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Discussion Starter · #1 ·
Have a 66 GTO with a 1972 455. Just took it out for the first time this year. Stored it in November. Full tank of gas, fuel stabilizer. Ran fine today until I kicked in the secondary’s. It then started bucking and seemed to want to stall until I backed off. Pulled down a side street when all of a sudden it completely stalled. Tried starting it for about 5 minutes, cranked fine but would not catch. Finally like nothing was wrong it started. I drove about a mile when it stalled out again. This time it restarted in about a minute. Drove home about 3 miles and no problem. I let it run at the house for about 15 minutes without any issue. Any ideas why it would act up when secondary’s kicked in, then stall. It ran fine last year. Put in a new fuel filter last year. Thanks in advance for any help.
 

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Hello
this issue will bring alot of suggestions ....
but
if it were my car ,,,,
and it happened to me my thoughts would go like this
ok I just rompped on it and it didnt like that.... so my thoughts go to carbueration
what carb are you running ? q j et part number ??? or ?
if its the 72 q jet still I am thinking carb issue,,,
glad you got home ,,,, so I am home now and its idling fairly good correct ?
I would go to the tail pipes and listen closely
I would stick a finger in the tip and observe the black or grey residue
does it smell gassy when running ???
1st when I got home I would have popped the hood and looked for fuel or smelled for it ,,,
then let it run ,,,
I would pull a plug or 2 and check color ,,,
leanin towards the carb ....
did it smell gassy when it fired up ??
are you running points in the distributor,,,,

go slow,,,, start simple .... like a drive without throttling it,,, gain confidence,,,b4 throwing $$ at it
the choke could be acting up ,,,
if the plugs are brown its a lean condition
if the plugs are black too much fuel or weak spark issue

just my .02 ,,,, if it were me..............
sounds like the 4bbl flappers were stayin open and it flooded ,,,, but .... plug check
 

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Discussion Starter · #3 ·
Hello
this issue will bring alot of suggestions ....
but
if it were my car ,,,,
and it happened to me my thoughts would go like this
ok I just rompped on it and it didnt like that.... so my thoughts go to carbueration
what carb are you running ? q j et part number ??? or ?
if its the 72 q jet still I am thinking carb issue,,,
glad you got home ,,,, so I am home now and its idling fairly good correct ?
I would go to the tail pipes and listen closely
I would stick a finger in the tip and observe the black or grey residue
does it smell gassy when running ???
1st when I got home I would have popped the hood and looked for fuel or smelled for it ,,,
then let it run ,,,
I would pull a plug or 2 and check color ,,,
leanin towards the carb ....
did it smell gassy when it fired up ??
are you running points in the distributor,,,,

go slow,,,, start simple .... like a drive without throttling it,,, gain confidence,,,b4 throwing $$ at it
the choke could be acting up ,,,
if the plugs are brown its a lean condition
if the plugs are black too much fuel or weak spark issue

just my .02 ,,,, if it were me..............
sounds like the 4bbl flappers were stayin open and it flooded ,,,, but .... plug check
 

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Discussion Starter · #4 ·
It’s a q jet 7042264. When I got home I popped the hood and pulled the air cleaner..... no smell or sight of raw fuel. The choke plate was wide open. I did go back to the pipes to just view for black smoke ( running rich) but did not observe anything. I didn’t finger the pipe as you suggested. I will run it and do that as well as pull out a plug.
what’s odd is that simply shut down after I had drove down a side street at about 35 mph. Then once I had it running I stayed at about that speed when it stopped running again. Never detected a raw fuel smell.
I bought the car a year ago, so I’m not sure if the tank or lines were ever replaced. Had filter replaced in carb, but also observed that the car had a small canister type filter right off the tank, that had a date mark of 2 years ago. The ignition is HEI.
 

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no back fires ??? back fires in the carb is usually a lean condition .. exhaust is unburnt fuel

vapor lock .. hmm yah good idea
non vented correct gas cap and a clear vent tube by the trunk latch ,,,, you may pull the tube and blow air thru it

fuel filter in back leads me to believe some one else was having a dirty tank issue,,,
you may look closer and see if the tank strap bolts have been removed or the tank strap s may not be back on in the old
position ,,, maybe some ones been in there ...

good eye on finding the filter,,,, I would pull it and open it up ,,,

it could very well be fuel starving ,,,,dirty sender sock ... etc
 

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Discussion Starter · #7 ·
So the vent tube is near the trunk latch? I don’t recall seeing it, but then I never actually looked for it. Vapor lock seems logical, but I never had that issue last year. But, the line from the fuel pump to the carb is within 1/2” of top radiator hose and thermostat.
 

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Agree with black judge and Jedi, likely fuel issue and you can’t rule out vapor lock.

I think that your full take of “November gas” is winter blend gas. Winter blend gas has very different vaporization numbers than summer blend gas. This is so in cold temps the gasoline will vaporize rapidly and fire off.

Vapor lock gives very similar symptoms, stall and restarts after sitting. What happens is a vacumn is created by the fuel pump to suck the fuel thru, but vacumn “lowers” the vaporization rate even more, and you already have winter blend gas! So it gets really low, vaporizes in the fuel line, and guess what,...vapors don’t pump, liquid pumps and now you demand liquid for the increased throttle and secondaries and it ain’t there. The secondary’s open and instaed of fuel and air you get a big gulp of AIR, which causes a lean stall.

yes it laters idles for 15 minutes but the fuel pump is then not under high RPM load causing a higher vacumn and lowering the boiling point of the fuel. Fuel stabilizers don’t have any effect on vaporization rate, they prevent phase separation where water from condensation and fuel separate. You need the stabilizer but it saves you from another problem, not this one.

firstI would get that tank filled with fresh summer blend gasoline. and add a bottle of Redline S1 Complete fuel system cleaner to that full tank. To help clean out anything at all that may be in there.

