Starved For Fuel?

[Thomas]

It finally stopped raining long enough for me to take my '69 Camaro for a drive on Saturday.
I had installed a new Flowmaster exhaust a few weeks ago and had yet to hear what it sounded like on the hiway and to feel whether it improved my performance.

I came across a problem the first time I "got on it". It appears the carb is starved for fuel.

It pulls all the way through first gear, but part way through second it looses power and has even backfired through the carb.
Once I get off the gas, the car just performs flawlessly.

If I drive the car "normally" it has no drivability issues and shows no other symptoms.
It starts every time and idles flawlessly.

The car has been in heated storage from late 2006 until late May of this year.
I did start it on a regular basis every month or so when it was in storage.

I have had the car on 3 long drives since June with no other issues.

The fuel pump was replaced in 2000 with an AC Delco unit and I have only put 5000 miles on the car since then.

I have not yet checked the float levels and will probably do that tonight, but I am thinking not enough volume through the pump.

The engine is basically a stock L72 (427 block with all the other pieces from the original L78) with headers.

Am I on the right track?

[Chevy454]

Unless there's something mechanicly wrong with the pump, it should be plenty...checking the floats would be a good idea...your secondaries working correctly? What power valve in the rear? My gut thinks a weak pump would show up farther down-track than in 2nd, but I'm sure Eric will correct me...

I tried a high flow pump from Carter a couple years ago in place of our stock AC...the A-B-A testing showed absolutely *no change* when swapping pumps...I may be jinxing myself here, but our 3700+ pound Camaro will trap anywhere from 117-118mph on our *non-sexy" stock pump.

[Thomas]

[ QUOTE ]
Unless there's something mechanicly wrong with the pump, it should be plenty...checking the floats would be a good idea...your secondaries working correctly? What power valve in the rear? My gut thinks a weak pump would show up farther down-track than in 2nd, but I'm sure Eric will correct me...

I tried a high flow pump from Carter a couple years ago in place of our stock AC...the A-B-A testing showed absolutely *no change* when swapping pumps...I may be jinxing myself here, but our 3700+ pound Camaro will trap anywhere from 117-118mph on our *non-sexy" stock pump.

[/ QUOTE ]

The carburetor is totally stock, so whatever it called calls for in the stock specs is what is in or on it.
I had it restored back in the very late 90's and then rebuilt in 2001 or 2002 when the cork gaskets dried out from the car sitting too much. The guy who did the work did not use cork this time.

[Mr. Chevy]

In addition to the above suggestions, I would also check your spark plugs.. I had a similar problem when I opened the exhaust up on a car and allowed it to breath better.. The car did not want to run above 3,500 RPMS without backfiring and missing.. Plugs can do funny things and act differently under different driving conditions or RPMS...

I would suggest running NGK plugs.. Guys on the site here convinced me and it was the best plug I ever had run.. I use them in both my big block motors..

Rich

[COPO PETE]

Thomas,
I would bet fuel starvation. The backfirk through the carb is a usual sign of that. I'm assuming 3/8 fuel line. I know in my 55 Chev,with the 5/16 line, that is the problem I had.
Also, what kind of ignition and what kind of gap on the plugs?
Peter

[Thomas]

[ QUOTE ]
In addition to the above suggestions, I would also check your spark plugs.. I had a similar problem when I opened the exhaust up on a car and allowed it to breath better.. The car did not want to run above 3,500 RPMS without backfiring and missing.. Plugs can do funny things and act differently under different driving conditions or RPMS...

I would suggest running NGK plugs.. Guys on the site here convinced me and it was the best plug I ever had run.. I use them in both my big block motors..

Rich

[/ QUOTE ]

I can get it to rev beyond that RPM range in first, so I do not think it is ignition related. I will not rule anything out though.

The one thing I did not try was to do the same "speed test" while driving along in 2nd or even 3rd and then going up one gear.

As I was doing this on a public road, I am always concious of trying to keep things resonably safe.

[Thomas]

[ QUOTE ]
Thomas,
I would bet fuel starvation. The backfirk through the carb is a usual sign of that. I'm assuming 3/8 fuel line. I know in my 55 Chev,with the 5/16 line, that is the problem I had.
Also, what kind of ignition and what kind of gap on the plugs?
Peter

[/ QUOTE ]

Peter,
Everything is stock specs except for the exhaust.
The plugs are AC, the points and coil are Canadian Tire (our Canadian members will know who they are) house items (Wells?) I believe.

I think it may be time to check the float settings and then go for another drive an do some more "troublshooting".

[StriperSS]

I remember years ago when I first put a Holley carb on one of my cars. At the dragstrip it pulled like a bear in first gear and then fell flat on it's face when it hit second, like it ran out of gas. It actually did run out of gas, but it was due to the carb itself. I think it was float levels. I haven't fooled with a Holley carb for years, but that's where I would start.

[mfchassisworks]

Some cars respond better or worse than others with the lack of fuel depending on the size of the shooters, accelerator pumps, overall gear of the car and the engine combination itself.

First you must rule out the fuel pump and its capabilities.

If you dont want to run a fuel pressure gauge make a temporary T-fitting install it as close to the carb as you can, get Autometer's copper oil pressure line, and get a small liquid filled gauage and install in on the end of the line. Run it up the cowl to the base of the windshield, under a wiper arm, or 200 mph tape it to the windshield where you can see it. Find a safe place to run through the gears, Then watch how low your fuel psi gets. You will be surprised. If you don't have always have 7psi then you aren't making hp. If you try to tune based off you plugs at the end of a run they will give you a false reading as the carb will seem lean but really there simply isn't enough fuel. No fuel means low hp = low mph.

During the test when the car stumbles or... and you let off note the fuel PSI upon recovery.

[JRSully]

get a hold of Eric @ Vintage (here on the site) I am sure he will diagnose correctly and you will be looking to kiss the ring shortly thereafter, he knows his stuff