Home » Public Forums » GMCnet » Holley fuel starvation?
| Holley fuel starvation? [message #307334] |
Sun, 18 September 2016 13:09  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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I'm having an issue with my fuel system. I've had an issue on and off over the years, but I've got it acting pretty repeatable right now.
The coach has a Holley 64-7259 carb. It's got an auxiliary electric fuel pump (just replaced - the old one was clearly bad), and new fuel filter (inline, and at the carb). It does still have the mechanical fuel pump.
The symptom - with the auxiliary fuel pump turned off, if I go full throttle for 10 seconds, the engine will start sputtering and missing. Flip on the aux. fuel pump, and a second or two later, I've got full power again.
It's doing this with the fuel tanks plenty cool (been inside the warehouse, with the inside temperature around 70). It's warm outside, but hard to imagine I'm getting vapor lock (or is it?).
I thought this problem had been due to the old aux. fuel pump, which was not running when powered up, and it took a LOT of pressure to even blow air through it. But clearly there's still something going on.
The aux. fuel pump I bought was the Mr. Gasket pump (the only thing I could come up with ASAP at the time). Is it possible that it's not doing a good job of passing gas when it's not powered?
http://www.autozone.com/fuel-systems/fuel-pump/mr-gasket-fuel-pump/732035_0_0/?checkfit=true
... or does anyone else have any good ideas about what might be wrong?
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Holley fuel starvation? [message #307337 is a reply to message #307334] |
Sun, 18 September 2016 14:06  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Thanks - I was looking for anything like that, but everything external to the carb looks good (fuel lines were all replaced with the proper ethanol-resistant lines a couple years ago). There aren't any kinks in any of the hard or soft lines.
I suppose there could be something gummed up in the carb float "circuit"... I'm thinking anything beyond that is no longer dependent on fuel pressure, but gravity feed from the float bowl.
One thing I did notice is that it took a fair amount of pressure to blow open the anti-siphon "valve" in the carb fuel filter (the Holley uses the same one that the Quadrajet uses). I'm tempted to reduce the spring tension on that to see if it helps. Heck, I suppose I could take it out altogether - after sitting for a few days, I always have to spin the motor a fair amount to get fuel to the carb anyway.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Holley fuel starvation? [message #307338 is a reply to message #307334] |
Sun, 18 September 2016 14:03 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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It's a good chance that it's the mechanical fuel pump.
Emery Stora
> On Sep 18, 2016, at 2:09 PM, Mark wrote:
>
> I'm having an issue with my fuel system. I've had an issue on and off over the years, but I've got it acting pretty repeatable right now.
>
> The coach has a Holley 64-7259 carb. It's got an auxiliary electric fuel pump (just replaced - the old one was clearly bad), and new fuel filter
> (inline, and at the carb). It does still have the mechanical fuel pump.
>
> The symptom - with the auxiliary fuel pump turned off, if I go full throttle for 10 seconds, the engine will start sputtering and missing. Flip on
> the aux. fuel pump, and a second or two later, I've got full power again.
>
> It's doing this with the fuel tanks plenty cool (been inside the warehouse, with the inside temperature around 70). It's warm outside, but hard to
> imagine I'm getting vapor lock (or is it?).
>
> I thought this problem had been due to the old aux. fuel pump, which was not running when powered up, and it took a LOT of pressure to even blow air
> through it. But clearly there's still something going on.
>
> The aux. fuel pump I bought was the Mr. Gasket pump (the only thing I could come up with ASAP at the time). Is it possible that it's not doing a good
> job of passing gas when it's not powered?
>
> http://www.autozone.com/fuel-systems/fuel-pump/mr-gasket-fuel-pump/732035_0_0/?checkfit=true
>
> ... or does anyone else have any good ideas about what might be wrong?
>
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
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| Re: [GMCnet] Holley fuel starvation? [message #307341 is a reply to message #307337] |
Sun, 18 September 2016 14:20 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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You might be having problem with the tank selector
Sent from my iPhone
> On Sep 18, 2016, at 12:06 PM, Mark wrote:
>
> Thanks - I was looking for anything like that, but everything external to the carb looks good (fuel lines were all replaced with the proper
> ethanol-resistant lines a couple years ago). There aren't any kinks in any of the hard or soft lines.
