Varying spark, out of ideas

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106 PSI compression!!!

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If you have a lean-burn distributor or a junker that you can lock everything out of, try that and see if it stabilizes.

I second checking the damper ring, and also....where did you get your parts? (don't say O'rielly or Autozone or Advance, please). I've had new distributors from AZ that had locked out advance cans and missing advance weights and all sorts of screwery.
 
jos51700 said:
If you have a lean-burn distributor or a junker that you can lock everything out of, try that and see if it stabilizes.

I second checking the damper ring, and also....where did you get your parts? (don't say O'rielly or Autozone or Advance, please). I've had new distributors from AZ that had locked out advance cans and missing advance weights and all sorts of screwery.
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Ok I won't say it but I couldn't find any other refurbished LA distributors in stock from Classic Industries or Year One. I still have the previous distributor that I can give another go.
 
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OK Have a finished Dist list. Still doing inventory after Carlisle. All are completely disassembled all tolerances check, ant item fixed reassembled and run on a sun distributor tester to document the curve either factory or custom. Also have tons of pre 90's ignition parts if needed. Some...
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halifaxhops said:
Interested to see what the fix for this is.
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Today after work I'm planning to put the old distributor on and see what happens. I recall I only replaced it because the advance canister leaked and I couldn't source just the canister, and could only find a distributor from AutoZone in stock. Every test I ran on the new distributor has been fine though. I've had the varying spark problem for a while and can't recall if I had it before the new distributor.
The low compression does have me worried. Once I get it to idle fine I'll run another compression test. I may just need to have the engine rebuilt.
 
The timing should still be stable even if it needs rebuilt. If the damper hasn't slipped, it could be the timing chain slop but that doesn't sound terrible.
 
Well, I scavenged the vacuum canister from the new one and put on the old one back on, setting the point gap again first, and she's running about as good as I've ever seen her. Ignition timing stays pretty steady. I guess I can call the new distributor a dud.
I started to run a compression test again and was getting similar numbers. I am hoping it's because it's a cheap gauge and/or user error. The engine still has a hesitation issue that's remained throughout quite a lot of work, too, but I'll take it.
 
Centri weights were probably advancing/moving around in the new dist.
 
Traxfish said:
I've had for a while a problem with varying spark timing and it's been getting worse, varying about 3-4 deg each rotation. Now the engine runs pretty poorly at idle and does not get better with RPMs.

I've put on a new distributor, cap and rotor included, and just checked point gap again, setting it to .018.

I put on a new coil and new wires.

I thought I had diagnosed a timing chain with weak stretch, as it had all around low compression (106-122 psi) and varying spark timing. I read of a way to test chain stretch without removing the cover by counter rotating engine twice stopping at TDC, then rotating the engine until the distributor rotor moves and measure the degrees it took. Supposedly 7 is ideal, 10 is limit of acceptable, and I measured 12 degrees. So I then did a timing chain replacement and the engine is not running better. I've not checked compression or timing chain stretch since however.

What else could be the culprit?
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What about wear in the distributor shaft bushings. With the cap and rotor off try wiggling the shaft to the front and rear and left and right. It should only have .002" clearance. Hardly enough to feel. If the bushings are worn, the shaft can flop around causing timing to jump around.
 
Not the same timing problem but,, I had a similar low compression on a slant. The previous owner installed the timing chain 1 tooth off and drove it for years that way. Really rich and really low power. The rings, valves, etc... had tons of carbon build up. A LOT of blowby.

After fixing the t-chain, this isn't an add, but I happened to watch a YouTube video of a dude using Berryman B-12 (similar to seafoam but better in my opinion) to get his sealing rings unstuck. I put some in thru the spark plug holes, let it sit, some more in the crankcase, ran till warm, cool, ran till warm, then changed the oil. It actually worked. Went from 100-110 to 150 average and the blowby isn't an issue.

Not saying it will definitely work for you. If the rings are indeed worn badly then rebuild for sure. 1 can of Berrymans is worth a shot though.
 
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