dual tank fuel system operation questions

75k20

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would i be able to use an electric fuel pump to prime my carb after my truck has been sitting for a while? i purchased the small edelbrock 38gph electric fuel pump. i don’t think my pump is bad because there is no gas in the oil from what i can tell.

is there any benefit to using the return line from my mechanical pump? right now it is plugged off

i replaced the plastic fuel filter i had with a standard parts store metal filter and a fuel pressure regulator. the regulator is about 2 or 3 inches from the carb inlet. is this a long enough distance for the fuel pressure to be correct?
 

SirRobyn0

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You should be able to run a primer pump, I'm really not sure about the factory tank switches, but all the aftermarket ones I've seen have been approved for low pressure pumps IIRC 10psi or less kind of deals.

The return line helps keep fuel flowing before the pump and in the pump mainly to prevent vapor locking. Personally I'd want it functional, but if the switch valve isn't setup for it and the plumbing isn't there, then perhaps the thing would be to get a pump without the return line.

But there is no reason you should need a primer pump. I'd be taking a close look at that mechanical pump. I'd be willing to bet that it is weak.
 

fast 99

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Never got an official explanation why later models have a return and early ones didn't. Assuming the above reason is correct, avoiding vapor lock. Vapor lock is more of an issue today than it ever was back in the day. Low octane and ethanol fuel will boil easier. Fuel today is NOT formulated for a carb. I would run a return if at all possible. I previously posted on the saga of replacement mechanical pumps. Might want to look that up, it could save you some grief.
 

SirRobyn0

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Never got an official explanation why later models have a return and early ones didn't. Assuming the above reason is correct, avoiding vapor lock. Vapor lock is more of an issue today than it ever was back in the day. Low octane and ethanol fuel will boil easier. Fuel today is NOT formulated for a carb. I would run a return if at all possible. I previously posted on the saga of replacement mechanical pumps. Might want to look that up, it could save you some grief.
Well IDK If you'll ever get an official explanation but my understanding is with the advent of air pumps, and running base timing at idle, all this was done to increase heat in the exhaust manifold to help anything not burned in the combustion chamber to burn off. Also helps to get the cat up to and keep it at operating temp, if the vehicle is equipped. This all adds extra heat to the lines and fuel pump. So I think but do not officially know that, that is the reason. I'll tell you though I had a buddy with a 72 C30 - 350 no return line and when we'd take that thing out into the field on an 80F+ we were guaranteed at least one vapor lock. More if it was hotter. We'd carry water to pour on the pump and lines to get it going again. And this was in the late 90's, if time frame matters. My 84 with 305 and a return line, I can drag my trailer around fields and idle it all day in 90F+ weather and it never vapor locks. So maybe the return line was more a function of fixing a problem? IDK for sure I just know these trucks benefit from a working return line.
 

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Have a friend who fought a vapor lock issue on a class a 70's Chrysler 440 motorhome. New pumps wouldn't fix it, no return line. Fuel had to travel much further than a pickup and that probably exacerbated it. Only solution that worked with was a very low-pressure 3 lb electric pump near the tank.
 

SirRobyn0

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Have a friend who fought a vapor lock issue on a class a 70's Chrysler 440 motorhome. New pumps wouldn't fix it, no return line. Fuel had to travel much further than a pickup and that probably exacerbated it. Only solution that worked with was a very low-pressure 3 lb electric pump near the tank.
Yes that will help. There is a fuel filter I'd have to look for the part #, but it has a built in return line, so we use to just add the filter in after the pump, and plumb the return line. I preferred that to the electric because of to many electric pump failures. We did that on the Chrysler motorhomes.
 

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