel stop or does it take longer.