carb issues

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Dec 9, 2009 | 10:18 PM

OldSkewl 79

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From: Sainte Genevieve, Mo

carb issues

Hello all.. so far you have been great help!! But I ran into another problem.
Holley 600 vac secondaries is the topic. Mechanical fuel pump.
Idles fine. Speeds up to 45mph fine. At highway speeds 60-70mph it sputters after about 1 mile and acts as if running out of fuel. I cleaned out carb, filters and lines. Nothing too bad. Hell its a 30 year old truck LOL..
Ok well I take it out down same road.. almost in the same spot it sputters the same way.. I brought the truck home and installed a Holley Blue pump inline before the tank. The mechanical fuel pump is still attached and in line. I ran down the same stretch of road and it started to die.. I flipped the switch in 3 seconds it was running great. Left it on for another 10sec and I can continue down the road for another mile... then it happens all over..
My assumption is that Im running out of fuel.. be it a weak mechanical pump or ???

What else can be causing this.
Thanks
C

Dec 9, 2009 | 11:44 PM

Beanscoot

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Joined: May 2007

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From: British Columbia

Perhaps your gas cap is not venting so as gas is removed from tank air cannot go in to replace it. Try running with the cap off or loose next time to see if it still happens.

Dec 10, 2009 | 12:23 AM

Sand_Man

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From: Rogue River, Oregon

If I had to venture a guess, I'd say you're right on about it running out of gas. My first thought would be the mechanical fuel pump may have a hole in the diaphram. Anything coming out of the weep hole? Running an electric pump in series with a mechanical pump is not the way I would do it, mostly because there's no good reason to. A mechanical pump should provide all the pressure and volume any street small block can use. If the mechanical pump is ok, then the next area of suspicion should be the float level. If you have adjustable floats, make sure they're adjusted correctly, either with the screw adjustment or by bending the tang on non-adjustable ones. But I'd check the pump's pressure first. Hope this helps, Jim

Dec 10, 2009 | 09:03 PM

OldSkewl 79

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From: Sainte Genevieve, Mo

Cap is typical for a 79 stepside.. LOL.. barely hangs on.. I checked it tonight as I walked up driveway I bumped it and it moved around.. not tight but not falling off yet.. Im sure if this was an off road truck it would fall right off..

Where is the weep hole located? When the truck is idleing and throttleing my gauge reads 5 psi.. Gauge is a cheapie though. I will try to get a better more accurate gauge.

The electric pump was just a last ditch effort to see what was up.. as everyone $$$ are limited. I will check float levels tomorrow night after work.
I have another question. WHen running at idle to say 45 am I just pulling fuel from the front bowl? Then same question about 45+ but is it comming from the rear bowl when only the secondaries are open?

Thanks
C

Dec 10, 2009 | 09:09 PM

Sand_Man

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From: Rogue River, Oregon

If you look at the mechanical pump, it should be dry. If it smells of gas and is wet with gas, there's a hole in it to let you know that the pump's diaphram has a hole in it and the pump is about to quit. 5 lbs is enough if it has that much pressure at highway speeds. Also, lots of Holley carbs have a sintered bronze filter located right where the fuel inlet is. You need to remove the line from the bowl to see if yours does. If so, I'd take it out and at least clean it. Lots of guys simply remove them altogether. They really aren't necessary if you already have a filter elsewhere in the system.

Dec 11, 2009 | 09:35 PM

OldSkewl 79

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From: Sainte Genevieve, Mo

Well I feel really dumb... I went and got a regulator for the line.. set is up at 8psi for the holley... Ran down the road and same issue happened... then I hit the ol electric pump and ran the truck a bit.. PRoblem solved.. WhOohoo... came home and decided to double check my regulator settings.. I had the pump turned off and was going to disconect the mechanical pump.. I looked down to see the clear filter and its was surging and was only 1/4 full.. I was confident that I found my culprit.. then I noticed the fuel line running from the fuel pump to the hard line... I had just replaced it.. it was kinked like a garden hose and collapsed ... god I cant believe this.. I shortened the hose and let it go until tomorrow. I have a 60 mile run on the interstate one way..
I know this is the problem.. there was no fuel leaking from the weep hole or anywhere.

Let you all know more later..
Thanks
C