Vapor lock 1 and 2

[G.M.]

There are two areas that causes vapor lock in our old Fords. I have done several years of research and found #1 the carb boiling is easy to pretty much eliminate with a 1/2" thick ventilated spacer between the intake manifold and the carb. Bob showman makes a high quality one that worked on the cars I installed them on. [email protected] or 1-610-933-6637.

VL #2 is the other problem. This causes the engine to start starving for gas in warm weather when the fuel pump temperature gets to about 135 degrees. This occurs below 55 MPH. Above 55 mph more gas is flowing through the pump and cools the pump to where there is no VL. Get below 55 and into town with a few stop lights and stop signs at very slow speed and the engine cuts of. The fuel pump needs to be cooled to get restarted.

I just finished putting a simple 3/16" steel brake line fuel return from after the fuel pump back to the filler neck in my 39. I have a fuel pressure gauge in the pump to carb line after a "T" with a needle valve from where the return line runs right after the pump. I can look in the filler neck and see the fuel returning. I can also watch the pressure gauge and see the effect of pressure to the carb as I open the needle valve returning more fuel. It looks like I want to see about 1/2 lb of pressure drop to the carb to get about the amount of return fuel I THINK I need.
Two considerations, first enough fuel at 75 MPH and second enough fuel returned to cool the pump without starving the engine. I only need a little more fuel returned than the extra fuel used between 55 and 75 MPH. I have about a 1/2 tank of the old type fuel in the tank which I have to run out before filling up with the new stuff. I know this will work and I will stick my neck out and say I can tell if it works by the outside temperature of the pump. The pump on this car runs at 135 when it's hot out and the engine gets to 180, this is about where VL starts below 55 MPH. I'm pretty sure from all the testing I have done that the pump will run down in the 125 range which is below the boiling point of the new gas.
I can tell even with the old type gas by the temperature of the pump if it's going to solve the problem with the new gas. It's going to be 85 tomorrow so we will take it for the same 30 mile run for lunch we did all the other tests on. I have a few pictures I will post over the weekend. G.M.

[ford38v8]

George, Show us the gage/needle valve setup please?
And question here: With the original 1/4" fuel line going in, isn't a 3/16" return line overkill? Is it even possible to open the needle valve all the way with the return so large? Or is your setup strictly for testing at the moment?

[G.M.]

Originally Posted by ford38v8

George, Show us the gage/needle valve setup please?
And question here: With the original 1/4" fuel line going in, isn't a 3/16" return line overkill? Is it even possible to open the needle valve all the way with the return so large? Or is your setup strictly for testing at the moment?

The steel brake tubing is 3/16" OD. I didn't measure the ID but it isn't much over 1/8" It takes about 14' so I wouldn't want anything smaller for the first test. I'm not going to change it, besides you can't support the return line very easy. The needle valve sticks out towards the wire cover below the voltage regulator. So there is about 8"s of tube heading over to upper left corner of the cover with a try wrap around the wire bundle that go's across the firewall. The tube bends down at that point and over with the fuel line. There is a screw just below there holding the wire cover on. I'll make a nice little tube bracket secured by that screw. I ran it back tie wrapped to the fuel line, between the double frame rails up over the wheel through a small hole in the bottom corner of the rear cross member coming out with a small lopping bend out under the rubber gas hose coupling. Tie wrapped to the vent pipe up to a 90 degree ferrule fitting with a short 1/8" pipe coupling brazed into the filler neck down about 5"s from the top. I can look in the filler neck and see the return fuel flow. I let a friend use the lift to install a new engine in his T Bird so I was on the floor and could only get one hand up to put the tie wraps on. Good finger practice putting tie wraps on with one hand. When I open the needle valve all the way open it gets down to about 1 lb pressure with a pretty good flow. I only ran it about 5 minutes in the shop. Going to take it to the car wash in the morning and as I said take it for a trial test run for lunch. I won't be able to go over 70 MPH but that should let me find out just how far I can open the valve and not starve for gas. I'll put the camera over by my shoes right now so I don't forget it. G.M.

