1970 Trans Am Gas Consumption?

[Steve Wolfe]

Just getting my 70 TA back on the road after 30 years in storage and am astonished at how fast the fuel level drops in the tank.

The garage smells gassy after running it as well.

The carb is a Holley 650 double pumper and professionally rebuilt.

The fuel pump is about 40 years old, but the engine runs strong.

I have not found any leaks on the pump or anywhere else.

Also, the fuel level sending unit is new.

Any ideas are appreciated.

 

[bhill86]

Most likely running pig rich if you smell gas after running in the garage and not before.

 

[Pontiac Trans Am]

Do you know how to adjust your carb?

Thank you,
PTA Staff

 

[Steve Wolfe]

I have properly adjusted the idle circuit on the new carb.

After I drive it a little more I’ll check the plugs to see if it is running really rich as I suspect.

Can a mechanical fuel pump fail in a “supplying too much gas mode”?

Enough that it can force open the float needle valves at higher rpm?

Never heard of this but, I drove this car from the San Francisco area to Dallas in 1983 and don’t remember massive gas consumption.

 

[bhill86]

I believe it can do as you described.

I recently encountered someone with this exact issue, but I don’t recall where.

 

[79TURBO]

Just getting my 70 TA back on the road after 30 years in storage and am astonished at how fast the fuel level drops in the tank.

The garage smells gassy after running it as well.

The carb is a Holley 650 double pumper and professionally rebuilt.

The fuel pump is about 40 years old, but the engine runs strong.

I have not found any leaks on the pump or anywhere else.

Also, the fuel level sending unit is new.

Any ideas are appreciated.

When I picked up my project car, I could not get the darn thing running after many weeks of troubleshooting.

Found that old gas had settled, dried up, and caused serious rust problems inside the tank.

My troubleshooting method was to come home one day and see the TA will fuel leaking down the driveway, LOL.

It had finally rusted through in one spot.

The fuel problem was solved after replacing the tank, sending the unit, and rebuilding the carb.

I hope your issue turns out to be much simpler.

 

[Steve Wolfe]

Just getting my 70 TA back on the road after 30 years in storage and am astonished at how fast the fuel level drops in the tank.

The garage smells gassy after running it as well.

The carb is a Holley 650 double pumper and professionally rebuilt.

The fuel pump is about 40 years old, but the engine runs strong.

I have not found any leaks on the pump or anywhere else.

Also, the fuel level sending unit is new.

Any ideas are appreciated.

Thank you, sir!

I have a new fuel pump on order, so I will try that next because the existing one is so old.

I expect the sending unit I received from xxxx may not be correct Or defective in its calibration.

I’m going to have to figure out some troubleshooting plan.

 

[TOG]

Does your carb have sight plugs in the bowls?

If so, open them up after placing some rags underneath the ports to catch any fuel that spills out. Start the car and observe the fuel level in the bowls.

It should be at about the level of the lowest point of the viewport (this is where an electric fuel pump is very helpful, just switch it on without running the engine).

If fuel comes pouring out of one or more viewports, the floats are misadjusted, stuck, or the fuel pressure is too high, but that seems unlikely with a stock mechanical fuel pump.

 

[Steve Wolfe]

Thank you sir! Have a new fuel pump on order so I will try that next just because the existing one is so old. I expect the sending unit I received from xxxx may not be correct Or defective in its calibration. I’m going to have to figure out some kind of troubleshooting plan.

Installed new carter deep canister fuel pump that matches the old one in appearance.

I started the car, and fuel erupted from both bowl vents on the Holley 650.

Did not do this with the old pump.

I have not been able to determine exactly which pump this car came with and if it is compatible with a Holley.

Firebird central lists a deep canister pump for 1970 but says it is discontinued.

Very frustrated at this point.

 

[Steve Wolfe]

Does your carb have sight plugs in the bowls?

If so, open them up after placing some rags underneath the ports to catch any fuel that spills out. Start the car and observe the fuel level in the bowls.

It should be at about the level of the lowest point of the viewport (this is where an electric fuel pump is very helpful, just switch it on without running the engine).

If fuel comes pouring out of one or more viewports, the floats are misadjusted, stuck, or the fuel pressure is too high, but that seems unlikely with a stock mechanical fuel pump.

No sight plugs on my holley 650.

 

[TOG]

I don't know the exact Carter pump you have, but the one shown on the Carter website for your application, Part # M6112, shows a spec pressure of 6.5 PSI.

