Yay or Nay Electric Fuel Pump

DougE

DougE

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Happy New Year everyone, I have a 1972 e9 with 32/36 Webers. I don't drive the car often enough, as a result after a couple of weeks I have to crank the engine too long before it hits and runs. I think the problem is that the manual fuel pump has to work extra hard to bring fuel to the carburetors.

I'm not a huge fan of electric pumps, I was thinking about installing a Pierburg or Carter Rotary pump at the tank with a momentary switch to bring fuel to the manual pump. Has anyone done something similar or any suggestions would be appreciated?

Cheers, Doug
 
maybe install a one-way check valve near the carbs to avoid drainback?

Do webers not have fuel bowls that keep fuel in them? No clue.
 
I use the lift pump out of a 633csi to supply my Webers. It produces about 3# of pressure and enough volume to support more power than my 3.5l motor makes. It mounts quite nicely in the Bav tank.
 
fuel pump...

encourage you to try check valve, even a week of just a hose clamp on then off when you want to start your car, to show you the effect of a check valve. Then decide. pretty simple fix. Save your efforts for something else, unless you are bent on electric pump. Mike
 
Yes, dropping in an electric pump is a lot of work, if a simple solution like a check valve works then worth a try first.

bluecoupe30! said:
encourage you to try check valve, even a week of just a hose clamp on then off when you want to start your car, to show you the effect of a check valve. Then decide. pretty simple fix. Save your efforts for something else, unless you are bent on electric pump. Mike
Click to expand...
 
Factory check valve is cheap....


Part number is 16 14 9 068 988 and cost about $9.00 from the dealer.
 
I think the fuel does evaporate out of Weber float bowls over time. If I leave my car sitting a while, I will have to use the electric fuel pump to refill the bowls before cranking. My fuel pump has a built in check valve so it's not drain-back.

Cheers
James
 
I had used one of those cheap little electric square fuel pumps, located in the gas tank well of the trunk, back when I was running Weber 32/36s on my 3.5 liter engine. Then I upgraded to Weber 38/38s and I spent way too much time and money trying to get the jetting just right. WAY too big a flat spot that I just couldn't solve.

One of the suggestions from this site was to change fuel pumps, so I started my research. Seems that cheap little fuel pump puts out high pressure but low volume, just the opposite of what the Webers wanted. So I switched to a Carter fuel pump, low pressure and high volume, and mounted it under the car next to the fuel tank.

This solved 95% of the flat spot problems, and I've almost gotten the jets dialed in to perfection!
 
+1 Check valve. Most of the electric pumps have them built in, kind of a clue there.
 
bavbob said:
+1 Check valve. Most of the electric pumps have them built in, kind of a clue there.
Click to expand...

And all mechanical pumps have a built-in check valve - that's how they work! Otherwise, as the diaphragm built pressure in the pump cavity, the fuel would just flow back into the tank.

I guess the check valves in fuel pumps don't seal 100%. When you leave the car sitting for a week or so, the fuel slowly drains past the valve. The fuel in the carbs also evaporates, which even a 100% effective check valve isn't going to solve.
 
Now that the topic has come up, and with a CS that sees very little use, I have to ask why or more to the point HOW, fuel can drain back through the pump.

I'm familiar with the concept of a siphon, and acknowledge that the carbs are higher than the tank. BUT, the discharge from the pump passes the float needle valve (a one-way valve) and doesn't fill the float chamber, thus providing an air gap. A siphon shouldn't work if there is an air gap. Add to this that the check valve in the stock pump should (also) prevent gas from siphoning back to the tank.

Yet in all the years I've had this CS, it has always been the case that if not run for several days, it will be slow to catch and run. Opening the hood and priming with an ounce in one or both carbs us enough to run the few moments it takes to draw gas from the tank. Daily driving, no problem.

How say we all, what is the reason for this?
 
I believe that evaporation is a bigger factor than draining. As Charlie points out, the carb reservoirs can't drain or siphon back.
 
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Love my electric pump/non stock set up.

Get in, flip switch, hear fuel flow from rear of car, fill empty webers....then turn key and go even after weeks of slumber.

#1 in belief that fuel evaporates from Webers in a week or two of non-operation.
 
Jmacko, I though the evaporation explanation might come up, but that requires the fuel to vaporize in the float bowl, and then exit the carb through... what? A tiny vent opening (I think there's one on the top section somewhere). The only "pressure" for this to happen is the vapor pressure of the gas, which is slight. I have a hard time imagining 3-4 ounces of fuel will evaporate through that vent opening within about a week.

Doesn't the lack of fuel after a week happen also to those in much colder climes than my local upper-70s to mid-80s also, which would mitigate against evaporation?

All in all, "they all do that" seems the most plausible. Just another mystery of coupe ownership. Or is it the secret handshake, and a la Dan Brown, we're on to something here?
 
Honolulu said:
Jmacko, I though the evaporation explanation might come up, but that requires the fuel to vaporize in the float bowl, and then exit the carb through... what? A tiny vent opening ..... "they all do that" seems the most plausible.
Click to expand...

I see your point: how could that much fuel evaporate so quickly? And why aren't the evaporation rates markedly different summer-winter? But as you note, "they all do that", so the fuel is disappearing somewhere. Into a black hole? Dark side of the moon?
 
I think you're on the right track regarding the built in check valve or proper operating of the pump, when I had 2 Zeniths it would start up regardless of down time so it can be done. I made sure my pump was new.

But if evapration is slow then there should be some fuel left that can be pumped in pre-start via the accel pumps.

jmackro said:
I see your point: how could that much fuel evaporate so quickly? And why aren't the evaporation rates markedly different summer-winter? But as you note, "they all do that", so the fuel is disappearing somewhere. Into a black hole? Dark side of the moon?
Click to expand...
 
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