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Old Problem

1967 GTX 440

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buffalo New York
I have 1967 gtx with 77 440 with edelbrock tm 7 with 750 holley and mallory unilite dist. Motor was rebuilt before it was installed. It ran good for about five years. Out cruising one night, ignition cut out and came back on, mufflers exploded. limped it home. new mufflers and msd distributor. Though it was fixed. Then had off line stumble and spark plugs started to foul. Check valve train with stamped rockers, no problems. Then took cylinder heads to machine shop, they changed valve springs and r & r valve guides. After reinstalling heads and tm-7 with holley, it never ran well. Now runs ok With edelbrock performer intake and 750 edelbrock carb but down on power. Also new plugs, wires and Carter fuel pump. New 3/8 fuel tank sending unit and 2 1/2 exhaust system last fall. Also last fall rear main seal and timing cover seal started to leak. Did compression test 125-135 psi. vacuum 18in at idle. Oil pressure 65 psi at idle.(has high oil volume pump since rebuild) Fuel pressure 5.5-6 psi What could be wrong? Thanks for the advice.
 
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I’m definitely not the expert here! But it sounds like you threw a lot of stuff at it without really knowing what the original problem was.
 
I’m definitely not the expert here! But it sounds like you threw a lot of stuff at it without really knowing what the original problem was.
Well the fuel pump went bad three years after the first problem. The tank sending unit quit last summer. The exhaust was 20 years old from the previous owner.
 
Sounds like an electrical problem to me. What does the spark look like at the plug? Nice blue spark? I’d check the bulkhead connections as well for corrosion.
 
I would be looking at the 12volt power supply to the ignition system and all grounds from engine and ignition system to begin with.
 
Ignition switch itself loosing contact after 50 years. We always replace everything else but forget to look at the first part. I spent lots of money trying to figure same type of problem only to have a old man tell me to look at the switch. After replacement voltage correct easy starts etc.
 
Is that a Performer, or a Performer RPM intake manifold? The regular Performer is known to be a non-performer manifold.

Anyway I'd check the ignition system as well...
 
This isn’t a “look at this / look at that” thing. You’ll need to be systematic. Being that it runs I’d start with ignition.

1) There’s some question about intermittent 12v supply. Put a test light Or multimeter on the coil, (pos) and turn on the ignition (don’t start). Have one person watch that while you wiggle every wire, connection, key etc. if it doesn’t drop out at all go to the next step.

2) What’s the initial timing? If you rev it what’s the final timing? It can be tough to measure the 38 degrees final you really want. You can mark the harmonic balancer 2-3/8” clockwise from the tdc Mark. That’s 38 degrees. Do you use vacuum advance? Manifold or ported?

3) if that’s ok. What do your plugs look like? Light tan? Are any different? Is the carb new? Factory jetting?

4) the throttle cables on these are made for a connection that’s about 1-1/8” from the throttle shaft pivot. Lots of aftermarket carbs like Holleys etc have a connection that’s farther from the pivot. This means two things. Floored often won’t actually open the blades all the way and with an automatic the downshift linkage won’t go as far as it should. Check that.

I’ll leave it at that for now. Tell us how you do.
 
This isn’t a “look at this / look at that” thing. You’ll need to be systematic. Being that it runs I’d start with ignition.

1) There’s some question about intermittent 12v supply. Put a test light Or multimeter on the coil, (pos) and turn on the ignition (don’t start). Have one person watch that while you wiggle every wire, connection, key etc. if it doesn’t drop out at all go to the next step.

2) What’s the initial timing? If you rev it what’s the final timing? It can be tough to measure the 38 degrees final you really want. You can mark the harmonic balancer 2-3/8” clockwise from the tdc Mark. That’s 38 degrees. Do you use vacuum advance? Manifold or ported?

3) if that’s ok. What do your plugs look like? Light tan? Are any different? Is the carb new? Factory jetting?

4) the throttle cables on these are made for a connection that’s about 1-1/8” from the throttle shaft pivot. Lots of aftermarket carbs like Holleys etc have a connection that’s farther from the pivot. This means two things. Floored often won’t actually open the blades all the way and with an automatic the downshift linkage won’t go as far as it should. Check that.

I’ll leave it at that for now. Tell us how you do.
 
12v at coil with key on, wiggle the wires at bulk head, coil and key switch no change in voltage. Timing 10 degrees advanced initial. 38 degrees at 2200-2500 rpms. plugs are ok but not tan. the carb was new with stock jetting. When throttle is floored its wide open at carb. I think the initial problem was the unilite dist. I tested the module and its dead. Thanks for the all the advice and great ideas.
 
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12v at coil with key on, wiggle the wires at bulk head, coil and key switch no change in voltage. Timing 10 degrees advanced initial. 38 degrees at 2200-2500 rpms. plugs are ok but not tan. the carb was new with stock jetting. When throttle is floored its wide open at carb. I think the initial problem was the unilite dist. I tested the module and its dead. Thanks for the all the advice and great ideas.

Hmm. That’s the usual stuff. Maybe you could explain in more detail what it does and doesn’t do. Drive normal but not great when you’re on it? How does it start? Auto or stick? What happens when you floor it from idle?
 
The cranking pressure is on the low side.
Of course that’s dependent on a lot of things....... but regardless of why it’s low.....there is probably performance left on the table with it being that way.

Warm engine, all plugs removed, battery charger hooked up.......
Test in 4 and 8 “pumps”.

If the new numbers repeat the old numbers(125-135), then it’s time for a leak down test of at least a few cyls.
If the leak down numbers are good, then it’s a problem in the “combination”(low CR, cam too big, cam not installed correctly, etc)
If the leak down numbers aren’t too good....... then you have to decide how to go about fixing it(rings or heads)....... or living with it.

This isn’t meant to address any issues with the car quitting, but more the perceived lackluster performance.
 
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