Starved For Fuel?
 

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?

Re: Starved For Fuel?
 

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... https://www.yenko.net/ubbthreads/imag...mlins/grin.gif

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.

Re: Starved For Fuel?
 

[ 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... https://www.yenko.net/ubbthreads/imag...mlins/grin.gif

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.

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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.

Re: Starved For Fuel?
 

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

Re: Starved For Fuel?
 

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

Re: Starved For Fuel?
 

[ 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

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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.

Re: Starved For Fuel?
 

[ 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

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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".

Re: Starved For Fuel?
 

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.

Re: Starved For Fuel?
 

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.

Re: Starved For Fuel?
 

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

Re: Starved For Fuel?
 

Thomas, if the AC plugs you are running are newer ones they are junk, believe me.. Thats what I was running and had all kinds of problems with them.. I threw mine in the trash, thats about all they are good for.. If they are old, NOS ones you should be OK...

I agree with Sully, if you want the carb. looked into contact Eric and send it to him for a rebuild or good check up!! Good Luck...

Rich

Re: Starved For Fuel?
 

First check the float levels.

Next, check/replace the fuel filters in the float bowls.

If the car sits for extended periods, you might check to see if the sock in the fuel tank is getting clogged or varnished up.

Eric

Re: Starved For Fuel?
 

I thought I had found the problem. The rubber fuel line which runs from the solid line coming from the tank to the fuel pump seemed a little long and appeared to have developed a slight "kink". It came as part of the fuel line kit that I installed over 10 years aago, so I never paid much attention to it.
I replaced it with a new and slightly shorter piece.

It took the car for a spin, and here is what I've found. The car "runs out of steam" somewhere around 4700 RPM, in any gear.

I have checked the float levels and they are okay.

Any ideas?

I was thinking of increasing the jet size in the carb.

Or...

Could it be an ignition problem like a weak coil?
The timing is set to 4 degrees and the dwell is 28 degrees

Re: Starved For Fuel?
 

It isn`t the jets. How about the valve springs? Try testing them for pressure.... may be float city... which could also cuase a backfire.

like someone mentioned....are you sure the secondaries are fully opening?

Re: Starved For Fuel?
 

What is the fuel pressure during a run through the gears?

Re: Starved For Fuel?
 

[ QUOTE ]
It isn`t the jets. How about the valve springs? Try testing them for pressure.... may be float city... which could also cuase a backfire.

like someone mentioned....are you sure the secondaries are fully opening?

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The engine was completely gone through shortly before I bought the car. I do realize that it is difficult to judge the quality of someone's work when the engine is buttoned up, but I find it difficult to believe that the valve springs could be an issue with less than 10,000 miles on them.
However, I have learned to never say never.

How would I go about testing the secondaries on a vacuum secondary Holley?

Just for the record, the people on this site have provided some great advice so far. https://www.yenko.net/ubbthreads/imag...ns/scholar.gif

Re: Starved For Fuel?
 

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What is the fuel pressure during a run through the gears?

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There is no easy way for me to plumb a fuel pressure gauge into the stock fuel line setup, so at this time this is still an unknown.
I may have to figure out a way if all else fails.

Re: Starved For Fuel?
 

[ QUOTE ]

It took the car for a spin, and here is what I've found. The car "runs out of steam" somewhere around 4700 RPM, in any gear.

I have checked the float levels and they are okay.

Any ideas?

Could it be an ignition problem like a weak coil?
The timing is set to 4 degrees and the dwell is 28 degrees

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Check to make sure your coil isn't wired backwards...car will still run, but takes a dump when under load.

Re: Starved For Fuel?
 

fuel filter in bowls if still equipped.
Float levels!! Does the carb have secondary jet extensions? If so it MUST use a notched float. I had a 69 camaro holley carb without extensions going 1080s 124 put jet extensions in it and fell on its face 900 or so feet. the rear float couldnt drop far enough to let enough fuel in to replenish what was being used. Put in notched float( i always run my holleys with fuel right up to bottom of sight plugs and just a littel tricle if you bump the fender)set level and 1 tenth better 60 foot and 1070 127 mph...
Ryan

by the way i Have a stock Y block that i drilled and tapped for 1/8 npt on the bottom side. ran my fuel pressure guage in it a few times to see what WOT was reading. after i was happy with that took off guage and put a 1/8npt plug back in that you cant see unless you take Y block off.

also i have seen the old fuel sending unit 'socks" melt into mush with age...did that get replaced??

Re: Starved For Fuel?
 

You mentioned it is a vacuum secondary..... Take a peak at the secondary spring. The real heavy ones will never allow the secondaries to fuly open. Try a trick kit and put in a yellow one....it opens fast and all the way.

Re: Starved For Fuel?
 

First:

What Eric said: "Next, check/replace the fuel filters in the float bowls." No one on here knows Holley carbs better than Eric.

Then, what Eric said next:

"If the car sits for extended periods, you might check to see if the sock in the fuel tank is getting clogged or varnished up."

It is a classic case of fuel starvation. Replace fuel filters first. If problem persists, remove the fuel filler cap, then remove the fuel line before fuel pump and blow a small amount of compressed air (too much and you could blow fuel up and out of the filler neck) which will dislodge any thing clogging the sock. Re-assemble and take it for a spin. If it is "fixed" then you need to remove the tank and the tank unit and either clean or replace the sock. Blowing back through it is only a temporary "fix".

Re: Starved For Fuel?
 

Just a thought, is the air cleaner clean?

Re: Starved For Fuel?
 

thomas,I would definetly trash the ac plugs.Had a similar problem on my stock 396 nova.changed to a NGK plugs;and the miss went away;by the way do you have a inline fuel filter;if so ;change it,besides, these two option only cost $30.oo or so.chris

Re: Starved For Fuel?
 

My L78 would take everything you could give it in 1st gear, hit 2nd pop and bang over 4000, same in third. Always the plugs.

Re: Starved For Fuel?
 

Thomas are you going to Cayuga this weekend? Look for the pure stock / FAST pits I plan on being there on Saturday BLUE COPO Camaro

Re: Starved For Fuel?
 

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Just a thought, is the air cleaner clean?

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Nope. That is clean.

Re: Starved For Fuel?
 

[ QUOTE ]
First:

What Eric said: "Next, check/replace the fuel filters in the float bowls." No one on here knows Holley carbs better than Eric.

Then, what Eric said next:

"If the car sits for extended periods, you might check to see if the sock in the fuel tank is getting clogged or varnished up."

It is a classic case of fuel starvation. Replace fuel filters first.

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At the recommendation of the performance shop I deal with, I removed the filters and am running without them for testing purposes.

Re: Starved For Fuel?
 

[ QUOTE ]
Thomas are you going to Cayuga this weekend? Look for the pure stock / FAST pits I plan on being there on Saturday BLUE COPO Camaro

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Unfortunately I only have time to go on Sunday.