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Ignition stumble after removal of smog harness..


eurotrash
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My car has been a rock solid runner until today.. After a stop for gas, I noticed an intermittent lurch, or stumble, when cruising at about 45.. Then found it to happen through all RPM ranges..?! I removed the smog harness and ran the wire from the 12th fuse to the coil just last week. It has a stock black coil and pertronix..

Example: at idle, the tach sets at 0 unless I hold the revs up a touch. This is what it does at that point:

http://www.youtube.com/watch?v=kQWmFLg-DLQ

I checked the new connection at the coil, the coil was bordering on hot-to-the-touch.. I don't know what is normal there..

I'm not sure what to do at this point, I'm at your mercy.

Any ideas gents??

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I'm running a weber 32/36 with standard points and condensor. I had the same problem when I desmogged my '76. The problem was tracked down to an incorrect vacuum source for the distributor advance. HTH

Distributor has to be on ported vacuum, not direct manifold vacuum. If it is plugged into the manifold remove it and look at the vacuum nipples on the carb. There should be a small one about midway up. Thats ported vacuum

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Good suggestion guys. So, I went out and looked at my vac. advance situation..

Well, I found that I had detached it and blocked off the ports when I was tuning for the synclink.. So I re-plummed it to the lower/smaller port at the carb (the charcoal cannister is on the top/larger port) and fired her up. It idled dead nuts smooth at 900 rpm! So I took it for a spin, and when I parked it, it was better at idle but the fluctuation is still there.

Shucks.

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Are you running 12v straight to the coil?

I think the black coils want somewhat less than 12v to run. (9.x?) 12v only for start-up.

Earlier models had a ceramic ballast resistor, later models had a resistor wire to coil.

Blue coils want 12v all the time.

Probably not related to your issue, someone will correct me if I'm wrong.

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Are you running 12v straight to the coil?

Earlier models had a ceramic ballast resistor, later models had a resistor wire to coil.

Blue coils want 12v all the time.

I haven't tested the current voltage. I just ran the wire per the FAQ. I actually paused when I detached the clear resistor wire because it concerned me. I looked at reusing it, but it didn't go to the fuse box and I deemed it too short for my needs and shrugge it off. Maybe this at least explains the temperature of the coil itself????

Maybe I should look at a blue coil (or the little MSD Streetfire box) for a replacement if resistance turns out to be the issue...

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Not to hijack this thread but... can someone explain to my feble mind what is happening when you remove the emissions Loom and replace it with a single wire from #12 fuse to + side of Coil?

I have removed all the wonderfull hardware stuff and left the loom taped up and secured to the firewall. I'm to big of a chicken to take the last step until I understand what goes on.

Thanks

Rich

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I was planning to pull out the wiring diagrams this weekend, beat mt head against the firewall, and try to learn something about the relationship between the + coil terminal, the emissions harness, and the #12 fuse block.

I can't wait to hear how this sorts out.

Rich

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Upon further inspection and stripping of the harness, the green runs to the relay box first, then to the fuse box.

So I just cut the resistor wire off and wired it in in it's full length. Testing revealed the following:

Key off: 0 bolts at the coil.

Key on: 12+ at the coil.

Motor running: 12 at the coil.

Addition of resistor wire:

5+

8.95+/- ..respectively.

I have no data from when the harness was fully installed..

And the stumble is still there. Moving in to the carb after a test drive.

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Gutted and cleaned the carb. New needle valve and readjusted the floats.

The stumble is still there and gets worse the more I drive it. Could I have damaged the coil?

Oh, and now it runs very rough and the third cylinder is getting no spark. When I pull that plug wire, its the only one that makes no change in the running condition.

I'm lost..

I'll inspect and clean the pertronix unit I guess..

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