Electric fuel pump for SUs in hot weather

[spock345]

In my endless pursuit of preparing old cars to drive comfortably in triple digits I've become curious about electric fuel pumps to help with fuel vaporization issues on an SU equipped B20 on hot days. Mostly when the car sits and it takes a bit to get it going happily again due to fumes built up in the lines and bowls. Has anyone had success addressing this with an electric pump? If so what electric pump is recommended?

 

[JohnMc]

I'm not doing it for vapor lock, or using it with SU's, but I did stick a Holley carb electric pump back by the tank on my PV. It puts out 7 or 8 psi, lots of flow, and I use a fuel pressure regulator to knock that down to about 2.5 psi for the DCOE's.

The DCOE's did NOT like the mechanical pump I had on it, too much pressure, although I could probably have used a regulator on it as well. But really, it just works better. When the car sits around for a while, the fuel evaporates out of the carbs, and with the mechanical pump you're doing a bunch of cranking until it finally gets fuel into the bowls again. With the electric pump, it fills the bowls when you turn the key on, and it starts right away when you crank it.

Also, if you ever run out of gas, it's WAY nicer to just turn the electric pump on and have it clear all the air from the lines, instead of cranking for a minute or two.

 

[James M]

I get a hardon for mechanical fuel pumps, all my carbed cars have and will continue to have them for my ownership. I never had any hot start issues with my B18 SUd Amazon the last two summers in Davis, lots of 100°+ days.

I do work on a good number of cars with electric pumps running carbs though, they are better for cars that sit I guess. The only time I've had issue was with some MGB SUs that kept flooding on highway cruising speeds and needed an external regulator. Otherwise a low pressure pump like the Edelbrock 30 GPH Fuel Pump 17303 would be my go-to.

 

[spock345]

I get a hardon for mechanical fuel pumps, all my carbed cars have and will continue to have them for my ownership. I never had any hot start issues with my B18 SUd Amazon the last two summers in Davis, lots of 100°+ days.

I do work on a good number of cars with electric pumps running carbs though, they are better for cars that sit I guess. The only time I've had issue was with some MGB SUs that kept flooding on highway cruising speeds and needed an external regulator. Otherwise a low pressure pump like the Edelbrock 30 GPH Fuel Pump 17303 would be my go-to.

Currently I actually have a regulator. It seems that there are two issues with the aftermarket mechanical pumps, they push too much pressure, and the mating surface for the gasket isn't quite flat. If I don't go electric I may try to find an older rebuild-able pump that seals to the block right.

If anything I am probably just gonna reserve a spot on my relay/fuse bar in the engine bay for a pump relay and fuse just in case.

 

[James M]

Currently I actually have a regulator. It seems that there are two issues with the aftermarket pumps, they push too much pressure, and the mating surface for the gasket isn't quite flat.

If you already have the regulator I'm sure you could slap on an electric pump and see if it helps. I've yet to have an Edelbrock one fail and being a parts store thing it's easy to warranty locally anywhere. Mounting is better than some of the cheaper ones you basically ziptie to a frame rail. I bet 2 Kjet dizzy mounts would be perfect.

That mating surface issue I've been told occures if they get overtightened since they are soft aluminum. I've got one pump with a full millimeter bow in it.

 

[spock345]

If you already have the regulator I'm sure you could slap on an electric pump and see if it helps. I've yet to have an Edelbrock one fail and being a parts store thing it's easy to warranty locally anywhere. Mounting is better than some of the cheaper ones you basically ziptie to a frame rail. I bet 2 Kjet dizzy mounts would be perfect.

That mating surface issue I've been told occures if they get overtightened since they are soft aluminum. I've got one pump with a full millimeter bow in it.

I'd like to find a glass bowl or competition service/penta pump for it. Threaded fittings would be cool.

I wouldn't be surprised if it were overtightened, there were some strange shade tree mechanic "fixes" to the fuel system when I got the car.

 

[James M]

I'd like to find a glass bowl or competition service/penta pump for it. Threaded fittings would be cool.

I wouldn't be surprised if it were overtightened, there were some strange shade tree mechanic "fixes" to the fuel system when I got the car.

