327 randomly runs bad

[Dead Parrot]

Something that happened to me is the mechanical advance occasionally sticking full in. Could lead to bad performance if you adjusted your idle advance when it was stuck full in. When it snaps back to off, you are now probably ATC on idle timing. Or if initial timing correct, all of a sudden you have an extra 12~15* or so of extra idle timing when it sticks on, which will cause a higher idle speed.

Check idle timing when it is running correctly, then check when idle sticks high(you may have to roll back the idle throttle screw to make sure the RPMs are below where the mechanical advance should start coming in). If your normal idle timing now has +14 or so extra, stuck mechanical advance.

[tdangle]

I think you need to focus on the HEI dist. I had the same type of problem years ago and it ended up being the center button of the HEI cap not springing down and making contact with the rotor. Not sure how it ran at all. I would look in that direction. Also for carbon tracks in the cap. If the electronics of the HEI were bad, I'm pretty sure it just wouldn't work at all not be intermittent. Follow the spark path from the coil (in the cap) to the rotor and to each stud (going to each plug)

Good luck and let us all know

[Port&PolishMan]

Originally Posted by geezer#99

Valves won't do that intermitent thing.
Leave them alone for now.
No electric fuel pumps either unless you install a fuel reg set at 5 psi. In fact you might need a reg anyway.

Try this instead.
Initial timing at 14 degrees, hook vac advance to manifold vac port and turn down your idle to 700 rpm or less.

Sounds like you're just on the edge of kicking in the mechanical advance since the rpm goes up and down.

+1

** Test with the Fuel Cap Off ** might just be something Simple . .
I also found a Cracked Plug on My Motor ..Hairline Crack - till I stressed it Broke easier then Tooth Pick ..

[kaycee]

Did it start with the "FRESH" tank of gas may drain it and put 5 gal of different gas in and try it . Coils usually just go bad and not intermitant like your having ,but we all know IT COULD HAPPEN .

[lumpy63]

what type of choke do you have? manual or electric? Is it hooked up correctly? Sounds like fast idle cam on carb to me.

[JPBrecheisen]

Had a very similar issue on my 72 K25. Could have swore it was fuel related, but ended up be a bad ignition condenser.

Problem came and went like flipping a switch.

Based on the symptoms, I suspect a malfunction of the ignition system.

[Ken B]

Originally Posted by tdangle

I think you need to focus on the HEI dist. I had the same type of problem years ago and it ended up being the center button of the HEI cap not springing down and making contact with the rotor. Not sure how it ran at all. I would look in that direction. Also for carbon tracks in the cap. If the electronics of the HEI were bad, I'm pretty sure it just wouldn't work at all not be intermittent. Follow the spark path from the coil (in the cap) to the rotor and to each stud (going to each plug)

Good luck and let us all know

This is exactly where I would start as well...

[luvbowties]

Fuel pump pressure must be max of 4-5psi for Edelbrocks. But, eliminate vacuum leak FIRST--you said you do cheapest checks first. Bet you're gonna find a vacuum leak around base of carb to intake--esp. if you are using some type of adapter. Else, along intake-to-head gasket.
Just another 2 cents worth for free.
sam

['63MurderTruck]

Checked my voltage...

Voltage at the battery is 12.7V, the voltage at the wire that feeds the HEI is 12.4V, but drops to 9.6V while cranking

So, I 'm going to work on my ground. Right now I just have a ground from the battery to the block, so now I'm going to run a ground from the block to the chassis.

I also bought a new 4GA hot wire to run from the battery to the starter.

I'll see if any of this helps

If my battery is 12.7V, what should it drop to while cranking(minimum)?

[Captainfab]

What is your electrical system voltage with the engine running? It should be 13.8-14.2.

['63MurderTruck]

I'm not sure, I'll check it tomorrow when I get it running. I'll post it here.

Originally Posted by Captainfab

What is your electrical system voltage with the engine running? It should be 13.8-14.2.

[Dead Parrot]

The 9.6v seems close to normal. A quick google of Cold Cranking Amps shows that standard is the number of amps delivered at 32*F while battery voltage is at least 7.2V.

Double check the suction hose from the gas tank to the metal frame line and the suction line from frame to fuel pump.

I know conventional forum wisdom is the Edlebrock 1400 series carbs 'require' a pressure regulator to avoid flooding but I have a 1405 on my 75 and have never had or needed a regulator. Been through 3 mechanical fuel pumps in the last 20 years. I did set the float levels before initial install. Mine could be the one at the statistical end of the bell curve.