Lotsa Pumping Needed On My 79

[speedracer]

So I get in my carbureted 79 Spider after it has sat for about a week, and I have to pump the heck out of the gas pedal before she'll kick over. I need to do that whenever she has sat around for awhile. I don't have that problem when I use it daily or near daily. I know, I know, the obvious answer is to use it daily!

But what causes this? Seems like the gas goes all the way back to the tank during the downtime and needs to be pumped from there instead of it staying in the gas line. Isn't there a check valve in there to prevent this

[So Cal Mark]

gas is probably leaking out of the accelerator pump diaphragm

[sptcoupe]

Check the accelerator pump diaphragm as Mark says, then swap out you mechanical pump fir an electric pump and this problem will be gone forever.

[bradartigue]

Check the accelerator pump diaphragm as Mark says, then swap out you mechanical pump fir an electric pump and this problem will be gone forever.

This isn't a fix at all, it is overcoming the failure of one part with another part, in this case, a worn out component on the carburetor being compensator for with an electric fuel pump. Fix the actual problem(s) because there is absolutely nothing wrong with the mechanical pumps.

[speedracer]

It seems like your all in agreement on the accelerator pump diaphragm is the problem. My fuel pump does seem to work fine, and I've had no problems with it, but I'd like to hear more opinions from members on mechanical versus electric pumps.

Now, where exactly is the accelerator pump diaphragm located?

[bradartigue]

I'll continue my opinion then - there is no point in using an electrical pump unless the car originally had one, and I'd question that as they only had them for a year or so. In a car that everyone derides the electronics and bitches when they are changed this idea is to change the pump to something else. It's hypocritical. The electric pumps add a small but additional load to an already overloaded system, they create yet another splice in an already spliced up fuel line, and what most people here are using for pumps are the most worthless unregulated piece of crap you can put in your car. That's the square facet pump.

If you go the electric route then get the right pump, a Bendix type, internally regulated pump at 3psi, they cost about $120 from any Alfa Romeo shop.

I just don't see the purpose; people who swapped mechanicals for electrics "because they failed" are typically swapping out a 20+ year old pump and acting like its a piece of crap. If you put another mechanical on it you'll probably get 20+ years out of it. Well, with ethanol fuels 15.

[tartan18]

When I bought my car it had the Facet square electric fuel pump mounted in the engine bay. I took it out and replaced it with a mechanical pump because the car frequently showed signs of fuel starvation. The only problem I have encountered is that I occasionally experience vapor lock. I use only 92 non-ethanol premium gasoline. My car is a 1975 with a DFEV 32/36 carb. The carb has one half inch spacer.

I now wonder if I have the correct mechanical fuel pump or whether changing back to a high quality electric pump is the best way to solve the vapor lock issue. I question if I have the right mechanical pump because the first pump I ordered didn't work -- it didn't mesh with the auxiliary shaft lob.

[majicwrench]

Brad and I differ once in a while, on this I couldn't agree more. To do a hack job of installing an electric pump, create more wiring issues, fuel leak, yuk. FIx the problem. Yes, accel pu,mmp diaphram can leak letting fuel drain when it sits. Is it the issue?? You need to look. Accel pump is on side of carb facing L fender. Square houising four small bolts. Fuel should not be present under this thing stick your finger under there. Mechanical pumps have a flapper valve so fuel can't drain back. Often stuff under valve letting fuel in line drain back.
Fuel cannot really "drain back" from carb although it can evaporate,from the heat of a hot engine after shutdown.

I cleaned the flapper valve in fuel pump in my 72 3-4 years ago, what a difference.
Keith

[bradartigue]

Brad and I differ once in a while, on this I couldn't agree more. To do a hack job of installing an electric pump, create more wiring issues, fuel leak, yuk. FIx the problem. Yes, accel pu,mmp diaphram can leak letting fuel drain when it sits. Is it the issue?? You need to look. Accel pump is on side of carb facing L fender. Square houising four small bolts. Fuel should not be present under this thing stick your finger under there. Mechanical pumps have a flapper valve so fuel can't drain back. Often stuff under valve letting fuel in line drain back.
Fuel cannot really "drain back" from carb although it can evaporate,from the heat of a hot engine after shutdown.

I cleaned the flapper valve in fuel pump in my 72 3-4 years ago, what a difference.
Keith

Holy crap we agree! And there was much rejoicing...

I doubt you have fuel starvation (in the sense of no fuel) with a mechanical pump - the demands of the DFEV even at WOT aren't enough to drain the bowl when it is being filled at 2-4psi (the nominal range). I'd check the main jets for being too small or the setting of the float, you might not have enough fuel in there to begin with.

Of course it can be a bad diaphragm in the pump, if the thing is weak you'll vapor lock, but once running it won't stop. That pump photographed isn't OEM, but I don't know if you can get a FIAT pump any more.

[speedracer]

Accel pump is on side of carb facing L fender. Square houising four small bolts. Fuel should not be present under this thing stick your finger under there. Mechanical pumps have a flapper valve so fuel can't drain back. Often stuff under valve letting fuel in line drain back.
Fuel cannot really "drain back" from carb although it can evaporate,from the heat of a hot engine after shutdown.

I cleaned the flapper valve in fuel pump in my 72 3-4 years ago, what a difference.
Keith

Thanks for the help in locating the accelerator pump. Will look at it. If it's not that, then I will check the flapper valve on the fuel pump. Could just be a build-up of gunk or junk blocking it's operation, thereby letting the fuel drain back, is that correct?

Good info, thanks!

[majicwrench]

In old fuel pumps you could take em apart and fix flapper, not sure in new pump. Basicly if you can blow back thru pump it aint right. Either valve is not working or not there (cheap pumps)
Mine just had general junk under it. First year w my 72 had to crank crank crank crank crank if it sat for a day or two. Put a hunk of clear line in fuel line and watched it drain away. Fixed flapper car is sooooo much nicer.