Fuel system problems for 76 chevy

[7387chevynut]

First off...............Fuel sytems and electrical are not my thing.



My 76 Chevy K20 has been giving me problems over the past 2 years. The carb that was on it was rebuilt by my brother, and I do trust his work, but 2 yrs ago when it installed it, the truck would start up, run rough, backfire, and pump fuel outside of the carb, and as soon as you let off the gas it stalls out.

Last year, I didnt Fk with it...........just turned over the engine to keep everything lubed.


Today I swapped over the carb off my 67 K20............(which runs fine)...............over to the 76 K20................and the same FKIN problem over again.................runs rough, backfires, pumps out gas..........and as soon as you let off the gas it stalls out.



I dont get it.............all I can think off is that its gotta have something to do with the gas tank/fuel lines or sending unit??


What do you guys think?

[85cHeavyMetalBogger]

where is gas pumping out ffrom when you say its pumping gas out

[Jjay78]

to much fuel pressure, you need a regulator

[4x4xdodgeman]

need more info on your fuel system!!! start at the tank and tell us what you have and go to the carb.

[KORNBREAD]

how old is the mechanical fuel pump?

[Disturban]

need more info on your fuel system!!! start at the tank and tell us what you have and go to the carb.

X2, if you have a electric fuel pump it is probably giving the carb too much fuel pressure and it need and adjustable fuel pressure regulator.

[old school truck dude]

  Where does the backfire come from, intake or exhaust..? Sure sounds like too much fuel pressure since it does the same thing with 2 different carbs  which Im assumin are quadrajets?

[7387chevynut]

Where does the backfire come from, intake or exhaust..? Sure sounds like too much fuel pressure since it does the same thing with 2 different carbs  which Im assumin are quadrajets?

truck has a Q-jet on it now.........both carbs I 've used are Q-jets. As to the back fire........its hard for me to tell while sitting in the truck....trying to keep it running........but it sounds like its coming from the exhaust.

The current carb was leaking fuel out the left side (choke side) 1/2 way up, and the leaking fuel out by the excellorator pump..................but again......this carb was off of my 67 K20 and it ran fine on that truck.

Truck has a mechanical fuel pump on it, thats about 4yrs old.

Also, I've never heard of fuel pressure regulator on the carbed truck............since it never had one in the 6yrs I've owned it.  I know the carb has set screws on the front of it to adjust fuel flow to the carb.....but I havent messed with those.

In 2007 I put a brand new gas tank in the truck, pretty sure the lines got hooked up properly

[old school truck dude]

Have you tried takin the gas cap off? Maybe not vented properly and buildin up pressure in this heat.. Is there a filter between the pump and the carb? You cant rely on the little one in the inlet fitting of the carb because it has a spring behind it so that if it gets clogged completely it gets pushed off its seat and allows dirty fuel into the carb. You should be using a large inline aftermarket filter and toss the little filter and spring in the weeds. If this truck has been settin up, chances are the fuel is sour and/gelled and may have rust in it. That would cause immediate floodin no matter what carb you put on there. I would clean out the bowl and accelerator pump of the original carb, pump some fresh fuel into a gas can or whatever through the pump. You can hook your suction line up to a  boat tank or somethin real clean, hook the carb back up usin the new inline filter, and see how that works. Might have to flush or replace the tank. If its backfiring out the exhaust, that usually means too much fuel, its gettin raw fuel into the exhaust.. Could also mean the valve timing is off, check the cam/crank/distributor position maybe the chain slipped.

Question: Did it ever run right after you put the new fuel tank in it..? Also, why was the carb rebuilt?

[7387chevynut]

Question: Did it ever run right after you put the new fuel tank in it..? Also, why was the carb rebuilt?

Truck didnt run right after the new tank was swapped in. carb was rebuilt thinking that ( IT )was the cause of the problem


I am wondering if its the gas tank, because that tank........while it was brand new and I only paid 25.00 for it.......was for a 87 model year chevy truck which is fuel injected.................now I wonder  if that would pose any problem??..............but I fail to see why it would because the  tanks look identicle to 73-86 tanks.

[Jjay78]

it really sounds to me like your getting to much fuel pressure matt, is the fuel pump in the tank getting power? if it is cut it and that'll solve your problems... i had an issure like this with an old car of mine, and cutting the fuel pressure fixed it. for a carb all ya need is 5 to 9 psi

[7387chevynut]

it really sounds to me like your getting to much fuel pressure matt, is the fuel pump in the tank getting power? if it is cut it and that'll solve your problems... i had an issure like this with an old car of mine, and cutting the fuel pressure fixed it. for a carb all ya need is 5 to 9 psi

no fuel pump in tank......truck is a 76......mechanical fuel pump on motor. The GAS TANK I installed in it........brand new.....is for a 87 chevy......and I am wondering if that doesnt have to do with my problems.............but if it does......I am failing to see how.

[4x4xdodgeman]

what year sending unit did you put in the tank?   

[7387chevynut]

what year sending unit did you put in the tank?   

I resused the sending unit from the old tank that I took out.

[Jjay78]

does your fuel pump have the excess fuel return line on it?

[old school truck dude]

does your fuel pump have the excess fuel return line on it?

Now theres a real good question! If it dont, it sure needs one! and it needs to be hooked up correctly, some folks plug them off. This is startin to sound like its got to do with the lines.. Might want to drop the tank back down, pull the sending unit, and see exactly which line is which - one of them is excess fuel return, one is the pickup, one should vent to somethin - I wonder if that year had a charcoal canister..?

[Jjay78]

i've seen some pumps that only have the feed and the output to carb lines on them, and nothing but trouble with them, i think it's an 84 trans am that is the easiest look up to get the pump with the return line, if your new pump doesn't,

[7387chevynut]

does your fuel pump have the excess fuel return line on it?

Now theres a real good question! If it dont, it sure needs one! and it needs to be hooked up correctly, some folks plug them off. This is startin to sound like its got to do with the lines.. Might want to drop the tank back down, pull the sending unit, and see exactly which line is which - one of them is excess fuel return, one is the pickup, one should vent to somethin - I wonder if that year had a charcoal canister..?

Good question, if I remember right, the old fuel pump had a 3 line fitting because the truck had dual tanks..........when I swapped in the new tank and did away with the right side tank (because it had a leak in it) My brother told me to get a new fuel pump with a 2 line fitting on it because the truck only has 1 tank now.......................so what jay and old school are asking might be adding up to somthing.   Also I am quite certain that truck has a charcoal canister......most older chevys had those.

[Jjay78]

that's probly your problem bud, the pump can't send the excess fuel back to the tank, it can only go to the carb, get one with the return line and ya should be all good

[Jjay78]

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