>
> I suppose there could be something gummed up in the carb float "circuit"... I'm thinking anything beyond that is no longer dependent on fuel pressure,
> but gravity feed from the float bowl.
>
> One thing I did notice is that it took a fair amount of pressure to blow open the anti-siphon "valve" in the carb fuel filter (the Holley uses the
> same one that the Quadrajet uses). I'm tempted to reduce the spring tension on that to see if it helps. Heck, I suppose I could take it out
> altogether - after sitting for a few days, I always have to spin the motor a fair amount to get fuel to the carb anyway.
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Holley fuel starvation? [message #307342 is a reply to message #307334] |
Sun, 18 September 2016 14:33 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Emery, that could certainly be the case. Just for giggles, I pulled the pre-filter off the carb, and it took a really good puff of air to blow the anti-siphon valve open... seemed excessive, given that the mechanical fuel pump should only be providing a few psi of pressure. I went ahead and cut off about four windings from the spring that holds it in place (a couple of the windings were "flat" so it wasn't a big adjustment). Re-testing the amount of pressure required to blow through the filter resulted in some - but not nearly as much pressure being required. Based on the readings I get when I blow into a fuel pressure gauge, I'd guess that it was taking 1.0-1.5psi to overcome the anti-siphon valve, and now it's somewhere less than 0.5psi.
I suppose even if the mechanical fuel pump is the issue, this may well "fix the problem" for now, at least until the mechanical pump deteriorates further. It's a little bit of a moot point since I do have the aux. fuel pump to fall back on, but I'm a belts and suspenders kind of guy. 
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Holley fuel starvation? [message #308087 is a reply to message #307334] |
Sat, 01 October 2016 14:57 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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Hi, all... So I took the coach from AZ to the CA coast (and back), after replacing the mechanical fuel pump. Gpt lots of walk-by comments and memories from other campers.
Clearly, the old mechanical fuel pump was bad, as the performance improved, and most noticeably, I don't have to crank the engine for 10 seconds any longer (fires right up).
But, I'm still experiencing a fuel starvation issue going up hills with the auxillary electric fuel pump off. The coach will cruise fine at 70mph or more on the flat without the aux. pump running (something it wouldn't do before changing the mechanical pump out). But if I climb a significant hill (or just put my foot on the floor for a while), it obviously runs out fuel and starts mis-firing. Flipping on the aux. pump will clear the problem in a couple seconds, and it pulls just fine from there.
Since I've replaced the aux. fuel pump (it was totally dead), the mechanical fuel pump (also bad), the fuel lines (with ethanol-rated lines, a couple years ago), and the fuel filters (inline and at the carb) (didn't see any problems with the filters, but it's cheap insurance).
I guess I'm down to troubleshooting that tank selector, like Jim K suggested... it sure seemed like I had a LOT of fuel flow when I pulled the line off the rear (input) of the aux. fuel pump though. I'm wondering if I might not just have a faulty bowl metering valve (or something like that) in the carb? Something that would limit fuel flow but that allows more fuel to flow when the fuel pressure jumps up a bit.
Any ideas?
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Holley fuel starvation? [message #308089 is a reply to message #308087] |
Sat, 01 October 2016 15:20 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Do you have a Quadra jet or a Holley carb? If you have a Holley, and you
have backfired back through the intake manifold, more than likely, you have
a bad power valve. Just a S.W.A.G. on my part. Fixed a number of them on
Holley carbs.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Oct 1, 2016 12:58 PM, "Mark" wrote:
> Hi, all... So I took the coach from AZ to the CA coast (and back), after
> replacing the mechanical fuel pump. Gpt lots of walk-by comments and
> memories from other campers.
>
> Clearly, the old mechanical fuel pump was bad, as the performance
> improved, and most noticeably, I don't have to crank the engine for 10
> seconds any
> longer (fires right up).
