Vapor lock 47 Merc.

Displayman

Displayman

Senior Member
Anybody have any good tips for avoiding vaporlock.
My wife was driving our 47 Merc. convert. from the
interior shop. 92 degrees outside, cruising down the road about
55 mph. and all of of sudden she is waving me to the side.
I was following with our Dodge ram 2500 until we have confidence ion the car.
This is only the third time we had it on the road since we bought it.
This car has a brand new mechanical fuel pump, new plugs,new gas tank,
new sender. I just(now) covered the fuel line from the pump with a rubber
hose to protect it from the engine heat. Doesn't look stock, but I would
rather get to where I am going, than looking correct on the side of the road. Incidently, we broke down on a country road in front of a hog farm
with us bening down wind. PHEW!!!!!!!!
Appreciate any suggestions, maybe electric fuel pump?
Thanks,
Bob- Hampshire, Illinois
 
Sounds like classic "vapor lock" caused by an over heated coil. Send your coil to Skip to modernize and you will never experience "vapor lock" again. Then you can "trust your Merc" without an escort.
John
 
Make sure all your fittings are tight, glass bowl is tight, then use Marvel Mystery Oil in each tank as per instructions on container. the MMO really
helps with the vapor lock. if all else fails install a electric pump as a backup. ( sometimes this makes things worse, mechanical pump doesn't
like to pump thru the elec. pump) been there done that. removed the elec. and no more vapor lock for me. others will disagree I am sure.
but the MMO does help.
Jim

Yes, you also need a good coil that won't quit when it gets hot then works when cools off.
 
The only Flathead of ours that I've ever experienced "vapor Lock" in is our '39 LZ V-12 and it's got nothing to do with the coil... I think the problem is in the locking gas cap (Ford Accessory) that is on the car. The vapor loc has only occurred three times, each time was after the car sat for a least an hour after a normal run (no overheating). What happened is this; the car would fire up and run just long enough to deplete the fuel in the float bowl. No fuel would pump from the stock fuel pump to the carb. The solution each time was to remove the locking gas cap and try to start again. After a few cranks fuel started to flow and she fired up... that said, I would still check the coil especially if you are using a stock Ford unit.
 
As has been mentioned, ignition problems can be exacerbated by heat but not nearly as often as the fuel vaporing in the line. A fuel pump just can not pump a vapor. Put an electric pump as close to the tank as possible and you will be able to get fuel to the engine when it is hot. This will force liquid fuel through your mechanical pump and to your carb(s) and you can stay running.
Anyone who says that there isn't anything as "Vapor Lock" just has never really driven in the heat with these old vehicles before. Come down South and try some real heat!
When I was driving my 1939 Ford back in the 60's I would always take the side panels off when the temps got warm and if I ever stopped for a "Coke" at a "Drive In" I would have to wait till I finished it so I could place the cup of ice on the fuel pump to cool it so the engine would start. Funny, I never had to put ice on my coil???? I never lost ignition, just the ability of pumping fuel to the carb!
 
No doubt, there is vapor lock, but as stated many times it is traced to a coil problem. I have driven my 39 for over 50,000 miles now with no electric pump and no Marvel Mystery Oil. It has been driven in 90+ weather and in 4th of July parades and I have never experienced vapor lock.
 
While tracing the history of my car I was told the owners girl friend drove the car to work every day. The distance from her home to her workplace was 10 miles. She carried a gallon of water on hot days. Around the half way point the car would vapor lock. She would throw the water on the intake and it would fire up. That intake is the one pictured in my avitar.
 
I had it happen even after a rebuilt coil. I drove into a car show in 85F weather. About an hour or so later I went to leave, car fired up and quit. Wouldn't start. Drained the battery, jumped it, checked spark. Finally went and got some starting fluid. A couple shots, car fired up and we watched a few bubbles run through the float bowl. I finally figured out I had an exhaust gasket leaking and blowing hot exhaust directly on the fuel line (copper). I would suggest you check around the exhaust manifold.
 
