# Fuel Supply or Carb Issue



## jtwoods4 (Dec 22, 2011)

1969 GTO, 472 Stroker, Holly 850.

I have a fuel bug to figure out. Sometimes when driving the engine will start sputtering and I have to feather the throttle to get the fuel flowing again. Sometimes the engine will literally die while driving and I have to coast and pop the clutch to get it started again. It definately behaves like the fuel supply is getting blocked by something. I noticed the problem happens most when I get on the thottle really hard, then when I change gears and the RPMs drop during the shift the emgime fails to get adequate fuel when accelerating into the next gear. Where should I start trouble shooting? 

JW


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## BearGFR (Aug 25, 2008)

The 'under acceleration' problem to me sounds like a classic insufficient fuel supply problem. Perhaps the pump is going away, or the fuel line just isn't big enough, or it could be some sort of blockage (like a clogged filter).

What kind of pump? How big is the fuel line from the tank to the carb?

Bear


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## Rukee (Feb 8, 2007)

Non vented cap when there should be a vented one? Remove or loosen the gas cap to test.


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## jtwoods4 (Dec 22, 2011)

I am not sure what brand of pump or filter but I will find out and post the details. Looks like a cheap filter. Problem may be is that the filter can't handle the fuel supply needed for the performance engine. I will also check the size of the fuel lines. I know the fuel tank may be the original because the bolts holding it in are extremely rusted and corroded. It may be easier to just replace each component from smallest to largest until the problem goes away.


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## jtwoods4 (Dec 22, 2011)

Rukee I just flipped through your 65 GTO slideshow pictures. That is such a beautiful car.


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## Rukee (Feb 8, 2007)

jtwoods4 said:


> Rukee I just flipped through your 65 GTO slideshow pictures. That is such a beautiful car.


Thanks man! :cheers

....a `69 would be my next favorite year.


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## geeteeohguy (Feb 2, 2008)

I think the very first thing I would check is the gas cap vent. It's fast, easy, and free.


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## jtwoods4 (Dec 22, 2011)

I just found the vent tube located a few inches from the gas cap. I disconnected the tube and blew through it to make sure it was clear of any debree. Air flows through the tube fine so I assume the tank is venting correctly.


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## jtwoods4 (Dec 22, 2011)

BearGFR said:


> The 'under acceleration' problem to me sounds like a classic insufficient fuel supply problem. Perhaps the pump is going away, or the fuel line just isn't big enough, or it could be some sort of blockage (like a clogged filter).
> 
> What kind of pump? How big is the fuel line from the tank to the carb?
> 
> Bear


The fuel line size is the stock size. The car has the stock fuel lines to and from the tank.


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## Thumpin455 (Feb 17, 2010)

Ok you have a 472 with an 850 Holley right? You have a stock mechanical pump, or an electric one? The old 455 in my 70 and the 455 in the Formula would both run out of gas either at the top of first or just after hitting second gear. The stock pump couldnt pull enough fuel from the tank to feed the engine. My fix was a Carter electric pump, and it fed the 540hp 455 that was in the Bird. I mounted the pump back by the tank, as close to the pickup as possible. Since it happens most when you are hard into it, that would be my guess.


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## jtwoods4 (Dec 22, 2011)

I have the stock mechanical pump and stock fuel lines.


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## jtwoods4 (Dec 22, 2011)

I am considering making the following upgrades to my fuel system. Not sure if I need adapter to connect to fuel lines to the pump, filter, and carb

1. 1/2 inch fuel line to filter, 1/2 inch fuel line to pump, 1/2 fuel line to carb

2. Robb Mc Fuel Pickup – 1/2" Sending Unit, PN 1069
RobbMc Performance Products - 1/2" Sending Unit

3. Robb Mc 100 Micron pre pump fuel filter. Flows 400 GPH. 1/2 NPT ports 
RobbMc Performance Products - Fuel Filters

4. Robb Mc 550 HP Mechanical Fuel Pump WITH 5/16 mounting holes. WITHOUT VAPOR RETURN LINES. I will user an air filter on the second pickup line and use it for vent purposes
RobbMc Performance Products - Pontiac 550HP Fuel Pump


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## BearGFR (Aug 25, 2008)

I've got all RobbMC stuff, and it's high quality. He's really good at standing behind his parts too.

Bear


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## jtwoods4 (Dec 22, 2011)

UPDATE...

I replaced the stock fuel filter with a high flowing filter. Problem solved. Runs smooth with no sputtering.

Here is the filter I installed.
http://www.summitracing.com/parts/EAR-230206ERL/


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