69 nova

ok I built a carb 6.0 66 nova. I ran two 3/8 lines when car was on rotisserie I also installed a Mallory 140 pump with bypass regulator So I have it running now and my pressure is all over the place even lost all pressure. I think my return should be bigger for that pump. I really don't want to redo all my lines what pump and regulator would be good with 3/8 6an fees and return ??? And can I return to pump with a Y fitting or does it need to go directly to tank ??

LQ4BU

As far as I know, the return line should always go back to the tank, and for optimum performance it needs to be submerged in the fuel and not spraying down from above.



How much horsepower is your LS? A lot of guys do not run a return line.


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69 nova

I have stock tank 3/8 sending unit it's a lq4 with 243 and a tick sns stage 2 cam with victor jr and a 750 holley

Pop N Wood

iTrader: (1)

Your fuel lines are more than adequate. I ran that exact set up for the last 8-10 years with no fuel pressure issues. Mallory 140 pump, 3/8 hard lines for source and return, Mallory return style pressure regulator, quality AN6 connectors.

You have some other problem. A leak on the inlet line before the pump will cause what you are seeing. A bad pressure gauge will as well

Full disclosure, I am in the process of replacing the Mallory pump. Had nothing but troubles with that unit. Two weeks after getting the car on the road the pump seized up with tank debris. Figured my bad for not cleaning the tank prior to the swap. I did have a prefilter but guess it didn't work. The gerotor design of the Mallory unit is less tolerate of debris than a standard rotary vane, hence the 40 vs. 100 micron prefilter.

Swapped in a generic Summit 140 gph pump for a couple of years with no issues. Same flow rate as the mallory. Got paranoid about dirt and added a better quality 40 micro prefilter and super sized Fram HPG-1 five micron canister filter prior to the carb.

After a couple of years sent the Mallory back to the factory and got it rebuilt. Ran that for a few more years and then just last month something went wrong in the motor causing it to blow fuses. Have an Aeromotive SS sitting on the bench waiting for some shock mount isolators from McMaster Carr to finish installation.

Sending the return line to the bottom of the tank so it doesn't aerate the fuel is not a bad idea, but i run that way so like said above just not optimal. Installing the fuel pump near the tank with the bottom level with the bottom of the tank is more important. Minimizing restrictions in the suction line prior to the pump is even more important. I run 1/2 line and an AN8 low loss prefilter on the inlet side. Make 100% sure all connections are tight in suction line path.

Pop N Wood

iTrader: (1)

By the way easy way to check if the return line is big enough is with the motor off and pump running fully open the regulator and read carb inlet pressure gauge to measure the back pressure through the return line. Want less than 2-3 psi back pressure.

69 nova

Mine won't go below 6 with screw out of regulator

69 nova

But I do have a Y on my feed line with a dead head regulator for my nitrous and the the other bypass is feed from other side of Y I'm wondering if that is causing my problems

ZONES89RS

iTrader: (25)

I'd try a different pump and regulator. I've run 3/8 feed and 5/16 return with no issues.

69 nova

I plan plan on getting a new pump and regulator any one have any good suggestions on what brand ??

Pop N Wood

iTrader: (1)

Just read your initial post. You have a Y down stream of the pump with one side going to a dead head regulator to the nitrous and the other side going to your return style regulator/carb. The return line than goes where? Back to a T on the suction side of the pump?

Back into the tank is definitely the best.

Aeromotive street strip seems to be the pump of choice. expensive but hopefully reliable. Cheaper than a tow home, that is for sure.

I have a mallory 4309 regulator. Not had any issues with that.

jerr6

iTrader: (1)

this could be a issue when using nitrous. won't the fuel system default to whatever the bypass reg is set to? say you have 6psi on bypass reg to carb and 7psi to dead head reg won't the bypass only let pressure go to 6psi ?

69 nova

Comes from 3/8 sending unit goes to cartridge fikter then threw pump up to engine bay to a Y one side to a dead head other to bypass the return is going into my fill tube

nawlins-tim

Carb set up takes a much larger return. A good source of info is on aeromotive web site. They recommend same size Feed and Return. Depending on your needs. Recently bought a AEM intank pump and they recommend one size smaller for your return than feed. Another thing to consider is a Quality regulator if you are trying to use a high pressure pump on a carb set up.