>
> But, I'm still experiencing a fuel starvation issue going up hills with
> the auxillary electric fuel pump off. The coach will cruise fine at 70mph
> or
> more on the flat without the aux. pump running (something it wouldn't do
> before changing the mechanical pump out). But if I climb a significant hill
> (or just put my foot on the floor for a while), it obviously runs out fuel
> and starts mis-firing. Flipping on the aux. pump will clear the problem in
> a couple seconds, and it pulls just fine from there.
>
> Since I've replaced the aux. fuel pump (it was totally dead), the
> mechanical fuel pump (also bad), the fuel lines (with ethanol-rated lines,
> a couple
> years ago), and the fuel filters (inline and at the carb) (didn't see any
> problems with the filters, but it's cheap insurance).
>
> I guess I'm down to troubleshooting that tank selector, like Jim K
> suggested... it sure seemed like I had a LOT of fuel flow when I pulled the
> line
> off the rear (input) of the aux. fuel pump though. I'm wondering if I
> might not just have a faulty bowl metering valve (or something like that) in
> the carb? Something that would limit fuel flow but that allows more fuel
> to flow when the fuel pressure jumps up a bit.
>
> Any ideas?
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Holley fuel starvation? [message #308097 is a reply to message #308089] |
Sat, 01 October 2016 16:42 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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James Hupy wrote on Sat, 01 October 2016 13:20Do you have a Quadra jet or a Holley carb? If you have a Holley, and you
have backfired back through the intake manifold, more than likely, you have
a bad power valve. Just a S.W.A.G. on my part. Fixed a number of them on
Holley carbs.
Jim Hupy
Jim, it's a Holley, and I did get some backfiring (happens when I go full throttle before the engine is warmed up). I'll check into that - it sounds like a perfect fit for my symptoms!
Thanks, Jim!
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Holley fuel starvation? [message #308098 is a reply to message #308093] |
Sat, 01 October 2016 16:44 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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hal kading wrote on Sat, 01 October 2016 14:11Mark,
If the mechanical pump draws through the electric auxiliary pump you may need a bypass with a check valve. Jim K. has them. I had the same problem on my 77 Kingsley. A by pass corrected it.
I thought about that, but I think others here have used the Mr. Gasket pump... maybe they also installed a check valve (don't recall seeing that though). I'll definitely look into that. I guess an easy check would be to just bypass the aux. pump with a piece of hose, and see if my problem goes away... Thanks!
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Holley fuel starvation? [message #308110 is a reply to message #307334] |
Sat, 01 October 2016 19:02 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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Just ordered a new Holley power valve - I took a wild guess and got one that opens at 4.5" of mercury vacuum - I figure that's about when I transition from "just past cruising along" to "need more power, now" mode. I certainly don't want it to open up when I'm just cruising along at 65-70mph. If I need to tweak it, they're dirt cheap (about $10 delivered) so it's no big deal.
I also added a kit to install a backfire check valve in the throttle body. Apparently Holley has built that into every carb since 1992 (IIRC) but mine was purchased in 1997 as a rebuilt, so I'm betting it doesn't have that feature.
A side note, the last couple times I started the coach (after installing the new mechanical fuel pump), it started VERY rich, pumping out black smoke for 10-15 seconds before settling down. I believe that I was getting pretty awful gas mileage on my trip last week, too, so my guess is that the bad mechanical pump was allowing the fuel to drain from the carb before it could drain into the intake through a ruptured power valve diaphragm. Or not... I should know for sure after Monday when I get the care package from Holley...
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Holley fuel starvation? [message #308117 is a reply to message #307334] |
Sat, 01 October 2016 20:02 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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The Mr Gasket pump(s) have built in check valves. Backfires will do dirt to Carter AFB carbs as well.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Holley fuel starvation? [message #308131 is a reply to message #307334] |
Sun, 02 October 2016 08:27 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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If you use two pumps, you have redundancy in case of a failure, and have the best protection against vapor lock, and eliminate the selector valve. The price is a relay, a fuseholder and wire, and a turnover switch.
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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