Fuel loading when hot

67HEAVEN · 04-30-06, 07:07 PM

Any ideas?

After driving until the engine is good and warm, if I leave it shut down for a half-hour or so, it seems to load up with fuel.

Holding the accelerator to the floor usually gets me going after a few cranks, but the smell of fuel and the puff of blue out of the sidepipes is nasty.

I've also noticed a more pronounced smell of gas in the garage after a cruise.

I've checked for leaks, and there appear to be none. Fuelie was over yesterday, and had a look at a few things (two heads better than one). Nothing obvious springs to mind. There's no purcolating down the butterflies after shutdown either.

The float levels are right too.

I found a temporary preventative cure, however. If I turn off the electric fuel pump about 30 seconds prior to shut down, the problem goes away at re-start. Since this pretty much empties the bowls, it would seem to suggest that the fuel is cooking in the bowls after shut down.

One more thing. Once the engine is good and warm, I occasionally get a notceable but very brief engine-stumble when turning a hard corner in either direction.

502 c.i. / Holley 850 with electric choke

Any ideas?

IH2LOSE · 04-30-06, 08:30 PM

Bob what pump do you have in the car and what is the psi?

Could be the pump is high pressure and the pressure pushes into the carb after setting a while.

As we all know high pressure has to go to low pressure even if the floats are satisfied and closed

67HEAVEN · 04-30-06, 09:03 PM

Larry,

It's the Holley #12-802-1 fuel pump:

Flows 110 GPH (free flow)
Flows 88 GPH at 9 PSI
Maximum pressure is 14 PSI

IH2LOSE · 04-30-06, 09:13 PM

Bob I thought on a standard carburated motor we were only supposed to run 6 to 8 psi

the simple answer is it sounds like heat soak/perculation

67HEAVEN · 04-30-06, 09:25 PM

Larry,

It came bundled with the Holley 12-803 Flow Regulator, in the same package.

http://www.holley.com/12-803.asp

67HEAVEN · 04-30-06, 09:57 PM

Quote:

Originally Posted by IH2LOSE

the simple answer is it sounds like heat soak/perculation

Yeah, it does. It got lots worse on the trip to Bowling Green last year. There was some excitement in the convoy, if I remember correctly.

Does anyone know where to source the aluminum heat shield (flat plate) that fits under the Holley carb? I had one years ago, but it grew legs.

Paranoid · 05-01-06, 04:20 AM

They show up on eBay occassionally. 3969835

gmjunkie · 05-01-06, 07:22 AM

Quote:

Originally Posted by 67HEAVEN

Any ideas?

After driving until the engine is good and warm, if I leave it shut down for a half-hour or so, it seems to load up with fuel.

Holding the accelerator to the floor usually gets me going after a few cranks, but the smell of fuel and the puff of blue out of the sidepipes is nasty.

I've also noticed a more pronounced smell of gas in the garage after a cruise.

I've checked for leaks, and there appear to be none. Fuelie was over yesterday, and had a look at a few things (two heads better than one). Nothing obvious springs to mind. There's no purcolating down the butterflies after shutdown either.

The float levels are right too.

I found a temporary preventative cure, however. If I turn off the electric fuel pump about 30 seconds prior to shut down, the problem goes away at re-start. Since this pretty much empties the bowls, it would seem to suggest that the fuel is cooking in the bowls after shut down.

One more thing. Once the engine is good and warm, I occasionally get a notceable but very brief engine-stumble when turning a hard corner in either direction.

502 c.i. / Holley 850 with electric choke

Any ideas?

67 have you thought about the Power valve in carb? It can only take 1 little backfire(usely more,but 1 is all it takes sometimes) to pop a small hole in diaphram, and that's all it takes for fuel run in through valve rubber membrane down the vacuum ports behind the metering block out of float bowl under throttle plates into intake!! You'll never see it LOOKING down through the Top!!

67, Did I ever tell ya how much I LOVE Holley's??

