Vapor Lock/Electric Fuel Pump

[Steven]

I had the great pleasure of experiencing my first vapor lock yesterday (a 93F plus day in Los Angeles and a prolonged idle).

I've been reading all of the existing threads, and seeing a lot about electric fuel pump swaps for mechanical, relocating to the trunk and other places.

I would love to figure out the best setup to implement and am seeing lots of opinions (ie cylinder electric fuel pumps vs a boxy Facet fuel pump), various kill switches, and relocation spots (trunk, relocating within the engine compartment, etc). Would love thoughts on people's success stories and what I should do for best results in preventing future vapor lock...would be a shame to feel like I can't drive my coupe in warmer weather in the future for fear of being stranded/delayed.

Thanks!

 

[dang]

Where is yours located?

 

[adawil2002]

If you are running a mechanical pump off the cam, put a supplemental electric pump. It can be switched on on those 93+ days when needed & switched off when not. We did that with our 1933 Packard Twelve, which had an updraft Stromberg Carb. Vapor lock was a real problem until we installed the switchable electric pump which solved the problem.

 

[dang]

Ah, I didn't get that it was still a mechanical pump. I just mounted my Facet electric pump over the weekend and put it under the left rear seat where the fuel line goes from the center over to the left rocker (E3). Seems like it would get enough air flow there to stay cool, along with the fuel keeping it cool, so I doubt the pump would contribute to the problem.

 

[Nachtycoupe]

Ah, I didn't get that it was still a mechanical pump. I just mounted my Facet electric pump over the weekend and put it under the left rear seat where the fuel line goes from the center over to the left rocker (E3). Seems like it would get enough air flow there to stay cool, along with the fuel keeping it cool, so I doubt the pump would contribute to the problem.

View attachment 91426

Hey Dan, after reading this and other vapor lock threads this seems like a good idea, however I have a question. Wouldn't this cause a full-time restriction? Mechanical pump would have to pull harder through it, no? Have you had any issues since installing? I have had vapor lock twice now, once when I replaced an aftermarket BMW black plastic cap that was on the coupe when I bought it with a factory period correct aluminum one. Then almost immediately (that next day) it locked up. So, I switched back and didn't have any issues.

Recently after driving in 80+ degree weather, sitting on a hot track, doing three laps on the track, then driving another 45-min home after car sat for a while after the track time, I stopped off at the golf course, had a soda, drove a few hundred yards and it sputtered and quit again. I removed the cap, sprayed some starter fluid in carbs, checked bottom of car to make sure it wasn't something more, oil leak, etc waited for about ten minutes, replaced the cap, started up and idled normal and made it home fine. I will inspect the entire fuel line to see if it is coming into contact with a heat source but now I am scratching my head as to the cause. Before I just figured it was the cap, since I just replaced it. And I read on here a vented cap is not necessary. I am running Webers 32/36 DGAV with recently replaced electric cold start vs. water. Idles just fine, cold start works great, so not sure that conversion would have anything to do with it as the vapor lock happened before I put in the electric cold start the 1st time. It does suck when this happens, and always no shoulder! to pull over in... Arrrrgh.

 

[Dan Wood]

I had the great pleasure of experiencing my first vapor lock yesterday (a 93F plus day in Los Angeles and a prolonged idle).

I've been reading all of the existing threads, and seeing a lot about electric fuel pump swaps for mechanical, relocating to the trunk and other places.

I would love to figure out the best setup to implement and am seeing lots of opinions (ie cylinder electric fuel pumps vs a boxy Facet fuel pump), various kill switches, and relocation spots (trunk, relocating within the engine compartment, etc). Would love thoughts on people's success stories and what I should do for best results in preventing future vapor lock...would be a shame to feel like I can't drive my coupe in warmer weather in the future for fear of being stranded/delayed.

Thanks!

This thread will explain how others have addressed vapor lock.

Thread 'Electric fuel pump to prime carbs'

Sep 16, 2022

It seems that most of us with 38/38 or 32/36 Webers experience dry carb float bowls if our car sits for a relatively short period of time (>4 days?). I've put up with this for a year or two, but it's annoying and tough on the starter and battery and time to address the problem.

I've owned many collector cars with carburetors. Some had the same problem, some didn't. I could never figure out a common thread for those that did. New, rebuilt, old...it didn't seem to matter. Some did, some didn't. I could never pin down where the fuel was going. It couldn't be backing out of the carb up...

• Dick Steinkamp
• Replies: 69
• Forum: E3 Sedan Projects and Restorations

 

[jmackro]

Wouldn't this cause a full-time restriction? Mechanical pump would have to pull harder through it, no?

In theory you're right. And more restriction creates more opportunity for vapor lock. But in practice, a diaphragm-type pump (the ones that go "clickety-click") have two, one-way valves that keep fuel moving in the right direction. Those valves don't create much resistance in the tank --> carburetor direction (though ∞ resistance in the carburetor --> tank direction).

