Breaking Down

[Ronald L.]

Re: Breaking Down

Update - points, cap rotor, capacitor and condensor were all changed.

Has the LecLim new wires, original coil.

Still breaks down.

[William C.]

Re: Breaking Down

Have you checked to make sure the moving plate in the distributor (the one the points are mounted on) still has it's ground wire intact and connected? (goes under the vacuum advance screw) Have you tried a set of SP wires made from a reputable aftermarket source? Delphi (the old Packard Electric) exited the ignition wire business a few years back, I don't know where LL is currently acquiring SP cable from.

[Ronald L.]

Re: Breaking Down

Yes, the ground screw is tight and the other end appears solidly crimped to the plate.

Thinking the coil - any ways to verify coil function or who makes the exact copy of the original?

[Clem Z.]

Re: Breaking Down

Yes, the ground screw is tight and the other end appears solidly crimped to the plate.

Thinking the coil - any ways to verify coil function or who makes the exact copy of the original?

unbolt the ground wire and use a ohm meter while pulling on the wire to make sure it is not broken internally

[William C.]

Re: Breaking Down

To eliminate the coil or confirm it, I'd first run down to the NAPA store or Advance or whomever is the local parts store in your area and just buy a replacement. Swap it in and see if the problem goes away. If it does then you can contemplate either a NOS or Reproduction coil for permanent use.

[Ronald L.]

Re: Breaking Down

New coil, still breaking down, getting into it, sputters, pops out the left exhaust. One of those "NEW" lectric limited wires bad? What else could it be with dwell & timing - right on?

[Duke W.]

Re: Breaking Down

I don't know what lectric limited wires are, but there have been a lot of reports than "reproduction, date coded" wires are junk.

You can measure end to end resistance and it should be no more than about 5K ohms per foot. Wiggle the wire while checking them, If the ohmmeter jumps around, the wires are defective.

Duke

[Terry D.]

Re: Breaking Down

What plugs are you running? If you run it hard after break up does it clean out or break up every time?

[Ronald L.]

Re: Breaking Down

Here is the latest:

I measured each LL plug wire, long ones 12K ohms, short ones 9k ohms, no change on wiggling the wires.


I changed them back to the Yellow Mallory Silicone Copper core Wires that measures 0 ohms.

The plugs - all were at .035 gap, carboned somewhat R44N.

Got it out - we are not talking hard run for a 390HP motor, just getting into it and it does not pop at 2500, but does sputter towards 3000RPM, mostly left side.


Seems to be very slightly better, twiddled with the non stock 800cfm Holley in the process and it is now kicking out some carbon smoke too.

Any ideas?

[Duke W.]

Re: Breaking Down

Now that you have eliminated most ignition system possibilities via parts substitution and 'fessed up that you have a non-OE carb. It's time to look at the carb, but you should also state any other modifications. Inlet manifold? Camshaft?

Typical aftermarket "one size fits all" carbs can be very difficult to set up. The Chevrolet engineers spent a lot of time tuning carbs to each application - jets - both idle and main - metering rods (if equipped), and air bleeds, not to mention choke and fast idle cam calibration.

This is why there are so many OE carb numbers.

Duke

[Ronald L.]

Re: Breaking Down

Only know mods are the Edlebrock torker 2 intake and 800CFM Holley.

I have the original manifold and carb in boxes, was going to wait a year or so to change those back.

Any thought this could be weak valve springs?

[Michael G.]

Re: Breaking Down

Ron,

Good day. Let me throw in my 2 cents as every one has taken their best guess from a distance. No one without being there examining, calulating, deducing, subtracting or proding can possibly determine what the issue might be with your engine. Rather than burn up a great deal of energy gathering up varied opinions of "what may or might be the issue"......turn the car and engine over to a know competent mechanic with experience in like kind engines. One might get lucky and find the culprit however luck would be the key word here. Don't get me wrong, I say these things in all due respect. Should you not be able to deduce the issue yourself, rather than shoot for "best guess" let a qualified/competent mechanic look it over.

[Duke W.]

Re: Breaking Down

Only know mods are the Edlebrock torker 2 intake and 800CFM Holley.

I have the original manifold and carb in boxes, was going to wait a year or so to change those back.

Any thought this could be weak valve springs?

IIRC the Torker II is a single plane manifold, which is a very poor choice for a road engine. Also a carburetor that is calibrated for a dual plane manifold usually needs to be recalibrated to perform properly on a single plane manifold.

Since you have the OE manifold and carb, rather than waste more time on the installed bubba setup, reinstall the original induction system and spend whatever time/money is needed to get it running properly.

If you do a basic carb overhaul/zip kit on the Q-jet, it will probably work just fine.

It could be a valve spring issue, however, if you are not aware of the problems with early big block valve springs, you should do a search and while you're replacing the induction system, look at your valve springs, determine what they are, and if they are the first design single spring/damper, get a set of second design dual springs and install them.

IIRC the idle behavior of the 390 HP engine should be about 14-15" Hg. manifold vacuum at 600 in neutral, but a 390 or 400 HP owner should verify this.

If your idle behavior is not close to OE then you probably have a bubba camshaft, too.

It's very common to have various driveability problems with vintage Corvettes because most of them spent some time with bubba over their lives and got all screwed up.

Duke

[Ronald L.]

Re: Breaking Down

Duke, thanks for your expertise.

I'll do the compression check Monday and move on. While this set up starts in a snap, barely a touch to the switch, removing the simpler bubba stuff has introduced part of this stumble that I did not notice last year.

I have pictures with the valve covers off, they should tell us something tonight about those springs.

[Ronald L.]

Re: Breaking Down

Duke

Compression test results
1 190
3 195
5 180
7 200
2 195
4 185
6 200
8 200

I looked close and photographed the visible portion of the valve train, not abnormalities noted - stuff looks clean. I can send those photos to you if you wish...