This is a tad on the high side for a Holly; 5 PSI or so might be more like it.

Has the carb ever worked correctly since it was rebuilt?

Could the floats have never been adjusted since the rebuild?

Mechanical Fuel Pump

carterengineered.com

 

[Steve Wolfe]

I don't know the exact Carter pump you have, but the one shown on the Carter website for your application, Part # M6112, shows a spec pressure of 6.5 PSI.

This is a tad on the high side for a Holly; 5 PSI or so might be more like it.

Has the carb ever worked correctly since it was rebuilt?

Could the floats have never been adjusted since the rebuild?

Mechanical Fuel Pump

carterengineered.com

The carb seemed to work fine with the previous fuel pump other than using a ton of fuel per the gas gauge.

Thats the core problem I am trying to correct.

My car has a return line from the fuel pump to the tank on it.

M6112 doesn’t appear to support that.

This new carb has not been apart since I received it from Allstate Carbs.

This car used to run great with decent gas mpg back in the mid/late 80’s with the previous Holley 650 and previous fuel pump.

Thanks for the info above; I’ll check out that link.

 

[Steve Wolfe]

The carb seemed to work fine with the previous fuel pump other than using a ton of fuel per the gas gauge.

Thats the core problem I am trying to correct.

My car has a return line from the fuel pump to the tank on it.

M6112 doesn’t appear to support that.

This new carb has not been apart since I received it from Allstate Carbs.

This car used to run great with decent gas mpg back in the mid/late 80’s with the previous Holley 650 and previous fuel pump.

Thanks for the info above; I’ll check out that link.

I looked at the picture again, and M6112 does have a return line, but my fuel line won’t fit the bottom vertical inlet.

 

[TOG]

Looked at the picture again and M6112 does have a return line but my fuel line won’t fit the bottom vertical inlet.

Possibly the float bowls were never adjusted after the carb was rebuilt.

 

[Steve Wolfe]

Possibly the float bowls were never adjusted after the carb was rebuilt.

I will check them today, thanks!

 

[Steve Wolfe]

I will check them today, thanks!

Found primary float filled with gas.

New floats are in the mail.

Will check the fuel pressure and install new floats when they arrive.

 

[TOG]

That would do it.

Not the first time that has happened.

Glad you found it!

 

[Steve Wolfe]

New carb floats were installed, and the primary bowl is no longer flooding the vent.

Engine purred at idle and ran very strong under WOT.

Gas consumption still seems very high based on the fuel gauge.

After parking it, I took off the gas cap, and there was a little pressure in the tank.

I will check the main vent line from the tank to the vapor canister for obstruction.

I may also have to take out the new tank-sending unit and check its cal.

 

[Steve Wolfe]

I removed fuel tank and vent box above the diff.

The vent line up front to the vapor canister is an orifice now clean.

I took out sending unit, and the suction filter had fallen off, and there was a small amount of fluid in the plastic float.

It read ~0 ohms empty and ~95 ohms full.

Not sure if this is compatible with the gauge or not.

The tank has about 2.5 inches of fuel in it, and the tank is 6 inches deep.

This should equate to ~42%, yet the gauge was reading slightly above 1/8 full.

The sending unit is a Spectre, I believe.

Can anyone recommend a better (compatible) sending unit?

 

[BillyMagg]

I removed fuel tank and vent box above the diff.

The vent line up front to the vapor canister is an orifice now clean.

I took out sending unit, and the suction filter had fallen off, and there was a small amount of fluid in the plastic float.

It read ~0 ohms empty and ~95 ohms full.

Not sure if this is compatible with the gauge or not.

The tank has about 2.5 inches of fuel in it, and the tank is 6 inches deep.

This should equate to ~42%, yet the gauge was reading slightly above 1/8 full.

The sending unit is a Spectre, I believe.

Can anyone recommend a better (compatible) sending unit?

I would suggest you measure the actual fuel consumption, by filling your tank, noting the milage, driving the car until it is indicating a 1/2 tank or so, then taking it an filling it back up to the filler neck... then divide the miles traveled by the fuel used?? very simple,, then you will have a number... Next, the 650 double pumper has never been known to offer lower fuel consumption.. the double accelerator pumps are designed to "flow more fuel".. a good Quadrajet might be a place to start? or the Holley "Spread Bore"?