crackenzag

my 81 vette has a problem. the fuel goes straight through the fuel pump and back to the tank instead of going up to the carb. The line between the pump and carb is clear. if I pinch off the return hose, it will run great, but fuel pressure goes above 10 psi... is there a restrictor or something in the return line that prevents the fuel from just going back to the tank such as in a fuel injected system (fuel pressure regulator in the return side of the fuel system).

this one has me stumped

SIXFOOTER

There is supposed to be a restriction in the return line port. Someone will pipe in on what size, you may just need a new fuel pump

shafrs3

Is there a filter on the carb that's clogged?

gkull

Your internal pump regulator bypass is bad. What is going on is: The AcDelco pumps have a simple pressure relief bypass of some sort(return to the tank)to supply the carb with a constant pressure usually 5-6 psi. The pump can put out 10 psi as you see with the return closed. The bypass should be returning the extra 4 psi to the gas tank

Just go down to NAPA and buy a new one.

crackenzag

I replaced the pump already. same problem. I did not use a delco pump. is it possible that the "aftermarket" pump i installed does not have the "restriction"? Do i have to use a delco pump? if so why do they even make a pump that they know will not work?

oh yea, and i put a new fuel filter in the carb. it is a rollover filter with the valve in it and it is installed correctly.

Matt Gruber

i sawed open the pump from a 76.
has 1/16" restriction

crackenzag

ok, i dont' have a local napa store and orielly can't get me an ac delco pump for the carb'd vehicle. I ordered a pump from the dealer. if this don't work, I'm SOL...... if anybody else has anything to add to this I'd appreciate it. even if it's an agreeance with someone else.

...Roger...

OK this really high tech.Here is a pic of the inside of the pump can.The largest hole is the input from the tank dont worry about that one.The hole at the bottom of can goes to the carb the tiny hole in the tube sticking up is the return.The can is pressurized and the fuel will take the path of least resistance which will be the large hole at the bottom going to the carb until the needle and seat shut the fuel off and then the fuel will go back to the tank through the tiny .070 hole.No wild internal pump bypasses or anything else high tech.If the fuel is choosing to go to the tank its probably due to a restriction at the carb.

crackenzag

can't be restriction at the carb, or my fuel guage would read pressure. i teed in at the fuel line connection at the carb. if the carb or filter were restricted, it would still show pressure on the guage, would act as though the needle was closed on the guage. but I get 0. only until the return line is blocked off do I get fuel pressure at the carb and the car runs.

...Roger...

The check valve in the filter is towards the passenger side of the car-correct?

crackenzag

yea. the hole in the filter is facing out of the carb so the fuel can get in. the solid side of filter goes into the carb. im just wondering if the valve is making too much resistance or something, but even still i should show pressure on the guage.

...Roger...

It doesnt make sense the fuel is choosing the path of the smaller return hole unless there is blockage at the larger hole going to the carb.pics of your setup might help

...Roger...

One other thought to try if you feel like experimenting.Make a restrictor to put in the return line.Just drill a 1/16 hole in a plug and shove it in the return hose.This would take the place of the restriction in the pump if its missing.If this works then the pump was built wrong.Just a thought.

crackenzag

i tried the restrictor in the return line. I put a .070 carb jet in the rubber return hose with a hose clamp around it to hold it in place. it seemed to work for awhile, but then it went back to crap. I dont' know what happened, I haven't had a chance to look at it yet.

...Roger...

Have you tried removing the line at the carb attaching a rubber hose and putting that hose in a container and starting the engine?
tiasd

crackenzag

yea, i got like 1 oz in like 30 seconds of cranking. basically nothin... my GM pump should be here tomorrow. I HOPE it fixes it. I'm gettin upset at this thing.

...Roger...

No actually start the engine-the fuel in the bowl will run long enough to check.If you have no gas coming out of the line then your gauge,line or fitting at the pump must be more restrictive than the .070 restrictor you put in the return line.

crackenzag

well it's odd, cause the original pump i took off would produce 2-3 psi. enough to puts around in and idle and stuff, but when you get on it, and stay in it for a few seconds, it would run the bowl dry. but none the less, it would run. now with the new pump, it won't even run. I'm pretty sure it's the pump. my new dealer pump should be here today. we shall see....

...Roger...

So when you say with the new pump it wont even run.Does that mean at all or will only run with the return line pinched?

noonie

Just for fun
Remove the suction line from your pump, then hold your finger over the suction port while someone else cranks the engine over. You shoul feel a lot of suction on your finger.
If you don't get suction, remove the pump and manually operate it in a vise. Check to make sure you have the proper pump rod in there too. Check rod operation while someone cranks engine over. If someone overtightened a holding bolt for the pump rod at one time, it may be binding in the block.
You may want to blow compressd air back from the pump to the tank with the gas cap off while you have it apart.
Pretty simple system, can't be too big a mystery.

BTW, I like to run with 3# pressure and have no problems with starvation on a qjet.