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Old 05-01-2013, 11:16 AM
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1974 pontiac 400 big block WONT start

So I recently bought a 1977 Firebird Formula, with a 1974 pontiac 400 big block (got the year off the rear engine code). It ran okay okay when I bought it and now it wont start.
The engine has HEI, a edlebrock performer pontiac Intake, and stock carb (for now).
The engine fires a bit then the starter disengages (really annoying), but just does not want to run,

I checked the timing and spark plug wire configuration, that is good. Gaped the sparkplugs to .04". The distrubutor cap is new, wires are yellow accell and look in good shape..

Does anyone have any experiance with these engines and some sugestions? Thanks
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Old 05-01-2013, 11:41 AM
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That might be the saddest looking engine compartment I've ever seen. If that's indicative of how you run your operation, it's no wonder to me that the motor doesn't want to run. When's the last time the motor got new spark plugs? How long have those plug wires been on there? Have you monitored the fuel pressure at the carb? Cleaned and/or replaced the fuel filter? Set the carb float? Have you ever done a compression test on the motor or had a vacuum gauge hooked up to the intake manifold? Sad lookin' deal Jo-Jo.
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Old 05-01-2013, 11:42 AM
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Fuel in tank
12.68 volts key-on
oil in crankcase


Did you take the plugs out and verify the sparkl at the trode?

Then with a finger in the hole bump the engine and cinfirm compression? Better yet compression gauge, shrader valve in.

Then look for fuel cranking into a bucket.

Connect the carb and swab to see if the needle coming off the seat. Look for accelerator pump function and the pump shot in the primary/front carb barrel.

Cold time engine from true TDC.
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Old 05-01-2013, 12:03 PM
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Ya I just bought the car... It has never been restored or refinished, you can't expect a old car from 1977 to look new under the hood lol.
The plugs looked okay when I gapped them, but I'll try some new ones in there.
No compression test or vacume test done yet, maybe I'll do that tonight.

She's deffinatly a fixer uper car,
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Old 05-01-2013, 12:08 PM
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Quote:
Originally Posted by Chad1965 View Post
So I recently bought a 1977 Firebird Formula, with a 1974 pontiac 400 big block (got the year off the rear engine code).
Also, there is no such thing as a Pontiac "big block". All Pontiac blocks are the same. The 265 and 301 just had shorter decks along with the Ram Air 5, that were special built race engines.
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Old 05-01-2013, 12:10 PM
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Quote:
Originally Posted by spinn View Post
Fuel in tank
12.68 volts key-on
oil in crankcase


Did you take the plugs out and verify the sparkl at the trode?

Then with a finger in the hole bump the engine and cinfirm compression? Better yet compression gauge, shrader valve in.

Then look for fuel cranking into a bucket.

Connect the carb and swab to see if the needle coming off the seat. Look for accelerator pump function and the pump shot in the primary/front carb barrel.

Cold time engine from true TDC.
Did not verify spark on electrodes, i'll try that tonight with new plugs,
and a compression test!
Ya did the timing by takin out #1 plug, saw the piston was at highest point, timing mark on balencer was at 0.. ect

Thanks for the ideas! I'll give them a try tonight.
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Old 05-01-2013, 09:45 PM
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Wow it has a 90 amp alternator on it too. Whoever you got it from was not the best at working on it.

Last edited by Thumpin455; 05-01-2013 at 09:51 PM.
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Old 05-01-2013, 10:51 PM
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Hi
Just looking at spark plug wires won't tell you anything
you need to check them with a ohm meter. Or stick your finger
in the end of the wire while someone cranks it. just kidding
Another thing. I'd look for a shroud before summer get's here.
Rich
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Old 05-02-2013, 08:40 AM
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should be a 4 speed car.
its kind of apperent that the carb is leaking on your new bright shiny intake manifold.
im no professional, but i would start there. you know, with the obvious things.
just remember, it only takes a roll of 1200 grit to polish a turd!
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Old 05-02-2013, 10:47 AM
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How long has it been since it last ran ?? Could the gas have gotten stale ? Moisture under the cap from temp changes ? I would find a better starter so it will turn over beyond a couple fires before the bendix kicks out.
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Old 05-02-2013, 11:06 AM
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Well got a new fuel filter and spark plugs in last night and did a cold compression test (really cold, -10 degrees, no heat where the car is!) they were all around 115 psi.
It kinda ran for about 20 seconds. Sounded like not firing on all cylinders! I checked the rotor cap and there are white powder burns on the inside (dont know what that is about).
Im gonna check the wires like suggested or get new wires . Also getting a good carb on friday, so hopefully some progress can be made friday night!

Thanks for all the good sugestions!

As for tonight back to work on my 51 gmc
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Old 05-02-2013, 11:31 AM
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That white powder is from moisture corrosion. It is blocking some of the current to the plugs. Scrape it off. Also, check the center carbon button. When the powder blocks the voltage, it backfeeds into the button and can burn it off in the cap. There is a silicone washer and a spring under a cover that the button comes out of. Remove the rotor too and see if the backfeed has burned thru to the shaft.
AND while you have the cap off, check the 2 little wires coming out of the pick up coil. They get brittle and break when the advance moves. They cause intermittent running issues and false starts.
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Old 05-02-2013, 01:48 PM
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Ditto to what TMP has just said.
HEI are infamous for burning a hole right through the rotor, so the spark goes directly from the coil to the distributor shaft.

Why?
It takes the path of least resistance. If there is corrosion build-up on the dist cap terminals, or bad wires, or bad plugs.

I'd also recommend the better quality cap and rotor with BRASS rather than aluminum contacts.

If the cap and rotor don't fix your problem, and you still have intermittent or no spark ... the ignition module is a fairly common culprit.

If you replace that, be sure to use the dielectric compound which is (or should be) supplied with a new module.
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Old 05-06-2013, 09:30 PM
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Alright so I got it running tonight! The weird thing is that the timing Haas to be retarded 15 to 30 degrees for it to run (that's without the vacuum advance hooked up). And it does not idle very well I have to keep giving it gas to run but its runs nice with good thotlle responded when I'm on the gas.
I bought a holly 750 Carb off a guy that used it for a dyno run on a smc stroked so I don't know if that is why it won't idle well?
Has anyone come across that timing issue before?
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Old 05-06-2013, 09:57 PM
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You mean advanced 15-30 to run right?

Do not get on it , until it is tuned. With the carb at a manufacturer suggested baseline get the timing set first.
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