Hi all.

First up, I have been in California for 7 years after moving here from Australia and I'd like to say what great place California/ USA is, It's really similar to home except you guys have a funny accent and have the driving all messed up with the side of the road deal, but all is right now, as we say "Bob's me uncle"

The first time I drove a manual( stick shift) car here, I almost opened the drivers door!! ( You can laugh now!):yes:

I own a 1970 Impala Custom which we have tubbed using a 9" with 4.11 gears,and have just installed a 406sbc. This work has been done by my mate and I here in Riverside California and have done some serious cruising and strip miles with her. The old motor was a 350
The 406 has been good,,I only have around 120 miles on this new motor and I have a small problem that I hope someone can help me with. I have an HEI on it( from the 350 installed by me after switching from points) and i am not sure if it's the problem I have.I run 12 intial which is around 34 at the top
Seems when I get to around 160 on the temp the motor runs on 7 cylinders, but if i plant the right foot,,the old girl comes to life without any hesitation. Seems around 2600-3000 rpm this problem occurs.
I have pulled the plugs, all look perfect, have hooked the pick-up from the timing light and I get a good flash from all wires. BUT, when I remove the wires from the cap, seems like there is no difference when removing #1 and # 8, the others have a noticeable drop in rpms.
We thought maybe an engine balance problem, even though I had the motor externally balanced, so to test this, I unbolted the torque convertor, and also removed the belts on the front so all I had turning was the motor itself. Still this problem was there. I have even tried running on primaries to see if it was a hesitation between the 4 barrels,,,but still no different.
Engine specs
SCAT9000 crank
the correct harmonic balancer( big one) and the correct flex plate. These are new items and are both balanced as per the manufacture's specs.
When the motor is cold,,she runs and drives 100% perfectly,,,once it has around 3- 5 miles on it,, this annoying little problem creeps in. Plenty of power just acts like on 7. When the temp is 180ish,, then it is rough at the take off too,,,like seriously on 7 . Any ideas?
I tend to think its the HEI, but not sure how and where to test it. It's 50,000 volt Procomp bought off Ebay ( dime a dozen there,,,you'll see it there if you do a search, everyone seems to have the exact same one there!) and I am not sure if thats the problem to be honest. The HEI would have around 500 miles on it between the 2 motors.
I doubt that there is a problem with any balancing as all the right stuff is at both ends of the crank, plus, the problem isn't there until the motor is around 160 on the temp gauge.

Any thoughts?
Let me know if any more info is needed.
Thanks a bunch in anticipation of the help I need.
Kind regards
Michael "dingo" Boemia

Like you said, "dime a dozen". Just grab someone else's dist and give it a shot. Maybe your "mate" drives a Chevy. Surely he doesn't drive a Ford?????? Might not be the exact curve your looking for but it will show up the problem if there is one there. Other than that, you aren't using the original "coil" wire to power the HEI are you? Should have at least a 12ga "real" wire going to the IGN terminal on your fuse box. Low voltage and heat could cause weird things to happen. Also be sure you have a solid ground between engine/chassis/body.

Is this engine carburated or injected? I have seen injected engines run great when cold but the injectors start shorting out as things heat up. How about plug wires? Are they old? If they are shorting out and losing voltage that could be a problem. Wait till dark, fire up the engine and spray the engine compartment with a windex bottle, or other spray bottle, filled with tap water. If your wires are leaking voltage it will look like a thuderstorm under the hood.

Thanks for the quick replies,
My mate is a chevy man, so good point re; his dizzy,,, sometimes the obvious solutions can be found when others do the searching!!
It has a 750 DP Mighty Demon, is as crisp as can be. The point made about the ground strap between motor and frame is a good one too,,I haven't got that,so I'll try that and let you know. It has a heavy IGN wire too,,so I know that's ok in that department.
Again thanks for the replies, any other thoughts would be greatly appreciated too.
Cheers!!

check the valve lash. if they are set tight while cold, then they will be tighter when hot (maybe staying open a little on a couple cylinders), then try a compression test while hot.
lastly i'd try a different ignition module. HEI's like to eat them.

There is a ground strap/wire inside the cap where the coil mounts. I have worked on cars with a problem like yours and found that the coil ground was missing. Problem went away after it was replaced. Another customer stated his truck would quit only when it was put in reverse in the afternoon. I was able to verify the complaint and after a lot of head scratching it turned out to be the module.Modules are cheep, maybe try a new one or a good used one and make sure you apply the grease that comes with it.

Mate are you on a boat....Ahoy Matie...JK

Well,,you made me laugh,,,keep up the good work,,I think!!
Take care

Thanks for all the tips and suggestions,
1 question though, This so called ground strap under the cap by the HEI coil, where would the wire connect to if I don't already have one?
I'll have a few things to check this weekend and I'll let you know how things go!!

the wire harness that runs from the cap to the distributor body has 3 wires. (or it's supposed to) There's supposed to be a metal strap gizmo that connects the metal frame of the coil to the center of the three wires. You should be able to see it if you lift the coil cover. As long as you're there pull the four screws that hold the coil in, lift it and look underneath. There's supposed to be round rubber gasket with a carbon contact underneath. the bottom of this gizmo is what the springy thing in the center of the rotor contacts. All this stuff needs to be in place. Also, check that the distributor cap is mounted correctly, it's possible to get it on crooked and have problems with the rotor tip getting broken.

Did you double check that #1 and #8 are not reversed at the cap? Easy to do along with #5 and #7.

Some photos to illustrate what Tom is talking about.

http://i80.photobucket.com/albums/j199/64elcamino/groundstrap.jpg

http://i80.photobucket.com/albums/j199/64elcamino/coil.jpg

http://i80.photobucket.com/albums/j199/64elcamino/P8250010.jpg

Great info all,,thanks again,,,I'll let you know what I find.Way too cool
Thanks again
Regards Michael