Vapor Lock

49Hudson

I have a 49 Hudson with a Super 8 engine that vapor locks when the engine gets hot.  There is a filter bowl inline just as the fuel line enters the cab.  You can see the fuel boiling in the filter bowl when it is hot, and the filter housing gets so hot you can't hold your hand on it.  The heat shield appears to be too small.  Is this a common issue with these engines, and what is the solution?

I currently have the fuel line and filter wrapped in aluminum foil, and that seems to be working on fifty mile runs or less in 70 F temperatures.  Any advice?  I have heard that a wooden clothes pin clamped on the fuel line works, but I can't see how.  The last time it vapor locked, it was pushing fuel out of the fuel filler tube (gas tank).  I was parked on an incline ( side to side) with the filler neck on the low side.

Jim Tarleton

Geoff

Check that your fuel pump  has all the insulating sleeves and washers on the mounting bolts.   There should be a fiber washer under the bolt heads and an insulating sleeve around the bolts.   Also check that the  feed pipe from the pump is routed well away from the exhaust manifold. And there is an insulating and spacing stack between the pump and block.     Extend that  heat deflector too  - not a difficult job to make up a bigger one. I don't know that aluminium foil will do much -- it conduct heats pretty good, rather than reflects it away.
Geoff 

Hudson Grandpa

The first thing I did was to get rid of the fish bowl.  You got fuel sitting outside of the carb in glass that's percolating.  As Geoff says nix on the aluminum foil.. I took regular black fuel line, (rubber) slit it lengthwise and wrapped in around the fuel line, especially coming out of the fuel pump to the carb.  I live in TX, 100 degrees, and no percolating even waiting at the stop light.  Of course if you shut it off, you'll have to wait awhile to get it started again.

hudsn47

Jim, In addition I would also look at your manifold heat riser on the eight cylinder. Its probably stuck closed and that will heat things up under the carburetor and cause engine overheating. I've heard of this causing head gasket failure and on the extreme end even a cracked headl. Anyway I elimimated mine recently and the percolating went away and it runs cooler. If you decide to do it you can eliminate the heat riser without removing the exhaust manifold from the car. Doug

Jon B

Did you say that the glass bowl is next to where the fuel line enters the carburetor?  If so, maybe the carb is getting hot, and transferring that heat to the glass bowl.  Do you have plenty of fiber spacers between the manifold and the carb?  On my car (a 1937 6-cyl) I have 4 spacers, then the metal heat deflector, then 4 more spacers.  I never have vapor lock. Another thought.  Originally I think they wrapped the exhaust pipe in asbestos where it passed under the carb and fuel pump.  You might try doing that with whatever substitutes for asbestos nowadays.  And while you're at it, wrap it around the fuel lines as well!

Uncle Josh

Fuel boiling in the line smacks of too much vacuum as any liquid will boil at low temps under vacuum.  I'd check for a restriction in the tank or fuel line..and make sure the screen in the fuel pump is not plugged.  BTW. the clothes pins are an old wives tale.

Per

Jim,

     One owner of a '35 Hudson 8 solved his vapor lock problem in an unusual way.  He draped a mop over the fuel pump, and attached a small basin just below the pump, with the ends of the mop going into the basin.  When he uses the car in hot weather, he pours water on the mop and fills up the pan.  His fuel pump is easier to reach than yours, however.

                  Per

RonS

Many things can cause vapor lock or it's forerunner, fuel starvation. I assume that the fuel pump has good PSI and suction? And, the valves are properly adjusted. I solved mine by 1. Adding a phenolic spacer sandwiched between two paper gaskets under each carb in the twin H WA-1s.  '95 Ford f150s spacers will fit. 2. There is a heat shield above that bunch. Now add 3-4 paper gaskets above the heat shield. The two bolts holding the carb to the manifold must be long enough to accommodate this "stack".3. Next move the fuel line away as far as possible from the exhaust manifold.4. Wrap the carb line with a Mylar tube( Jeggs sells 'em).5. Use a  fuel flex line  to the inlet on the fuel pump. 6. Place a Mylar pad over the fuel pump between the pump and the exhaust manifold to reflect the heat away from the fuel pump.  Again,see Jeggs.  I really like the Craig valves in the float bowl. An solenoid style electric fuel pump in line can't hurt. Do not forget Stabile if the car is used infrequently. 7. As Geoff said, there are 2  bolts holding the fuel pump to the block. These 2 bolts originally ran through a "straw tube " of phenolic material that acted as an insulator, and prevented heat transfer to the FP body. Good luck and be patient.

49Hudson

I just discovered the car once had an electric fuel pump activated by my mystery switch under the dash.  I may re-activate it if it is still there.

Jim