Carburetor Percolation Fix

[meadowbrook]

Hi all.

 

I have posted in the past concerning an issue I run into on hot days in my '50 Meadowbrook where I will be either idling for a long time or slowing down after a highway blast and the engine will eventually stall and not start for some 10 minutes.

 

Responses from the group seemed to indicate a carb percolation issue where the fuel in the bowl actually boils away.

 

So do I have to create a carb heat shield and/or a non metallic spacer between the carb and intake or are there any available components in the marketplace I could buy?

 

I am leaning towards a spacer as opposed to a shield because a shield would have to clear linkages and such, and would seem more complicated.

 

Just for your info, the engine is in great tune, carb is recently rebuilt and cooling system is in good shape as the car never overheats.

 

Thanks!

[Don Coatney]

What is your carburetor float level?

[TodFitch]

When my car has the symptoms you describe, I can get it going again by pouring some water on the fuel pump. Seems like the fuel in the pump gets too hot and some of it vaporizes. Since the fuel pump is no where as good at pumping vapor as it is at pumping liquid the carburetor runs out of gas. I call it vapor lock though that may not be the correct term. Cooling the fuel pump eliminates the vapor in the pump and it starts working again. Presumably appropriate routing of fuel lines and having the fuel pump heat shield installed should reduce this particular issue. However I did a test on a recent hot day and was still able to reproduce the problem on my car. . . Maybe the pump is a bit weak on my car to begin with and that is making the high temperature situation worse (putting a fuel pressure check on my list for the next time I am going over the car).

 

If your car was running fine when parked and you go back to start it again after a few minutes and it does not start, then I'd expect that to be due to percolation (vaporization) of fuel in the carburetor bowl leading to raw gas getting into the manifold. Call it flooding due to percolation. This is not what you describe in your posting. So adding a spacer or heat shield to your carburetor probably won't fix your problem.

 

You can double check which of the two issues you have by pulling off the air cleaner and checking for symptoms of flooding next time it does this. If it is percolation then I'd expect you to see gas in the manifold. If the pump failed to pump because of heat your carb bowl would be dry (or at least very low) and your accelerator pump probably won't be putting gas into the venturi when you actuate it.

[Lumpy]

Making a heat insulater from thin aluminum plate is easy, easy to cut holes and slots for linkage or whatever. Spacing the carb up on a non-metalic spacer could help, but I wouldn't go over 1/2". And a heat shield for the pump can't hurt. Is your engine running especially hot for any reason? Thermostat? Lumpy has a 190, which I should switch out, but I've never had a vapor lock or perculation/vaporization problem.

 

Anyhow, I'd do all the heat shield stuff and then see what happens. Might not fix the problem, but it would be a start, and anything you can do to cool things off would be good. ??

 

ken.

Edited May 9, 2014 by Lumpy

[navyboy]

I also insulated all my fuel lines to keep heat away, I used reflective blanket heat shielding ovver all the lines that enter the engine bay to the pump and then pushed stainless braid hose over my hard line from the pump to the carb and helped a lot. I also have the heat shield for the fuel pump and took some metal reflective tape that sticks very well and shapes easily over the fuel pump and shield and stuffed some insulator between the pump and the shield. The biggest thing that helped me hands down though was installing a 6v electric fuel pump back by the tank wired up to a switch  under the dash, that solved every issue I had and has been great since the pump install, I run it with my mechanical pump still inline but you can bypass the mechanical pump is you want and keep it on the block, I would just plug the in/out of the mechanical pump if you wanted that route but I would just leave it inline and use both.

[JDaniel64]

A weak/old fuel pump will definitely exacerbate the problem. A few years ago my engine would cut out/stumble and stall real bad at operating temps, rebuilt the carb and it helped but on the hot days (90+) the problem would show back up. New pump helped bunches, still can see a tiny bit of weeping from the carb on the hot days but causes no ills, outta address it though for safety's sake. When the car was bought it had a 1/2" phenolic spacer which probably aids in decreasing heat transfer.

Edited May 9, 2014 by JDaniel64

[dlrides]

I'm addressing this very issue tomorrow, and plan on covering all the bases.

 

) Fabricating a carb heat shield and covering bottom with heat blanket left over from another project.

 

) Bought a 3'length of 2,000 deg tubing insulation from Jeg's for fuel line.

 

) You're gonna like this: fabricated a cover for the fuel pump out of a baked beans can, and covered with the same heat blanket. Easy to do with a 3.5" can, just cut a couple of slots for the vacuum lines and slip over the pump.

