Vapor Lock

Deuce Man

Deuce Man

Well-known member
I am sure this topic has been discussed to death on this forum, but here it is again. last night I drove the 46 down to our tuesday night cruise. All was well until I started it up to leave. It fired right up and soon stopped. I pumped the pedal, tried the choke, cranked some more and nothing. I suspected vapor lock as the temperature was in the eighties. I poured a bottle of icy water over the fuel pump and carburator, let it sit for 30 seconds or so, and it went right off. I drove it home without a hitch. My question is, exactly where is the pressure buildup?, is there an easy foolproof fix? Thanks, Rich
 
Overheating the mechanical fuel pump causes the fuel to vaporize. The mechanical fuel pump won't pump the vaporized fuel so no fuel moves until it is cooled back into a liquid.

I don't know how "easy" you might consider this "foolproof fix" to be but the fix is to install a backup electric fuel pump back by the gas tank to turn on when vapor locked to get the engine going again. I've used one and done that for years.

The quicker fix if you only have the problem after sitting like you had is to always have a jug of water in the car to pour on the fuel pump to cool it down immediately to get going again.
 
Henry, I did this on my merc powered 32. The mechanical pump seemed to have trouble drawing thru the elec pump. so I just eliminated the mechanical pump. The pressure regulator was another story. Those round chrome dial looking things are JUNK! I put a holley low pressure regulator in line and my car was totally dependable after that. What kind of elec. pump are you using? how is it plumbed? 6 or 12 volt? Thanks Rich
 
Deuce Man said:
Henry, I did this on my merc powered 32. The mechanical pump seemed to have trouble drawing thru the elec pump. so I just eliminated the mechanical pump. The pressure regulator was another story. Those round chrome dial looking things are JUNK! I put a holley low pressure regulator in line and my car was totally dependable after that. What kind of elec. pump are you using? how is it plumbed? 6 or 12 volt? Thanks Rich
Click to expand...

I use the Airtex E8902 for 6 volt inline with the mechanical pump. The mechanical pump has never struggled to pull though it. It is installed back by the gas tank in the frame rail.

Fuelpumpelectric.jpg


Because I often have to run the electric pump continuously I added a pressure regulator a foot from the pump.

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The last Vapour lock situation I observed on someone's vehicle it turned out to be the after market pump half the size of the Ford pump ,with the primer lever feeding two jugs ,these aftermarket gismos ,pressure regulators etc ,can cause problems . ,I suggest you go back to the original pump that set up for a Flathead motor that Ford spent millions developing .,with the built in right pressure and diaphragm ,Some one on here does the pumps maybe JM sedan , Ted
 
FlatheadTed said:
The last Vapour lock situation I observed on someone's vehicle it turned out to be the after market pump half the size of the Ford pump ,with the primer lever feeding two jugs ,these aftermarket gismos ,pressure regulators etc ,can cause problems . ,I suggest you go back to the original pump that set up for a Flathead motor that Ford spent millions developing .,with the built in right pressure and diaphragm ,Some one on here does the pumps maybe JM sedan , Ted
Click to expand...
Charlie ny does fuel pumps.
 
I'm also having a vapor lock issue.
(Old Henry helped on a different thread…thanks)
I ordered a K&N inline fuel pump rated at 1-2 PSI max.
That should be plenty for my application without killing the diaphragm in the mech. pump.
I plan on putting it on a switch so I can control the use.
 
FlatheadTed said:
The last Vapour lock situation I observed on someone's vehicle it turned out to be the after market pump half the size of the Ford pump ,with the primer lever feeding two jugs ,these aftermarket gismos ,pressure regulators etc ,can cause problems . ,I suggest you go back to the original pump that set up for a Flathead motor that Ford spent millions developing .,with the built in right pressure and diaphragm ,Some one on here does the pumps maybe JM sedan , Ted
Click to expand...

Ted it's not the pump, it's the corn gas. Real gas very seldom does this. G.M.
 
I agree with G.M. I had problems with vapor lock after driving for an hour and turning the car off for a few minutes. When I restarted it, it would quit after about 1 minute. I now fill up at a station with non-ethanol gas, and no longer have any problems.
 
flatheads had vapour lock problems long before ethenol was added to our gas. Have an electric pump on my 8ba, never had a vapour lock and have run "corn gas" since I got it on the road 16 years and 80000 miles ago. Fuel system (mainly the fuel pump) on flatheads was always a weak link. Solve all your problems with an electric pump and a pressure regulator.
 
rick r said:
flatheads had vapour lock problems long before ethenol was added to our gas.
Click to expand...

True statement, flatheads have always had vapor lock issues, BUT, the ethanol makes it worse is some cases. But, as Rick stated, an electric pump will solve it.
 
JSeery said:
True statement, flatheads have always had vapor lock issues, BUT, the ethanol makes it worse is some cases. But, as Rick stated, an electric pump will solve it.
Click to expand...

So will a small fuel return line after the fuel pump. I don't like
electric pumps. G.M.
 
This works for me ,running these pumps for 20 years now .Cold start the other day. barely one turn to running with a small VW battery .See the hand primer cannot remember the last time I used it ,if it sat for four weeks then maybe . after the pump is set up it must be pressure checked .Ted
 

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I put one in about 1998 nothing special about it ,I have had no problems with it .Macs is one source ,and I can supply new kits if needed .The pump hat must be air tight , There is a re popped pump out there with a hand primer of about 2" across I would steer clear of them .Ted
 
Most other car makes used the A/C pump like Ford ,millions made ,! so what's the difference ?? ,Chev have the pump low so there is a positive fuel supply in the line and the tank out let low ,Ford had a flex line from the pump on the in put side ,that more than often had air leaks, likely on re popped ones .This allowed flow back . Ford has a push rod .?? etc. Ted
rick r said:
flatheads had vapour lock problems long before ethenol was added to our gas. Have an electric pump on my 8ba, never had a vapour lock and have run "corn gas" since I got it on the road 16 years and 80000 miles ago. Fuel system (mainly the fuel pump) on flatheads was always a weak link. Solve all your problems with an electric pump and a pressure regulator.
Click to expand...
 
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