Now it could be anything in the list that black judge said, he is leading you right, and they sho7ld all be checked. This is just one possibility. It could also be electrical or even an oil covered inside distributor. I would recommend that you pull the distributor cap and look inside, make sure it is not soaked in oil. When that happens it has similar symptoms.

But I would begin with fresh fuel and Redline as the first step in your investigation. Also the fix for vapor lock generally is a fuel return line to the tank.

Good luck, let us know how you do!
 

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Discussion Starter · #10 ·
Thanks for everyone’s help. I greatly appreciate it! Lucky me with a full tank of winter blend gas.
 

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Discussion Starter · #11 ·
no back fires ??? back fires in the carb is usually a lean condition .. exhaust is unburnt fuel

vapor lock .. hmm yah good idea
non vented correct gas cap and a clear vent tube by the trunk latch ,,,, you may pull the tube and blow air thru it

fuel filter in back leads me to believe some one else was having a dirty tank issue,,,
you may look closer and see if the tank strap bolts have been removed or the tank strap s may not be back on in the old
position ,,, maybe some ones been in there ...

good eye on finding the filter,,,, I would pull it and open it up ,,,

it could very well be fuel starving ,,,,dirty sender sock ... etc
Thanks for everyone’s help. I greatly appreciate it! Lucky me with a full tank of winter blend gas.
 

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Discussion Starter · #12 ·
After reading a lot of material about ethanol gas blends and having the winter blend gas still full in the tank, I think my first step will be to get most of it out of the tank. Appears that the water in the gas sinks to the bottom so that’s most likely what I’m experiencing. Plus with that odd placement of a filter right off the tank, I’m sure the previous owner had something going on.
I think all the fuel tank and lines maybe original so I’m considering replacing all of it. Also purchased a Heatshield Thermaflect sleeve to run from the carb to the fuel pump, just in case I’m getting vapor lock from that area.
 

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Good moves do you have a fuel return line? From the fuel pump or near carb to the tank, that is the fix for vapor lock. The Pontiac engineers put them on AC cars back in the day because of course they run hotter from condenser dumping heat in front of the radiator.

If you are replacing fuel lines you can this easily. You need a fuel sender in the tank that has a return line, and a fuel pump that has a return line. That keeps a small amount of fuel always moving in the system so you don’t get vapor lock. All heat shielding is good, you can have too much.
 

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I Meant to say you CAN’T have too much heat shielding. Fuel return lines are great and keep fuel cool, so that is a good move as well. Just getting some summer blend gasoline will help as the vaporization temperatures are higher.
 

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What that filter does is it makes the pump work harder to pull the gas through and creates a vacumn. A vacumn of course is the absence of pressure and therefore lowers the vaporization point of fuel.

It works like your radiator cap, by adding 16 lbs of pressure on the coolant system from the cap the boiling of the water is raised to maybe 240 degrees or more. Now when you pull the vacumn you work the physics in the opposite direction. You reduce pressure and lower that point. Add together the winter blend gas, no fuel return line and a fuel filter that adds a restriction at the very end of that long fuel line...and voila! A perfect recipe for create a vacumn and vapor lock.

Heat soak is different that is when the vehicle is shut off and all the temps begin to soak together and equalize. That is what then boils the gas in your carb and fuel lines.

this stuff is all fixable you just have to do what you are doing and take it head on.
 

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Oh and good move to put heat shield from pump to carb, that works against heat soak, and that is a very hot area. But vapor lock occurs on the suction side of the pump, from the pump to the tank, because that is where the vacumn is created, and where the vaporization rate is lowered and the vapor forms.....and you can’t pump vapor.
 

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What that filter does is it makes the pump work harder to pull the gas through and creates a vacumn. A vacumn of course is the absence of pressure and therefore lowers the vaporization point of fuel.

It works like your radiator cap, by adding 16 lbs of pressure on the coolant system from the cap the boiling of the water is raised to maybe 240 degrees or more. Now when you pull the vacumn you work the physics in the opposite direction. You reduce pressure and lower that point. Add together the winter blend gas, no fuel return line and a fuel filter that adds a restriction at the very end of that long fuel line...and voila! A perfect recipe for create a vacumn and vapor lock.

Heat soak is different that is when the vehicle is shut off and all the temps begin to soak together and equalize. That is what then boils the gas in your carb and fuel lines.

this stuff is all fixable you just have to do what you are doing and take it head on.
Filters at the back where the gas tank is is typically done when using an electric "pusher" fuel pump. Is there an electric fuel pump you are not seeing or does it look like one may have been used and removed?

Depending on the type of fuel filter material/brand, some can be removed, flushed out, and reused.
 

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Discussion Starter · #19 ·
The gas has been in the tank since November, so it’s definitely winter blend with ethanol. The fuel filter coming off the tank appears to be the Delco style that would possibly go between the fuel pump and carb. No electric fuel pump on the car.
I plan to start with the most obvious and get all that old gas out of the tank. Then add fresh fuel and Redline fuel cleaner. I will insulate/wrap the fuel line from the pump to the carb.
Hopefully this will solve the problem once that fresh fuel is in the system, as it’s run fine until this last week. I think it might be original tank and lines. I plan on getting those replaced no matter what. And run that additional line from the fuel pump to the tank.
 

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I had same problem, my electric fuel pump wasn't keeping up with the hard aacceleration.Idle was fine. My fuel pressure gauge dropped from the usual 5 lbs to 3.5. Replaced pump and filter, no issues. Install a fuel pressure gauge, I bet your filter is causing restriction. Remove and place a new filter between pump and carb. I bet your problem will be resolved. A pressure gauge at the carb will alert you to any issues.
 
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