[G.M.]

I live in SW Florida where it's hot most of the year. I took a lot of temperatures with the laser thermometer over a long period of time almost every day under the same conditions. A hot carb don't seem to have to much effect while driving and you can get mislead into where you think the hot gas problem is. Under some weather conditions which I think humidity plays a part you can feel the venturi's of the carb get cool. But when the base of the carb gets 135 degrees this heat over comes the cooling action. The real vapor lock problem as I found is in the fuel pump. All you need to find and see the problem is a laser pointed thermometer and a low pressure gauge in the fuel line between the pump and carb. In 85 degrees and above look at the fuel pressure and pump temperature when the engine is cold started. The pump pressure is 4 lbs and the pump temperature 80. As the temperature of the pump rises the fuel pressure drops this don't take very long. When the pump temperature gets above 125 the pressure gets lower. As the pressure gets below 2 lbs the pressure fluxuates. At idle you still get enough fuel at 2 lbs but at 45 MPH there is not enough fuel and the engine gets a little rough. This is due to the time the fuel stays in the fuel pump at slow speeds or idle and gets hotter. At speeds above 55 MPH the fuel flowing through the pump from the tank cools the pump and the pressure stays up. This will be noticed on a trip on highways above 55 the engine runs good but when you slow down through town and hit a few stop signs or traffic lights is when the engine start to stall and gets worse until it won't start. At this point at first I replaced the fuel pump a number of times and later cooled it with cold water before it would run. I set my pump pressure to 4 lbs knowing the pressure drops from heat. If set at 3 lbs cold the problem would come on sooner. All of the guess's and "I thinks" don't show or solve the real problem the simple tools and a visual look at the problem shows what it is but don't fix it. I don't like electric pumps but they will over come the problem when it occurs. In hot areas I think the real solution is a return line after the fuel pump back into the fuel fill pipe to keep the fuel flowing through the pump cooling it. This return line want's to have an ID of between .100 and .125 or a drilled orfice in the fitting of the line of the ID mentioned above. Some more modern cars run the fuel line through a small tubular unit about 1 1/4" OD and 4 "s long with Freon from the air conditioner running through it to cool the fuel. G.M.