[SlowButSteady]

It's hard to tell from you pics, but it looks like there is some sort of thermocouple unit wired into the valve assembly. Its function is to stop the fuel from flowing if the flame goes out for some reason. If it does have a thermocouple, the symptoms you describe sound like that is you problem. The thermocouple has to be hot for the valve to stay open. Your priming button over-rides the thermocouple interlock and lets enough fuel into the combustion chamber to get things going. Once it's hot the interlock should let the fuel flow at whatever rate the meter is set. But, if the thermocouple is bad, once you stop pushing the button the valve closes and that's that. If it still won't work even if the thermocouple tip is good and hot then you can change the thermocouple you'll probably be golden. Finding the right thermocouple might be a problem, however.

 

[SlowButSteady]

Thats exactly opposite how I thought it worked. I thought the thermocouple was suppose to shut off the fuel line if it got too hot. Either way, I cant imaging the thermocouple is even replaceable as I don't even know who made the unit. I assumed it was made by Bristol but it may have been manufactured for Bristol by someone else. There are no markings on the unit to be found.

Looking at the manual that Denise posted, it looks like the thermocouple works like I thought it did. Check out the trouble shooting section toward the end the the manual. You may just need to reposition the tip of the probe and/or make sure the other end is properly attached to the valve assembly.