I've been helping a buddy of mine with a 91 dr250. It needed a bit of maintenance as it had been sitting for about 6 months. I disassembled and cleaned the carb, re-jetted from pilot jet from 40 to 42.5 and main jet from 132.5 to 135, and put new fresh gas in the tank. Idle mixture screw at 2 turns out, new spark plug, and air filter is clean. I can get it to run after a few kicks and it will run for about 5 minutes until it warms up, but it starts to stall after that and its hard to keep running. Once it stalls it won't restart, it tries to go but just dies. If you let it cool off for about 15 minutes it will start right up. I'm thinking the valves might be a bit tight as I haven't had a chance to check them yet. The bike only has 4,000 original miles on it. I'm not sure if the previous owner ever checked them. I looked up the valve clearance specs and intake is supposed to be .002-.004 in and exhaust is supposed to be .003-.005 in. For an air cooled engine it seems rather tight to me. I'm used to my klr250 at .008-.009 in on a water cooled engine. I have notice on later dr350 models the exhaust clearance has been increased to .007-.009 in. Does this sound like a possible reason for the hard starting while the engine is hot? Thanks, Fred.