We had a similar problem on our road trip grill. It turned out that the gas line was allowing gas out of the tank to fast when first turned on so the tank thought there was a leak and turned off the gas. Replaced it with a gas line from Home Depot that uses a very small hole on the input end of the line. this prevents the rapid gas flow when you first turn on the gas and prevents the tank from thinking there's a leak and shutting off. Works perfectly now.
You must turn on the gas and wait a few seconds before lighting so the line can fill with gas. It will slowly release gas when you remove the line from the tank until the line is empty. Takes some getting used to. If you look at the tank end of your gas line and it has a large opening instead of a pin hole size opening this might be you problem.
Dave
