Mechanical Fuel Pump Back Flow Question

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mr2m1

mr2m1

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I have a 2F with a Weber carburetor and DUI. When starting my cruiser cold it takes about 15-20 cranks before the pressure builds up to get fuel into the carburetor. Unfortunately this is reducing the life of my battery. It will on the first crank after It has warmed up. I should note that I have de-smogged the engine as well.

Any ideas on how to keep pressure in the fuel lines? I'm not against adding an electric pump if that would fix the problem. I just like the reliability of mechanical over electric.

Thanks,
Jason
 
mr2m1 said:
I'm not against adding an electric pump if that would fix the problem. I just like the reliability of mechanical over electric.
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Perhaps do both? Maybe add an in-line electric pump back near the tank with a dash mounted toggle switch. Run it for a few seconds before a cold start, turn it off once the engine is running.
 
I second what @bhsdriller asked. Is the choke hooked up? Should be an electric choke unless it was converted to manual. When I ran a Weber when living in TX I never needed the choke (I disabled it manually). Fired up cold and hot, didn’t matter. Also, it sounds like you know the fuel pressure; I want to ask if you’re running a fuel pressure regulator. @mr2m1
 
klinetime574 said:
I second what @bhsdriller asked. Is the choke hooked up? Should be an electric choke unless it was converted to manual. When I ran a Weber when living in TX I never needed the choke (I disabled it manually). Fired up cold and hot, didn’t matter. Also, it sounds like you know the fuel pressure; I want to ask if you’re running a fuel pressure regulator. @mr2m1
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Yes. I have an electric choke. I also have a pressure gauge near the carburetor. I didn’t think about checking that before starting it to see if there is any pressure in the line.

I’m wondering if it has anything to do with the emissions left on the vehicle. I still have the charcoal canister and the plastic manifold thing near the fuel tank inlet. Perhaps it’s not sealed and allows air back into the fuel line?

I don’t know I’m just throwing ideas out there.
 
mr2m1 said:
Yes. I have an electric choke. I also have a pressure gauge near the carburetor. I didn’t think about checking that before starting it to see if there is any pressure in the line.

I’m wondering if it has anything to do with the emissions left on the vehicle. I still have the charcoal canister and the plastic manifold thing near the fuel tank inlet. Perhaps it’s not sealed and allows air back into the fuel line?

I don’t know I’m just throwing ideas out there.
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I still have my charcoal canister, even with Sniper set up. I left the lines as I had them when running a carb; tank and purge swapped (desmogged).

Not sure what you mean by manifold thing near the fuel tank inlet. Maybe the fuel vapor thing in the passenger rear quarter panel? I’ve never touched mine FWIW.

To clarify: I said regulator, you said pressure gauge. The regulator limits the amount of fuel going into the carb. The gauge only measures it.

IIRC Weber says 3psi max. Too much fuel could cause a hard start when cold. Although, an operational choke when cold (that may not be needed) may also cause a hard start. Or a combination of both LOL.

HTH
 
klinetime574 said:
Not sure what you mean by manifold thing near the fuel tank inlet. Maybe the fuel vapor thing in the passenger rear quarter panel? I’ve never touched mine FWIW.
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Yes, the fuel vapor thing. I thought maybe that had something to do with losing pressure in the fuel line.
klinetime574 said:
To clarify: I said regulator, you said pressure gauge. The regulator limits the amount of fuel going into the carb. The gauge only measures it.
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I have both near the carburetor, a pressure regulator and gauge to check the fuel pressure.
klinetime574 said:
IIRC Weber says 3psi max. Too much fuel could cause a hard start when cold. Although, an operational choke when cold (that may not be needed) may also cause a hard start. Or a combination of both LOL.
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I will check to see if fuel is getting to the bowl after a couple of pumps from the mechanical fuel pump this weekend, if it is then it could be choke issue.
klinetime574 said:
HTH
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I seem to remember on a hot start it would fire up with no pumping of the gas pedal. Cold start was 2-3 pumps. Both scenarios with no choke applied. I think it was the same with Weber and Aisin carbs.
 
Okay, I just ordered an inline fuel pump from tpi4x4.com, I can use this with my mechanical pump. I will post my results after its installed.

Thank you for your responses.

Screenshot 2025-11-15 100234.webp
 
do not use an electric pump and mechanical pump, one or the other,
as stated above you need to figure out if there is gas when starting
 
mr2m1 said:
Can you explain why? From what I'm reading you can use both.
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if you want to use, go for it, but I wouldn't.

if the mechanical pump fails, you will fill the crankcase with gas
to me, using an electric pump in addition to a mechanical pump is masking/hiding the real issue
there should be no reason for the electric pump
there are many, many 60's out there running just fine on a mechanical pump only with either stock carb or weber carb.
 
3_puppies said:
do not use an electric pump and mechanical pump, one or the other,
as stated above you need to figure out if there is gas when starting
Click to expand...

I've seen it in the case of not driving very often where they use an electric on a switch to fill the bowls instead of cranking and cranking. Then shut it off, start and then the mechanical is working as normal.
 
3_puppies said:
if you want to use, go for it, but I wouldn't.

if the mechanical pump fails, you will fill the crankcase with gas
to me, using an electric pump in addition to a mechanical pump is masking/hiding the real issue
there should be no reason for the electric pump
there are many, many 60's out there running just fine on a mechanical pump only with either stock carb or weber carb.
Click to expand...
Any idea why I'm getting back flow out of the line and have to crank the engine over 10-15 times? I would like to stay with the mechanical pump only, but I'm draining batteries well before their time.
 
bhsdriller said:
I've seen it in the case of not driving very often where they use an electric on a switch to fill the bowls instead of cranking and cranking. Then shut it off, start and then the mechanical is working as normal.
Click to expand...
I like this idea, will gas still flow thru the electric pump to the mechanical pump if the electric pump is switched off?
 
mr2m1 said:
Any idea why I'm getting back flow out of the line and have to crank the engine over 10-15 times? I would like to stay with the mechanical pump only, but I'm draining batteries well before their time.
Click to expand...

are you sure that is your problem?
IIRC the mechanical pump has a check valve on the out flow port, maybe that has failed if in fact you don't have gas to the carb right away when cranking.
I would remove the inlet to the carb, have someone crank it and see if there is gas right away, or check at the inlet of the regulator.
 
3_puppies said:
are you sure that is your problem?
IIRC the mechanical pump has a check valve on the out flow port, maybe that has failed if in fact you don't have gas to the carb right away when cranking.
I would remove the inlet to the carb, have someone crank it and see if there is gas right away, or check at the inlet of the regulator.
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Thank you. I will look for a check valve and check to see how many cranks it takes to get fuel to the carb. Its possibly the valve was removed when it was de-smogged.
 
mr2m1 said:
Thank you. I will look for a check valve and check to see how many cranks it takes to get fuel to the carb. Its possibly the valve was removed when it was de-smogged.
Click to expand...

it would be internal in the fuel pump and the later 3 port fuel pump is not serviceable
it would be a replacement, don't forget about the spacer
 
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