Glassbowl > Everything, such a good look and the hand priming lever. There are a few rebuildable cores on ebay for ~$50, Just gotta make sure it's the style with rebuild kits available.

 

[bobxyz]

My old Land Rover, with a Weber 32/36 DGV carb and a thin right-angle intake adapter, had horrendous vapor lock problems when going up the mountains, or after sitting for just a few minutes when hot. I added a Facet electric pump (looks like a brass box with inlet/outlet nipples) as close to bottom-of-the-tank level as I could, with a switch in the cabin. The fuel line then went into the mechanical pump (yes, with a glass bowl and hand-prime lever). If it was having vapor lock problems, I'd just flip on the pump until it cooled down. It was also nice to prime if it had been sitting for a few weeks.

IIRC, there were different pressure Facet pumps available. It was noisy (tap-tap-tap-tap-tap-tap....), so get the rubber mount or use a few layers of rubber inner tube to quiet it down.

 

[spock345]

My old Land Rover, with a Weber 32/36 DGV carb and a thin right-angle intake adapter, had horrendous vapor lock problems when going up the mountains, or after sitting for just a few minutes when hot. I added a Facet electric pump (looks like a brass box with inlet/outlet nipples) as close to bottom-of-the-tank level as I could, with a switch in the cabin. The fuel line then went into the mechanical pump (yes, with a glass bowl and hand-prime lever). If it was having vapor lock problems, I'd just flip on the pump until it cooled down. It was also nice to prime if it had been sitting for a few weeks.

IIRC, there were different pressure Facet pumps available. It was noisy (tap-tap-tap-tap-tap-tap....), so get the rubber mount or use a few layers of rubber inner tube to quiet it down.

I had that issue with a DGV as well. I somewhat fixed it with an intake spacer to try isolating it from the manifold.

An auxiliary electric pump on a switch is a decent idea.

 

[James M]

No issue with the mechanical pump attempting to pull through the electric one?

 

[bobxyz]

It worked fine for me. I had the same setup on a vw dune buggy, not for vapor lock or running, but just for priming after sitting through the winter months, and it was good too. Both used Facet pumps, so there may be something unique about them compared to rotary pumps.

 

[spock345]

It worked fine for me. I had the same setup on a vw dune buggy, not for vapor lock or running, but just for priming after sitting through the winter months, and it was good too. Both used Facet pumps, so there may be something unique about them compared to rotary pumps.

Nice, I was looking at the little square facet pumps. I think at this point I'll just make sure I've got a spot for a relay and fuse for if I ever want to add a pump and run the mechanical for now.

 

[142 guy]

Going back to your very first post which focused on fuel vaporization. In order to eliminate vapor formation on hot days you have to maintain the fuel under pressure. Around 30 psi would probably be the minimum. Short of the elaborate vapor control schemes applied to carbs in their final days in OEM applications there is nothing you can do to fix that problem because by design the float bowl must be vented to atmospheric pressure.

If you want to eliminate vapor formation in the fuel line up to the carburettors, you could install a high pressure electric fuel pump (fuel injection style) back at the tank where it is relatively cool. Supply high pressure fuel to a regulator(s) just before the carbs which drops the pressure low enough to prevent flooding of the float bowls. The regulator located in front of the carbs will require a separate fuel return line because of the way they manage fuel pressure. You may require two regulators in series because the regulators that can manage the flows associated with EFI style pumps do not work well at low control pressures. Both the high pressure and the recirculation through the return line should eliminate any vapor lock effects. This is a lot of work to do correctly so you want to make sure that the problem is real.

Most of the electric fuel pumps designed for carb operation are diaphragm pumps, just like the mechanical fuel pump attached to the engine block. That is why they have that characteristic tick, tick tick. They are by design pressure limited. They may operate at a slightly higher pressure than the original mechanical fuel pump; but, will not generate enough pressure to prevent vapor formation in the fuel system. However, a significant contributor to vapor formation may be the mechanical pumps attachment to the side of the engine which provides a nice opportunity for heat soak on shut down. Replacing the mechanical fuel pump with an electric pump back by the tank should eliminate the mechanical fuel pump's contribution to vapor formation which may eliminate most of your vapor formation problems in the fuel line. Replacing steel fuel line in the engine compartment with rubber fuel line may also help because of the thermal insulation provided by the rubber. Adding an electric pump back by the tank while keeping the mechanical fuel pump would help address problems with priming the fuel system; but, will do little to nothing in terms of reducing vapor lock problems.