[hendo0601]

Beans beans the magical fruit the more you eat the more you can....insulate fuel pumps with the left over cans? That is a terrible song...

[Lumpy]

Sometimes heat can build up in the engine compartment, hot air from the radiator kind of stalls out and can't get out as fast as the fan and wind pushes it in. I think that's why some old cars had louvers in/on the inner fenders. I know when people louver thier hoods on rods, it reduces heat for that reason, it's actually functional. However, probably not many of us would want to louver our hoods.

 

I like the bean can thing. Used to do that to make heat shields for starter motors, or on headers where they passed close to stuff that you didn't want to bake...like...starters.

 

ken.

[William Davey]

I don't know if aluminum is a good choice for a carb spacer.  Aluminum conducts heat very well, that's why it heats and cools so quickly.  Seems like any intake manifold heat would quickly make it's way to the carb.  Melamine might be a better choice.

[1941Rick]

My question would be.....is the plate for the heat riser still intact?

[Lumpy]

Right, for a spacer, aluminum is not the best choice. Believe it or don't, hardwood makes good spacer material, very easy to work with. A good cut of a good hardwood won't split or crack, especially if you don't over torque the carb down, which one should not anyways. Rosewood and Ironwood would both be very indestructible, but any good hardwood will do.

 

Aluminum is a good choice for a "plate", or "shield" that goes under the carb, usually between the manifold and spacer, or carb, and reduces, or keeps, or disrupts some of the heat that rises off the manifolds. They work. Used to make those for small and big blocks, V8's, all the time. Easy to make. You can get very creative with them too, in order to avoid interference with linkage or other things.

 

k.

[hendo0601]

On my 63 dodge polara I was having problems with gas boiling in the carb on a hot day after shutting her down. I couldn't install a big spacer under the carb as the high rise single plane intake already had the carb mighty close to the hood. So I took a piece of 1/4" aluminum plate and cut it into a rectangle that was basically the same dimensions as the entire carb, drilled some holes and trimmed it to fit around the linkages and stuck it between the carb and the intake. It worked perfectly to absorb heat and dissipate it before transferring it to the carb, thus eliminating the problem of fuel boiling away after a hot shutoff. I got fancy and polished it so it looked shiny and less homemade.

[Don Coatney]

It will be interesting to see what the real problem is.

[meadowbrook]

What is your carburetor float level?

It was at the specified level on the rebuild kit when I rebuilt it. I have lowered it slightly since then in an attempt to solve this.

I have not had issues with hot restarts. One thing that does seem to help is to keep the engine revving higher when in traffic, so I suppose the extra air flow helps to cool the carb.

Next time it happens I will pull the air cleaner and peek inside as I activate the throttle to see if I get any fuel to flow from the pump jets.

Thanks so much for the outpouring of responses.

The carb is the wrong one for the engine as I found out, it is a Carter BB.

[TodFitch]

. . . I have not had issues with hot restarts. One thing that does seem to help is to keep the engine revving higher when in traffic, so I suppose the extra air flow helps to cool the carb. . . 

I still think you should look at your fuel pump.

[Don Coatney]

Hi all.

 

I have posted in the past concerning an issue I run into on hot days in my '50 Meadowbrook where I will be either idling for a long time or slowing down after a highway blast and the engine will eventually stall and not start for some 10 minutes.

 

Responses from the group seemed to indicate a carb percolation issue where the fuel in the bowl actually boils away.

 

So do I have to create a carb heat shield and/or a non metallic spacer between the carb and intake or are there any available components in the marketplace I could buy?

 

I am leaning towards a spacer as opposed to a shield because a shield would have to clear linkages and such, and would seem more complicated.

 

Just for your info, the engine is in great tune, carb is recently rebuilt and cooling system is in good shape as the car never overheats.

 

Thanks!

 

 

It was at the specified level on the rebuild kit when I rebuilt it. I have lowered it slightly since then in an attempt to solve this.

I have not had issues with hot restarts. One thing that does seem to help is to keep the engine revving higher when in traffic, so I suppose the extra air flow helps to cool the carb.

Next time it happens I will pull the air cleaner and peek inside as I activate the throttle to see if I get any fuel to flow from the pump jets.

Thanks so much for the outpouring of responses.

The carb is the wrong one for the engine as I found out, it is a Carter BB.

Guess I was confused and thought you had problems with hot starts.

[meadowbrook]

When it stalls, I can't restart for ten minutes. But I never had an issue with shutting the car off and then restarting shortly after.

[55 Fargo]

Fuel pump ????????