The Stovebolt Site Forums The Shop Area Engine Shop Vapor Lock revisited

Having problems with vapor lock. I have never had this problem before my last fill up. I have heard of winter gas being more prone to vapor lock than summer gas. Is this true? I got a fuel discount and opted for premium on my last fill up. I usually run regular. That is when the problems started. Could it be that I got a tank full of winter gas that has caused the problem? I am pretty sure it's vapor lock because I see the gas percolating in the filter. Also, almost no gas in the glass filter when problem exists. The fuel pump and carb are also very hot to the touch when problems arise. Water temp shows 180. I can pour cool water on the fuel pump and usually get back home. Motor is a 235 with carter YF carb. Thanks, Bob

I had vapor lock issues. Electric pump with a full return system fixed it once and for all.
http://www.chuckthetruck.com/Page26.html

at the bottom.

Hey Chuck, thanks for the good advice. Great site! Do you have to dump the return into the tank, or can you just put a "T" inline aft of the pump? Thanks, Bob

Vapor lock is caused by a weak fuel pump. An electric or new mechanical pump should fix the problem.

I put a new mechanical pump on it about a month ago. Got it from NAPA. Seemed to work great up until the last fill up. Cam lobe worn? If I go with an electric pump, what psi will work best? I saw 2.5 - 4 psi and 3.5 - 5 psi pumps @ the local FLAPS. Thanks, Bob

Your theory with the winter gas is probably the problem. It is much more volatile. You might insulate the gas line from the pump to the carb. If you use the electric pump don,t go over 4 lbs.

put some wooden clothes pins on the line tween the pump and carb til you use that gas up [old flathead Ford trick in Aridzona] - also put a 160 thermostat in, 235's run better cooler

Bill

The clothes pin trick worked for me as a temporary fix on an old 57 F@&d I used to have as a kid. (smiling inside as old memories were brought back)

Bob, I ran it back into the tank so the "hot" fuel could co-mingle with the "cold" fuel in the tank before going around again. There was room in the sender flange for a 3/8" tube. Drilled a hole undersize, extruded it with a punch and socket, ran the tube through, clamped the tube to the sender bracket, then soldered it and epoxied it. No leaks, no problems.

Thanks all. I have insulated the fuel lines and tried the clothes pin trick with no luck. I think I may go the electric pump rout. This is my daily driver, so it needs to be reliable. Thanks again. Bob

Bob - you need to find out what's wrong and fix that instead of changing things - there's NO reason that a normal 235 would run that hot no matter the gas - do you have the correct [thick] insulator under the carb? and consider changing to a 160 thermostat!

Bill

Hi Bill, I have both the 160 themostat and the phenolic insulator under the carb. Would the engine run hot if the valves are too tight? I adjusted the valves a few weeks ago and they are tighter now. I set em at .008 Intake and .017 on Exhaust. Water temp doesn't get above 185 on the gauge. Hard to get it to idle well now. I just got some fresh gas in her today so we will see if that makes a difference. I went to a different station and the new gas does not have any ethenol in it. Engine seems to be getting too warm but the water temp looks ok. ???

Try advancing the timing. Premium fuel burns more slowly than regular and is less efficient in a low compression engine and can cause overheating because the the fuel is still burning at the end of the power stroke, giving the same indications as retarded timing. You are not doing your engine any favors by using any higher octane than is needed to prevent pinging. Stories of low compression engines running better on premium fuel are just BS, not physically possible.

Shipwright
I'm guessing You solved Your problems when You gassed up at another station. I also don't see a need for anything over 87 octane in these old trucks.