I have a Nissan CPJ01A15PV that will only run if you place your hand over the air horn and cover approximately 80% of the horn. If you remove your hand it dies. I have checked the distributor vacuum advance with a manual hand vacuum pump. It doesn't leak down which leads me to believe that the diaphragm is good. I have removed the vacuum fuel lock off and replaced it with an electric one. Still no change. The LP converter has been replaced twice. Same result. The carburetor/mixer has been replaced. I can't find any source of a vacuum leak. There is a switch of some type that has a vacuum hose going to it and wires connected to it. I don't know what that switch does but I put the vacuum pump on it and a volt meter and all indications show that it is working and has no torn diaphragm in it. I am at a loss at this point. I would truly appreciate it if somebody could tell me what is wrong with this machine.