I have a 1990 Mercedes Benz 300sl the problem is that when setting all nigth and go to start the next day it starts find but when I shut off to go some wear and come out to restart it startup but den shut down like it not getting enough fuel to stay running but if I keep foot on gas panel it will stay running could this be some kind of vapor problem that it drying out by setting over nigth and should I get it put on a diagnotic machine.