 

[spock345]

Glassbowl > Everything, such a good look and the hand priming lever. There are a few rebuildable cores on ebay for ~$50, Just gotta make sure it's the style with rebuild kits available.

Are there glass bowl pump variants that don't have rebuild kits available? I am not particularly well versed in those parts. I know where I can find a penta/competition service pump though. Has a priming lever and takes the same diaphragm as some of the pierburg pumps.

Going back to your very first post which focused on fuel vaporization. In order to eliminate vapor formation on hot days you have to maintain the fuel under pressure. Around 30 psi would probably be the minimum. Short of the elaborate vapor control schemes applied to carbs in their final days in OEM applications there is nothing you can do to fix that problem because by design the float bowl must be vented to atmospheric pressure.

If you want to eliminate vapor formation in the fuel line up to the carburettors, you could install a high pressure electric fuel pump (fuel injection style) back at the tank where it is relatively cool. Supply high pressure fuel to a regulator(s) just before the carbs which drops the pressure low enough to prevent flooding of the float bowls. The regulator located in front of the carbs will require a separate fuel return line because of the way they manage fuel pressure. You may require two regulators in series because the regulators that can manage the flows associated with EFI style pumps do not work well at low control pressures. Both the high pressure and the recirculation through the return line should eliminate any vapor lock effects. This is a lot of work to do correctly so you want to make sure that the problem is real.

Most of the electric fuel pumps designed for carb operation are diaphragm pumps, just like the mechanical fuel pump attached to the engine block. That is why they have that characteristic tick, tick tick. They are by design pressure limited. They may operate at a slightly higher pressure than the original mechanical fuel pump; but, will not generate enough pressure to prevent vapor formation in the fuel system. However, a significant contributor to vapor formation may be the mechanical pumps attachment to the side of the engine which provides a nice opportunity for heat soak on shut down. Replacing the mechanical fuel pump with an electric pump back by the tank should eliminate the mechanical fuel pump's contribution to vapor formation which may eliminate most of your vapor formation problems in the fuel line. Replacing steel fuel line in the engine compartment with rubber fuel line may also help because of the thermal insulation provided by the rubber. Adding an electric pump back by the tank while keeping the mechanical fuel pump would help address problems with priming the fuel system; but, will do little to nothing in terms of reducing vapor lock problems.

Interesting. Eliminating a source of heat is definitely a benefit. I was also under the impression that the electric pump, since it can provide pressure before starting the engine, helps purge the lines of the vapor produced somewhat.

Your point regarding requiring EFI pressures to prevent vapor formation is a good one. Plumbing a return line is probably more effort that I want to get into for what in the end is a minor annoyance. Mitigating vapor formation or its symptoms is probably a better way to describe my goal.

 

[142 guy]

Interesting. Eliminating a source of heat is definitely a benefit. I was also under the impression that the electric pump, since it can provide pressure before starting the engine, helps purge the lines of the vapor produced somewhat.

In order to purge the fuel line you have to generate flow. On a carb engine, if the engine isn't running the only way you can generate flow is to pressurize the fuel line so much that it pushes open the float needle and floods the float bowl. If you can generate enough pressure in the fuel line you can cause some of the vapour to transition from the vapour state back into the liquid state; but, you are no going to do that with an electric pump meant for carbs.

If you can eliminate or manage the heat, you will eliminate most of your vapour lock problems. Do you SUs still have the heat shields which are meant to reduce fuel boiling in the float bowls? Placing the carbs directly over the exhaust manifold is not particularly helpful.

 

[JohnMc]

If the carb bowls have fuel and the needle valves aren't open, then you don't need to purge vapor from the lines (at that point), the carbs don't need any more fuel than they've got.

Once they're lower on fuel, the float will drop and the needle valves will open, and any vapor in the line between the pump and carb will get vented, before liquid fuel fills the bowl and shuts the valve again.

And yeah, having the proper heat shields is important. The older HS style carbs need one style of shield that covers the offset bowls, the later HIF's need a different style that covers the integrated bowls.