With a rotary-type pump, there may be more resistance. You can install a one-way valve in parallel with the pump, oriented with the direction of flow toward the carburetors. That way, the mechanical pump can pull fuel through the one-way valve, but when the electric pump is running, the fuel can't flow back into the tank. See photo below (thanks to whoever I stole this picture from), I have a similar set-up in my coupe, which allows me to just run the e-pump for a few seconds to prime the carbs when I start the car after a few days of non-use, but use the mech. pump the rest of the time.

I would love to figure out the best setup to implement and am seeing lots of opinions (ie cylinder electric fuel pumps vs a boxy Facet fuel pump), various kill switches, and relocation spots (trunk, relocating within the engine compartment, etc).

You definitely don't want it in the engine compartment. The cause of vapor lock is trying to pull fuel upward and over a long distance. And fuel doesn't know whether it is being pulled by a mechanical or an electric pump. In other words, the fact that you have a mechanical pump isn't the problem - it's the location of the pump that causes the vapor lock.

 

[bavbob]

Why thank you! Note the pump is in parallel and not series. I had a lock in series and the parallel setup is the one the maker recommends.
I have no issues with my Bavaria...........I kept the Zeniths

 

[Ohmess]

I am running a pierburg pump just like this one - http://www.piercemanifolds.com/product_p/99009.131.htm - along with a Bosch (VW I think) inline filter installed in the trunk.

My pump is attached to the subframe using the rubber isolation mounts, near where Stevehose has his (https://e9coupe.com/forum/threads/final-word-on-electric-fuel-pump-for-carbs.22574/post-165257).

I've also installed the revolution electronics relay, which pumps three seconds of fuel to fill the bowls when first powered up, and will kill the pump if it does not get a signal from the coil that the car is running. https://www.revolutionelectronics.com/Products/Fuel_Pump.html

I've never had vapor lock problems.

 

[jmackro]

I've also installed the revolution electronics relay, which pumps three seconds of fuel to fill the bowls when first powered up, and will kill the pump if it does not get a signal from the coil that the car is running. https://www.revolutionelectronics.com/Products/Fuel_Pump.html I've never had vapor lock problems.

I'm wondering if 3 seconds of pumping is enough to really fill the carburetor bowls if the car hasn't been driven in awhile. It sounds like your mechanical pump does the "heavy lifting", with the exception of the first three seconds after the ignition is turned on. I primarily use my mechanical pump, and have never had problems with vapor lock either. Maybe Steven's (this thread's originator) mechanical pump is on it's way out, which led to his V.L.

 

[Ohmess]

Jay - My only fuel pump is the little Pierburg. I pulled the mechanical pump to make room for the Triple Webers.

 

[Stevehose]

I'm wondering if 3 seconds of pumping is enough to really fill the carburetor bowls

You can just turn the key off and on again for another 3 seconds ad infinitum. My Carter pump throws a lot of fuel so I would say 2 cycles is more than enough for dry bowls, although I don't think DCOE's are as prone to that as say the downdrafts are. WIth the side drafts and that pump I've never had a vapor lock in very hot climates or any start issues after a long sit.

 

[jmackro]

Jay - My only fuel pump is the little Pierburg. I pulled the mechanical pump to make room for the Triple Webers.

OK, now I get it. I guess triple Webers crowd out the mechanical fuel pump. As long as your Pierburg is mounted down low, I wouldn't expect you to have vapor lock problems.

I don't think DCOE's are as prone to that as say the downdrafts are. WIth the side drafts and that pump I've never had a vapor lock in very hot climates or any start issues after a long sit.

I have Weber 32-36's on my Coupe and the fuel does evaporate after a week or so. But I have Weber DCOE's on my Alfas, and they too would require a lot of cranking after an extended (e.g., a week) period of non-use, back when they had mechanical pumps. They have long since been upgraded to e-pumps. My sense is that all carburetors have their fuel bowls open to the atmosphere, so their fuel will evaporate after several days.

 

[HB Chris]

The fuel in my Zeniths on both e3 and e9 will fire quickly after two weeks sitting. Downdraft Webers as superior are a myth in my mind, especially since their throttle linkages are a poor compromise on many, the CSL I drove is like an on/off switch, not fun.

 

[Stevehose]

The fuel in my Zeniths on both e3 and e9 will fire quickly after two weeks sitting. Downdraft Webers as superior are a myth in my mind, especially since their throttle linkages are a poor compromise on many, the CSL I drove is like an on/off switch, not fun.

Agree, I try to talk people out of swapping Zeniths for Weber downdrafts at every opportunity. Back in the 80's after I swapped them my linkage promptly locked open, and had an obvious loss of top end. My sidedrafts fire at the first touch of the crank > month whether I fill the bowls or not. Perhaps the less dry climate in FL vs CA has something to do with it, or that I use tiny foam filters for the idle jet circuit/bowl vent hole on the face of each carb.