You might have a few different issues causing that problem. First of all, propane has an oil residue in it that can build up inside of the vaporizer. There is a 10 or 12mm drain plug [can't remember for sure] on the bottom that needs to be removed when the unit is hot so this build-up called tar turns to liquid and will drain out. Wear rubber gloves and drain it on shop towels or paper towels. This liquid stinks and will soak into your skin and doesn't wash out very easy. DON'T LOSE THE PLUG IT'S METRIC THREAD!!! There is also a fine mesh screen that is under the 90 degree elbow that the fuel hose attaches to by the mixer/carb that can be plugging up with the same tar. Pull the elbow and spray it with carb cleaner or brake clean. The last thing might be a LPG fuel injector that might be bad or clogging up with the same tar. It is a round solenoid with a black rubber covering located on the top injector housing with 4 screws holding it in. One red wire and one blue wire to it and a inline 3 amp fuse in the red wire. Solenoid should test at roughly 1 olm on the connector. There is also an o-ring that seals it in the housing that sometimes can break and leak fuel past. Usually if that happens it will flood the engine with propane that you would probably hear or smell if the key is turned on. The lockoff only allows fuel to the vaporizer for about 2-3 seconds then shuts off until the engine starts. Hopefully one of these things will help solve your problem. Good Luck