[Lawrie]

George, would it not be easier to insulate the fuel pump or stand like the carb insulator, you may have to lengthen the pump push rod though.
This would seem to be a better dix than the return line setup.
I will tell you later if just the carb insulator works ,as we are off away in the 33 ,about 1000miles each way towing the caravan.
Lawrie

[G.M.]

Originally Posted by Lawrie

George, would it not be easier to insulate the fuel pump or stand like the carb insulator, you may have to lengthen the pump push rod though.
This would seem to be a better dix than the return line setup.
I will tell you later if just the carb insulator works ,as we are off away in the 33 ,about 1000miles each way towing the caravan.
Lawrie

I made a 1" insulated spacer under the pump and extended an adjustable push rod to get the exact fuel pressure I wanted which is just a little over 4 lbs. As the pump warms up the pressure drops. Also a laminated aluminum and fiber glass insulation "plate" about 6x10"s under the pump. Also computer fan over the pump with an aluminum heat sink pad off the fuel pump with a thermal switch to turn the pump on. Every thing was added one at a time to see the effects of each addition. I started at the gas tank. I have dual exhaust and at the rear corners of the tank the tail pipe is within 1" of the tank and could feel the tank getting warm. I used roof flashing aluminum 12" long and bent a "U" shaped tube with 2 ears about 1 1/2" the entire length with matching holes to clamp the tube around the pipe. This really was a good heat sink and took the heat away from the tank but didn't cool the pump. These were so effective I will leave them on. Next I moved the left fuel line (duals) to make sure is was as far from the exhaust as possible and made an aluminum baffle to fit in the frame up the entire area over the wheel. Removed this yesterday. Put rubber hose over the fuel line from the frame below the firewall to the flex hose, still no improvement of heat at the pump. Put heavy foam pipe insulation over rubber hose and flex hose right up to pump, still no improvement, removed yesterday. Made the insulated plate 6x10 under the pump, removed yesterday. Made the 1" pump and long push rod. Didn't make any change but didn't remove yet. Installed the 12 volt high speed computer fan with thermal switch over the pump with a bracket off the MMO injector. This required a large 12 volt converter to run the fan. The fan did cure the gas boiling in the pump but is to bulky and expensive as a cure. Each item installed was done then tested on the SAME trip test of about 60 miles on 85 plus temperature days. Temps were taken at the start, stop for lunch again in about a 1/2 hour after lunch and after trip back at the garage.
Everything at the rear of the engine gets to at least 135 degrees, firewall, fuel line, fuel pump with no real air circulation. I even slit rubber hose 3"s long and installed on the rear edge of the hood to try and get some circulation, sill hot.
I came to the real solution from hind sight from my trip from Florida to Penna. stopping at the EVFV8 meet in Charlotte a few years ago. It was over 100 degrees on both days of the 1,200 mile trip up I-95. It ran good at the speed I traveled 65 to 75 but when I would get off for fuel and in stop and go traffic is would stall and I had to fool with or replace the pump. One time I got into stop and go traffic on I-95 due to construction and it got real slow and the engine started running ruff. I finally pulled over on the right shoulder and went past the traffic and was going to get off I-95 but in a few miles got around the problem, back up to speed and the problem went away. I tried going slow several times and the problem came back. When a certain amount of fuel is flowing through the pump the small extra amount of fuel over 55 MPH cools the pump. This amount plus a little more back through the return line should solve the problem, today we shall see??? G.M.

[BILL WZOREK]

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G.M. Have you ever gave any thought to changing the size of the pully on the fan to speed it up to get more air flow under the hood ??

[G.M.]

I have done this plus 6 bladed industrial fans on generator mounted fans plus a shroud which is the best cooling with hi flow pumps you can get. BUT this is a 39 deluxe with the crankshaft mounted fan which only throws the air against the front of the block. G.M.