"Holley" Trusted by Auto Arsonist World Wide!!

gmjunkie · 05-01-06, 08:06 AM

Quote:

Originally Posted by Paranoid

They show up on eBay occassionally. 3969835

67 check with my son on E-bay 97s10ss4.3

He coughs up Old GM stuff all the time!! He's a BIG BLOCK BOY!! If it's not in his Items for sale,just e-mail him through E-Bay (He WILL get Back to Ya)!! Here's his 66 SS 396 Chevelle he's been Restoring for the Last 10 years!! Took him 6yr's to gather all the part's he wanted to Replace!! It will be finished this summer after Dad gets there to Blow the RED stain on it!! I don't know why he wants me to Stain it ,He's as good a Painter as I am!!

paul67 · 05-01-06, 08:07 AM

The heat shield can be ordered from your local speedshop or even the speciality catalogue at Canadian Tire.

I tend to agree with the 5-6psi for the fuel pump.

http://www.holley.com/108-70.asp

67HEAVEN · 05-01-06, 08:50 AM

Quote:

Originally Posted by paul67

The heat shield can be ordered from your local speedshop or even the speciality catalogue at Canadian Tire.

I tend to agree with the 5-6psi for the fuel pump.

http://www.holley.com/108-70.asp

Ahhhhh, thanks Paul. I'll get one of the Holley shields. As for the psi, the Flow Regulator is adjusted to 7psi, and I have an inline pressure gauge that confirms it.

I'd hesitate to drop it any lower, 'cause when I put my foot in it, it takes an oil-tanker to keep that monster satisfied.

67HEAVEN · 05-01-06, 08:52 AM

Quote:

Originally Posted by gmjunkie

67 have you thought about the Power valve in carb? It can only take 1 little backfire(usely more,but 1 is all it takes sometimes) to pop a small hole in diaphram, and that's all it takes for fuel run in through valve rubber membrane down the vacuum ports behind the metering block out of float bowl under throttle plates into intake!! You'll never see it LOOKING down through the Top!!

67, Did I ever tell ya how much I LOVE Holley's??

"Holley" Trusted by Auto Arsonist World Wide!!

Junk,

If cooling things down a bit doesn't solve it, I'll pull the Holley apart and check your theory.

Tom Bryant · 05-01-06, 08:58 AM

A couple of questions:

What is the pressure regulator set at? I bought the same one for my system and also bought a liqued filled pressure guage so I can actually see what the real pressure is at rpm. Mount it in line between the regulator and the carb. You should be able to get the same reading mounting it in the second outlet port of the regulator.

A follow up to that question would be do the fuel bowls continue to fill after the engine is shut down for awhile due to too high of residual fuel line pressure and drain down into the the intake ? I'm not that sharp on Holleys so I'm not sure this can even happen but if pressure causes fuel to continue to seep past the needle and seats as it sits it has to go someplace.

It seems like the Holley ads claim most new carbs have power valve blowout protection and that a device can be retrofit to carbs not having it. Does your carb have it?

I would add the heat shield. Also does your intake have exhaust gas crossover and is the passage blocked off to keep the intake cooler?

Tom

Summit 800115

motorman · 05-01-06, 09:15 AM

do you have the heat riser crossover in the intake blocked if not do it to remove the exhaust heat from the carb and intake manifold. even when gasoline was good back in the 60s i always blocked the crossover in any corvette i owned that had a aluminum intake to prevent the fuel from boiling in the bowls

67HEAVEN · 05-01-06, 09:23 AM

Quote:

Originally Posted by Tom Bryant

A couple of questions:

What is the pressure regulator set at? I bought the same one for my system and also bought a liqued filled pressure guage so I can actually see what the real pressure is at rpm. Mount it in line between the regulator and the carb. You should be able to get the same reading mounting it in the second outlet port of the regulator.

A follow up to that question would be do the fuel bowls continue to fill after the engine is shut down for awhile due to too high of residual fuel line pressure and drain down into the the intake ? I'm not that sharp on Holleys so I'm not sure this can even happen but if pressure causes fuel to continue to seep past the needle and seats as it sits it has to go someplace.

It seems like the Holley ads claim most new carbs have power valve blowout protection and that a device can be retrofit to carbs not having it. Does your carb have it?

I would add the heat shield. Also does your intake have exhaust gas crossover and is the passage blocked off to keep the intake cooler?

Tom

Summit 800115

Tom,

Yes, I have an oil-filled pressure gauge. The regulator is set for 7psi. I'll record the readings at various rpms. The 850cfm carb came with the 502, so it's a couple of years old.

The 502 intake does not have an exhaust gas crossover port.