Friend has early 50's A25X. Original problem was it would run at an idle but die when was given throttle. Then just quit running all together. This was in 2016, I replaced the vaporizer and rebuilt the mixer and was able to get it back to where it would run at idle and then die when given throttle. Due to health issues on mine and his parts both we have just now started working on it again. So I came back to work on it to find that at some point in the time off someone changed the spark plug wire position. Remedied that and now it will start run a few seconds at a very low RPM then die. Can hold the throttle wide open when starting and it will start about the same and slowly start to pick up rpm then just fade back out. Have a full tank of fuel, I have liquid propane to the vaporizer. I did hit the button on the vaporizer while it is running and it dies instantly which tells me it probably isn't a fuel issue. I did change the spark plugs, dist cap, rotor, points and condenser. It a cast flat head 4 cylinder engine.