[gary635g]

Thanks to all for some very good information. I remember this a very common problem that I had on my 51 back in 1959 coming over the Siskues(sic) in Oregon I used all the cokes I had to cool the pump so had to resort to peeing into a empty coke bottle and pour on the pump to get over the mountain. Not sure what I did for long term solution perhaps a new pump and a small nut for a shim to give more stroke to the pump. Took a while to get rid of the odor of burned pee! Gary

[G.M.]

Good trip. First a little advise on getting in a hurry to tear things apart. On the test trip the engine was running crappy, I pulled the choke to try to clear it and finally in about 15 miles it took a gulp and started running pretty good. Gas is over a year old and smalls bad. Every time we slowed down we could smell it.
Before starting the trip I had 3 1/2 lbs fuel pressure and adjusted the return valve down to 2 1'2 lbs. After about 7 miles with running so bad I stopped to close the valve completely thinking I was returning to much fuel and starving the engine. Closing the valve didn't make any difference, still crappy. At about 15 miles what ever dirt was causing the problem went on by and it perked right up to as good as it will get until I run this bad gas out. Stopped for lunch and checked the top of the pump and it was 118 degrees, opened the return valve to about 2 1/4 lbs letting gas flow through the pump and back to the tank at an engine speed of about 20 MPH. The pump temperature started dropping and after about 2 minutes the pump cooled to 109 on the top. Stopped on the road a couple of times adjusting the valve/ to see if it would starve for fuel and didn't see any signs of starvation above 2 1/4 lbs of pressure. Keep in mind the engine wasn't running 100% with this old smelly gas. Got back to the shop, opened the hood and had 123 on the top of the pump. Opened the valve further with no change. Checked the temp on the bottom of the pump and it was 170. It was a little hotter on the return trip as the sun came out. It looks like it works just as I thought it would. Will do more tests when I get rid of the old smelly gas. Took some pictures of the return tube installation. Will post them when I figure out this new camera and load the pictures. G.M.

[G.M.]

Was thinking about the return fuel line and something came into my mind. It will be interesting to see if the fuel drains from the pump to carb fuel line back to the tank after sitting a while. I will find out next time I start it. IT may not effect starting if it don't drain the pump. The check valve in the pump should keep enough fuel in the tank line and the glass bowl to start. At the worst I will need a 2 lb check valve in the return line. G.M.

[ford38v8]

GM, So what i understand from your trip report is that it seems to make no difference the degree open as long as there is some constant flow back to the tank? That would make sense from your previous report that below 55 mph woiuld cause intermittent operation of the pump and excess heat build up.

On the 2 lb check valve you are presently thinking about, I think that would complicate your effort with no gain. Remember, you already have a check valve in the carb, so the effect would be to allow heat soak pressure in the pump to carb line that may overcome the carb check valve before the line check valve, not good.

[G.M.]

Originally Posted by ford38v8

GM, So what i understand from your trip report is that it seems to make no difference the degree open as long as there is some constant flow back to the tank? That would make sense from your previous report that below 55 mph woiuld cause intermittent operation of the pump and excess heat build up.

I can't pin down the exact amount of fuel that can be returned without starving for fuel on one test run, Also I'm going to have to run the old nasty smelling fuel out to get a true feeling of when there is not enough fuel at 65 to 70 MPH. The excessive fuel being returned is what will cool the pump. This was evident at the lunch stop with no fuel being returned and the temp on the top of the pump was 118 and I opened the return and the temp dropped to 109.

On the 2 lb check valve you are presently thinking about, I think that would complicate your effort with no gain. Remember, you already have a check valve in the carb, so the effect would be to allow heat soak pressure in the pump to carb line that may overcome the carb check valve before the line check valve, not good.