I have owned my 39 for over 45 years and have never had it vapor lock while going down the road, only after stopping and the fuel pump heat soaks and gets the fuel hot enough to vapor off. I never put an electric pump on it until a few years ago just to prime it prior to starting it after an extended period of sitting. Conserves battery. Never have put MMO in tank but with the new corn gas it might be a good alternative since the corn fuel has a higher vapor pressure than the real stuff! Still running an original Henry coil and have never had any ignition related problems other than a tune up every 20k miles.
 
The 39 Ford with 60 HP was fun sorting out all the issues.

First found the coil overheated, made a plate and hung a 46 coil out of the heat. Do not forget modern condensers do much better. Find out if someone local to you that has a coil condenser tester as that will make your trouble shooting easier. If you have an extra coil you could just put a modern coil off to the side using the plate off the bad coil to get the spark to where it needs to go.

Then we had an actual vapor lock, no fuel in the carb. Keep in mind this long predates modern fuel by 20+ years. Rebuilt the fuel pump with a recent new kit.

After that it did much better. Still was not a happy camper on the 4 of July parades and it loved running flat out on the highway. The only complaint was the brakes. They would still muck up every couple of years. Sold the car ages ago.
 
The Merc. was converted from 6 volt to 12 volt.
New 12V coil, new condenser, rebuilt 6V starter, new 12v solenoid, new gas tank, new sender,new plugs,fresh gas, the only thing I just did was encase the fuel line
in rubber hose to insulate from heat. Drove it yestersday no vaporlock,
but it was only 85 not 92 degrees as it was when it vapor locked before.
 
My '50 Ford vapor locks every time I drive it in hot weather. It runs fine on the road, but just last evening, I drove it about 12 miles and parked it for less than 2 hrs., started it up and drove it about 200 ft and it quit. I switched on the electric pump for a few seconds, started it up and drove it home. I usually just turn on the electric pump after each stop until I get rolling and it will run all day and not miss a beat. Been that way for 6 or 7 years. I have driven it from WV to Ga., Ct. NY, In, and Dearborn, Mi., and as long as I turn on the pump at each stop, It never misses a beat. Planning to drive it to Charlotte and St George, Ut yet this year.
 
My 51 would do that same thing in hot weather, I removed the electric pump and no more problems. I carry it in the trunk for a spare also a spare mechanical pump, never used them. first try 8oz of marvel mystery oil at fill up in hot weather, that seemed to really help.
Jim
 
Back in the fifties I had a '40 Ford with a flathead. I remember my father telling me to put a hollowed out half lemon peel on the fuel pump to insulate it from the heat. Can't remember if it worked or not.
 
Ross
I assuming your carb was out of fuel or not enough to start it ?? Carb leak down

Ross in East Texas said:
As has been mentioned, ignition problems can be exacerbated by heat but not nearly as often as the fuel vaporing in the line. A fuel pump just can not pump a vapor. Put an electric pump as close to the tank as possible and you will be able to get fuel to the engine when it is hot. This will force liquid fuel through your mechanical pump and to your carb(s) and you can stay running.
Anyone who says that there isn't anything as "Vapor Lock" just has never really driven in the heat with these old vehicles before. Come down South and try some real heat!
When I was driving my 1939 Ford back in the 60's I would always take the side panels off when the temps got warm and if I ever stopped for a "Coke" at a "Drive In" I would have to wait till I finished it so I could place the cup of ice on the fuel pump to cool it so the engine would start. Funny, I never had to put ice on my coil???? I never lost ignition, just the ability of pumping fuel to the carb!
Click to expand...
 
jdl said:
My 51 would do that same thing in hot weather, I removed the electric pump and no more problems. I carry it in the trunk for a spare also a spare mechanical pump, never used them. first try 8oz of marvel mystery oil at fill up in hot weather, that seemed to really help.
Jim
Click to expand...

I always use MMO.
 
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