1982 Maxim 550 hard to start when warmed up

I have a 1982 Maxim 550. The bike starts fine in summer or winter and runs strong while driving. The problem is when I pull over to get gas, it is so hard to restart. I've tried no choke half choke full choke, open half throttle full throttle nothing. Only when I let it set at the gas station for at least 20 minutes to cool down it will start right up again. I have checked electrical connections, sparkplugs are not showing signs of too rich or too lean, fuel filter is new. Carbs were rebuilt by bike shop 3 years ago. Any advice will be be helpful.

 

Are your valves properly adjusted?
Are you carbs synched?

A possible: Try flipping to "prime" for a couple of seconds. It could be float bowl is boiling fuel off?

 

I have the same problem, but my valves have to be checked and carbs synched so I have hope. Vapor lock is unlikey as he said it happens also when stopping for gas.
Gasoline boils at 200°C, it can't just evaporate right away.

 

there's some dirt bikes that have a "hot start" lever, to start a hot engine it's like a backwards choke, leans the mix.
how's your air filter look?

 

Sounds like valve clearances need adjustment.

 

I have a gravity feed petcock. Also I have seen some pictures of the 550 with a heat shield on the carb rack. I may try to find one ebay.

 

I had a similar problem and it turned out to be low output from my alternator. The output was not enough to handle everything while running and was drawing down the battery. I had a good battery and it would build up after a few minutes enough to turn the engine and fire the ignition. Someone suggested that I check my voltage and I found it to be low. I replaced the alternator brushes and the problem went away.

 

Also, a hot starter motor may draw more amps, making the low voltage/lack of ignition spark worse. Has anyone ever tested amp draw on the starter between a cold engine and a hot engine?

 

Well I pulled the valve cover today and checked valve clearance. You all were right on. There were three exhaust too tight at .13
and two intakes too tight at .08. Thanks for all the advise. I will let you know when it all done. Thanks again to everyone.