holley carb trouble, help

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Aug 20, 2003 | 04:12 PM

JRODDVETTE

Thread Starter

Racer

Joined: Oct 2002

Posts: 396

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From: Coventry CT

holley carb trouble, help

i have a 79 vette with a holley 700cfm dual feed, double pumper carb.
the problem i am having is after i drive it for a while(it is fully warmed up) the carb. over flows and the engine shuts off. i have a aeromotive fuel system in the car so it keeps pumping fuel all over the engine until i shut the ignition off.
i have removed both fuel bowls and inspected for dirt(none found), replaced both needle & seats with holley parts, made sure the floats are not dragging on the inside of the bowl or binding anywhere, i removed the floats to see if they may have filled up with fuel(they didn't) i set my floats to the correct level(just below the sight plug) i also have a fuel pressure gauge mounted under my hood cowl that i can see at all times(set at 6 1/2 psi.)
and i replaced the inline fuel filter.

i have -10 fuel lines that run to my fuel pressure regulator, and they run semi close to the headers and heater hoses. will heat cause a problem like this?
i have two different holley tuning books, and have completed all of the trouble shooting instructions but the problem still exists.

if you have any suggestions please reply.

[Modified by JRODDVETTE, 4:21 PM 8/20/2003]

Aug 20, 2003 | 04:17 PM

BB wowbagger

Melting Slicks

Joined: Feb 2002

Posts: 2,298

Likes: 1

From: Sodertalje/Sweden

Re: holley carb trouble, help (JRODDVETTE)

Could be the fuel boiling in the carb.Try with a spacer inbetween the carb and intake. :thumbs: :cheers:

Aug 20, 2003 | 04:19 PM

Fevre

Race Director

Joined: Mar 2001

Posts: 11,322

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From: Living in the Hartland

Re: holley carb trouble, help (JRODDVETTE)

Is the bowl overflowing or is it coming out the vent tube? Might have a plugged passege somewhere. I had a plugged idle passege and it would overflow out the vent tube. It took me a while to figure it out, one clue is your idle screws do little when adj, and I tore the carb apart then used some comp air to blow it out. Put it back together and the problem stopped.

Aug 20, 2003 | 04:26 PM

JRODDVETTE

Thread Starter

Racer

Joined: Oct 2002

Posts: 396

Likes: 1

From: Coventry CT

Re: holley carb trouble, help (Fevre)

it's coming out the vent tube, filling the carb up then over flowing through the air cleaner onto the intake.

how do i check for the clogged idle passage?
thanks for the help

if it boils the fuel would it cause it to overflow?

Aug 20, 2003 | 04:32 PM

Fevre

Race Director

Joined: Mar 2001

Posts: 11,322

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From: Living in the Hartland

Re: holley carb trouble, help (JRODDVETTE)

One way to see if it a float level problems is to adj the floats low enough to allow you to idle and not spill out the site hole then let it idle and see if it starts to come out. Boil over could also be a problem with the higher pressure being regulated down to 6 1/2 psi. I have seen where people will use a pressure reg and then use one of the out ports as a return to allow less pressure build up between the pump and regulator. How hot does the reg get? Think I took the carb apart and used a length vac hose to mouth blow into each passege to see if it was blocked then blew it out with compressed air.

Aug 20, 2003 | 04:41 PM

Brettmc

Safety Car

Joined: Jul 2002

Posts: 3,770

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From: St Louis MO

Re: holley carb trouble, help (JRODDVETTE)

If you've got fuel coming out the vent tube, the bowl is filling up past the float level. This means your fuel system has excessive pressure, blowing gas past the needle and seat. I would look at the venting in your fuel system. Try loosening the gas cap and driving around. I don't know if fuel getting hot in the lines next to headers would cause this but you could try wrappin them with some sort of insulation. Try venting the system by loosening the gas cap first.

Brett :thumbs:

Aug 20, 2003 | 04:42 PM

JRODDVETTE

Thread Starter

Racer

Joined: Oct 2002

Posts: 396

Likes: 1

From: Coventry CT

Re: holley carb trouble, help (Fevre)

i do have a -8 return line back to the gas tank, so i don't think it's pressure build up. but i WILL try loosening the gas cap.

the thing is, after it overflows i un-plug the fuel pump relay and crank the motor over to empty the cylinders of raw fuel. then i plug it back in and i start the engine and i can drive it home(i've driven about 3 miles) and it didn't do it again.

i will take your advice and check for clogged passages. but if you or anyone else has any other suggestions, i'm willing to try anything.
thanks again

[Modified by JRODDVETTE, 4:58 PM 8/20/2003]

Aug 20, 2003 | 04:52 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,373

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From: At my Bar drinking and wrenching in Lafayette Colorado

Re: holley carb trouble, help (JRODDVETTE)

JROD -
Unrelated to your fuel overflow problem, but you might want to install a Holley oil pressure switch so your fuel pump shuts off when the engine dies. We run them on all of our electric pump motors out here to keep the cars from burning to the ground in the event of a backfire or accident...

Yes, fuel boiling in the bowl can cause fuel to blow out the vent stack and to discharge out the main discharge nozzles. The symptoms of this will be the fuel bubbling and percolating up through the vent. If, on the other hand, you have a geyser shooting out the vent, you have a needle/seat that is failing to shut off the fuel flow due to either excessive pressure or a defective needle seat/float system. If this is the case, the geyser should stop when you shut off the pump; boiling fuel will continue to bubble out the vent even after pump shutdown.