There is no check valve in the carb. If your referring to the needle valve if it's closed it would prevent drain back through the return line. If it is open it allows air to enter the pump to carb line and the return line letting fuel drain back through the return line. An exact check valve at 2 1/2 lbs could eliminate the needle valve. But if the check valve is not on the money at 2 1/2 lbs the return flow changes. A lower check valve at say 2 lbs would allow full return flow if desired but prevent drain back after shut down. We are getting into "what if's" and that's not my game. I am set up to get real life results. This where it takes time and patience to find the true answers. G.M.

[keith oh]

Forgive my nay-say comment but back in the mid 50s I drove my standard fuel set up 1951 ford all over Texas in over 100 deg. weather with no "vapor lock" problems. Also back and forth to Ohio a couple of times. If there is, in fact, vapor lock problems occurring now, then it must be in the formula of the fuel nowadays.

[G.M.]

The problem is with this new 10% ethanol fuel it starts to boil in the fuel pump in the 130 to 135 range. On a warm day after running awhile every thing in the area at the rear of a 39 deluxe engine gets over 135 degrees. It also boils over in the carb mostly after shut down. This can be corrected with a 1/2" vented insulator under the carb. The pump boiling is more difficult to over come. It looks like I may have finally have a sure solution but it requires installing a return line which a lot of people won't want to do. I never had any problems either until this stuff came along. We can get the old type fuel locally without ethanol but if you go on a trip who wants to search for it. I have 3/8's of tank of smelly old fuel to burn out before I can refill with new ethanol. Then I can do some tests when it's above 85 outside and get definite answers. G.M.

[ford38v8]

Originally Posted by G.M.

...An exact check valve at 2 1/2 lbs could eliminate the needle valve. ... G.M.

Hold on here. The carb is looking for the correct float level in the bowl. A pressure based check valve will not satisfy that need, only the float controlled needle valve can do that.

So... let the return line drain back to the tank if the float opens the needle valve. No problemo with that, is there? Why allow a pressure buildup in the line after shut down anyway?

[G.M.]

Originally Posted by ford38v8

Hold on here. The carb is looking for the correct float level in the bowl. A pressure based check valve will not satisfy that need, only the float controlled needle valve can do that.

Check valve is in the return line not the pump to carb line.

So... let the return line drain back to the tank if the float opens the needle valve. No problemo with that, is there? Why allow a pressure buildup in the line after shut down anyway?

There's no problem letting the return line draining back but you don't want the pump and the pump to carb line draining every time it shuts down. There is no pressure build up in a stock set up. Stock, pump pressure remains in the carb line and slowly drops to zero in several minutes. G.M.

[ford38v8]

You said a 2 1/2 lb check valve could eliminate the needle valve. No way.

[G.M.]

Originally Posted by ford38v8

You said a 2 1/2 lb check valve could eliminate the needle valve. No way.

YES WAY. Figure it out. G.M.

[expavr]

"The pump boiling is more difficult to over come. It looks like I may have finally have a sure solution but it requires installing a return line which a lot of people won't want to do. I never had any problems either until this stuff came along."

GM - I think you are on the right track with your fuel return VL2 theory.

I ran into a similar vapor lock condition with a hi-performance engine. The original fuel delivery system was set up to deliver 6-13 psi thru a boost referenced fuel regulator near the carb. Under load with all the engine heat the engine would periodically starve for fuel and quit. After much head scratching, some research, and tinkering I discovered that "deadheading" the fuel delivery at the carb created a situation where the heat buildup in the fuel delivery process caused the fuel to vaporize somewhere between the fuel pump, the fuel regulator and the carb. I added a fuel return line from the fuel pressure regulator to the tank and haven't had any vapor lock issues since then. I think that providing a fuel return system that allows the fuel to bypass a "deadhead" condition where a heat sink such as a fuel pressure regulator or an engine mounted fuel pump could cause vaporization will deal with the VL2 gremlin.

[ford38v8]

Originally Posted by G.M.

YES WAY. Figure it out. G.M.

No, you figure it out. Explain how a pressure check valve will maintain the correct fuel level in the float bowl, please? Do away with the needle valve and float? The float operates the needle, both are required.