1970 distributor-I'm finally stumped-help

I've owned this 70Blazer since '78. New "300hp crate motor in '98 with about 20,000mi on it. I'm running a Chrysler ballast resistor, having fried
the resistance wire some years ago, and it burns points frequently (after 5000mi or so). Now however, I can't get it to run right. It runs rough/backfires on acceleration in higher speeds. The timing is set at 10deg btdc at 700rpm w/vac line disconnected and carb (Rochester 4bbl) plugged. I've replaced the points/condenser, adjusted gap (turn to the right, then 1/2 turn back ccw. I've checked the plugs (autolite 145). Gap was .040, should be .035. I've replaced the centrifugal advance springs with stiffer ones and lighter ones. It was "pinging" upon acceleration, which started this whole mess. HELP
Do you think the wires could be breaking down, even they are "good" silicone and I don't see any breaks?
Could the dist be shot, sloppy, even though I don't detect any wobble? (I did replace the weights and noticed the posts were a little worn, but couldn't wiggle the shaft).
Are there any real mechanics (as opposed to parts replacers) out there with any suggestions? Coil plug wires Ballast resister plugs condenser (twice??)
Thanks in advance, LD
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I think you are getting much too "technical."
Exactly how much gap does a "1/2 turn" produce?
How far do you turn it to the right before you turn it back that 1/2 turn?
Couldn't you find a matchbook to set the points???
LOL!!!
Start with about .016" mechanical point gap - set with the points rubbing block on a distributor cam high point - then go for 30 dwell on a GM.
You can also set the dwell on any breaker points distributor at cranking speed. Just make sure the coil secondary wire is grounded so the coil "dumps" its primary, or you might get a false reading.
Bob Paulin - R.A.C.E. Racing Chassis Analysis Services
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Thanks, but I've done this method for 33 years. Turn cw til runs rough, then 1/2 turn cc (or vice versa). Set it in the middle between running rough, too close or too far apart, if you don't have a dwell meter. It's in the book (shop manual) I've not had a problem until lately, so I don't think it's related to the point gap/dwell setting. LD

get a little more advance/retard). That is, when I don't have my 1963, $1.97 Kmart timing light with me!! :-) LD

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This might be way out in left field, but how about the wire that goes from the points to the outside. I have seen them crack so they work fine at idle, but as soon as the advance plate moves, the crack opens and the engine misses bad.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
LD wrote:

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That's a thought. I had it break loose from the clip that attaches to the points one time, stopped me dead. Fortunately, I found it, fixed it and was back on the road in less than 10 minutes. I'll check that one real good. LD

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I've also run points for 30 years (ie: on a 76 Harley).
When the points get a couple years old they get harder to set and seem to wear out faster... I finally upgraded the Harley to electronic ignition last summer - and it still acts like the points are off a little - meaning that it's really something else (carb probably). Anyway, after trying every possible adjustment to the electronic ignition and timing I'm confident that's not the problem - set in the middle and live with it for now (do a carb or chase it more later). With the points I was never able to rule them out as a culpret to the engine studdering at 4K RPM (now the issue still remains but at least I know it isn't the points). Hope that helps, Elliott
LD wrote:

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It's probably your factory hydraulic lifters bleeding off. They weren't very high quality lifters in the late 70's.

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Why do you think it's in the ignition?.. what about fueling issues?
regards,
Jim
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Because it acts like electrical. It skips, runs "rough" like inconsistant ignition, spark to the plugs---not like a weak fuel pump/clogged filter, where it would try to cut out or quit altogether, esp. at high speed/rpm's. thanks, LD
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Why don't you save yourself a big headache and go get you an electronic ignition distributor ,loss the resistor and go fishing.
just my 2 cents Jeff
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wrote:

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wrote:

Been there, done that, on ( Dad's) '69 GM 307. Every 5000 miles it would blow the muffler off. You need to do a point resistance test (voltage drop from coil pos to battery ground) with points closed and ignition on. Anything over .1 volt is excessive. In my case it was a missing (from the factory) ground braid between the advance plate and the dist case. A bad ground wire is VERY possible. Mr Goodwrench failed to find the problem even after the 7th set of points. I was an apprentice at the time, and Dad got fed up with the truck and the dealer and asked me to check it out. Found the problem in less than 5 minutes, and fixed it permanently in another 5.

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To do an accurate bushing test:
Remove the disributor, and check for play in the top and bottom bushings. Sometimes the lower bushing can go, and the top have very little play.
as for the burning points, two words: "Mopar resistor!" they can fail to full voltage, do a voltage.
Also, check the polarity on the coil, posative to the resistor, negative to the distributor. That's not meant to degragate your abilaty, it's an easy mistake to make when your having other problems.
Good luck and I hope this helps.
Refinish King

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