ScottMH

i have a 1973 corvette with a rebuilt 454. it was rebuilt about 1000 miles ago. I have been taking it easy breaking it in. Today I decided to see what it could do today so I punched it and it pulled strong upuntil 4500rpms then it fell on its face like it lost all power. The carb is orginal but rebuilt. new fuel pump. new fuel lines. new fuel filter. it has the orginal dizzy with a pertonix points to electron ignition installed. The car runs great other than what happened at full throttle and it was only once it got to 4500rpms and it suddenly fell off the face of the earth. I also have a stock 4 speed with a new clutch. i am thinking fuel but with everything being new or rebuilt i just dont know. any ideas?

DRC

Ran out of power at 4500 rpm's or just died?

A stock 454 @ 1973 specs probably stops making power at around 4500 rpm's.

If you have a Pertronix III that unit has an adjustable rpm limiter, so maybe it is set to shut off at 4500 rpm's until you adjust it higher.

ScottMH

it kept running but its llike it lost power. i got out of it as soon as i noticed it stopped pulling. I am using the Petronix Ignitor I. as far as i remember it just bolted in place and slid over the shaft. no adjustments other than distance of the unit to the magnet. The 454 was built with a slightly more aggressive cam than stock and 9.5:1 compression. made 400hp and 500tq on the dyno with headers. I have the stock exhaust manifolds on it now.

BKbroiler

Could be a fuel flow problem. Carb float level or a pump problem. Could also be too much restriction in the fuel filter. I had to take the paper filter out of my Qjet due to fuel starvation like you describe. Engine would fall flat around 5K rpm but recover immediately after letting off the gas.

BOSTONCAMARO

It could be a lot of things...and I know I mention this a lot...but is the distributor in right? timing marks showing up? what is it timed at etc? many times a distributor can be dropped in so that a small or big block will run ok in that it doesnt pop etc, but installing incorrectly can cause the type of dogginess you describe..also check ignition as others advised, any pics of the car, pics showing the distributor etc

ScottMH

dizzy is fully seated and tightened down, timed at 36 degrees at 2500rpms with vacuum advance not connected.

GS977

it sounds like it's fuel related to me. what is the cam specs? i would install a fuel pressure gauge and watch it as i made another pull and see if it drops. i don't know what the mech fuel pumps run at but i run 6 1/2 on my elec pump and it doesn't drop. i also have a return style reg.
i don't know anything about quadrajets either, i always ran holleys too.
i'm sure some quad experts will chime in and help you.

aussiejohn

Scott,

Take out the filter in the carb and give it another run. If the result is the same, re-fit filter and look elsewhere. If performance improves, look for a better flowing filter in the line to the carb.

Regards from Down Under.

aussiejohn

ScottMH

i pulled the filter out and its not a paper filter it almost looks like a airator for a fish tank.

Les

Have you had a chance to see if it runs any better now? My first guess is fuel delivery too. If no improvement with this out, have you checked all the lines for crimps and kinks? I think somebody mentioned checking float level and that would be next on my list.

Also, a couple of quick questions-
At what RPM did the power peak on the engine dyno?
Was the dyno run done with your current carb and ignition combo?

HamadUP

Its sounds like you hit a valve float, check your valve springs. I had the EXACT same thing at the same RPM happened to my 454 few years ago, turned out to be a valve spring installed height mismatch, I added some shims (I used .060 shims under all of them to get the correct height) and the beast would hit 6000 RPM so easily, and it was still pulling, its amazing how a small clearance (.060 in.) would affect the performance of the engine.

MelWff

With the engine off and someone fully despressing the gas pedal see if the throttle is fully opening.

7T1vette

The Pertronix system requires a full 12vdc to feed the ignition circuit. If you installed it and just used the power wire going to the coil as the supply for the electronic ignition, that is your problem. That wire is a resistance wire, meant to limit the current that the coil receives.

Find another power source for the electronic ignition. The fuse panel has an empty connector labeled IGN that can be used or you can tap into that resistance wire immediately after it leaves the fuse block and run another [plain] wire {of appropriate awg size} from there and up to the electronic box.

If that Pertronix system is already powered with a 'straight' 12vdc, you could have a fuel flow restriction (tank, fuel line, pump, filter, or carb) or you could have a weak spark (caused by bad coil, rotor, dist cap, or faulty electronic ignition module).

ScottMH

ok after checking everything else ive decided to install a edelbrock fuel pump. question...how do they expect you to change the pump in car? is there a secert way?

RobRace10

I had the same problem with my 427, it would run out of fuel above 4,500 rpm. I removed the fuel filter in the carb and a new Edelbrock fuel pump solved the problem.

airtime

I changed my fuel pump in car several times but I have a tilt frontend and can get to bolts from behind front tire. I have the Holley rotatable pump but with the tight area it did not help much. Mine feels like u have pulled ur foot off the gas pedal when it runs out of fuel. I am gonna install an electric fuel pump. That will make it easier to keep the fuel lines straight and not all bent up to reach that fuel pump. I have a 489 also. My brother s. 72 454 would do the same thing as u r describing. Quit pulling but not fall on its face. He had the Holley carb and was rebuilt about like urs was. Ended up being he was running out of air from stock heads. Those heads will only flow so much air and since u have increased the power to more than double stock u maybe running out of air quicker than u think. His was between 4500 and 5000 ms

airtime

Rpms

BKbroiler

Have you tried driving it without the filter? A short test drive won't hurt and it might show that you don't need a new pump.

Les

I asked that question a few days ago but didn't get an answer. I also asked this, which I think could be pretty important.

Also, a couple of quick questions-
At what RPM did the power peak on the engine dyno?
Was the dyno run done with your current carb and ignition combo?

BKbroiler

I noticed that you had asked previously. Like you said, it still hasn't been answered.