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Author Topic: Spark Knock  (Read 4193 times)
L78 steve
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« Reply #15 on: April 16, 2010, 09:19:44 AM »

The light throttle ping is usually caused by total timing, including full vac. advance which can be up to 50*, 36+15=51 degrees. Try with the vac. can disconnected
and see what happens. If it solves your problem you can shorten the slot and reduce your vac. advance some. You may want to invest in a mity vac (hand vacuum pump) also.

69 Z/28 Dover White X33,ZL2,PS,M20,
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B
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« Reply #16 on: April 16, 2010, 09:52:19 AM »

The curve is probably wrong for the current initial setting. Easy shade tree check method/fix. You can mark your total timing point on your balancer with a sharpie and you do not need to purchase anything.

Use a cloth sewing measuring tape, a piece of string, whatever. Just wrap it all the way around the balancer with "something" then lay it flat to measure the balancer circumference with a common measuring tape. You multiply this mesurement by .1 to get the distance from the timing mark (slot) to the target of 36 degrees on the balancer. That sharpie mark you add will be on the balancer to the RIGHT of the TDC slot on the balancer.

Disconnect the vacuum advance (plug the vacuum leak). Hook up the common timing light and shoot the balancer while you rev the engine up until the ignition stops advancing, maybe 3500 or 4000 rpm or where ever it stops advancing. With the light flashing and distributor at full mechanical advance you rotate the distributor to line up the sharpie mark with the "zero" on the timing tab pointer then lock down the distributor. Hook the vacuum advance back up to a manifold vacuum signal.

You will probably need to play with the RPM screw on the carb at this point to get it to idle right because your inital advance will likely be much less than it was when you started. Where ever the advance is now is where it should stay untill you can recurve the distributor properly. The distributor will need to modified to remove the available centrifugal advance (reduce slot travel) in order to PROPERLY run additional initial advance that the engine will "like".

A properly recurved distributor will allow you to run more initial, start the centrifugal advance no sooner than 1200 RPM and finish advancing at about 3000 RPM.

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« Reply #17 on: April 16, 2010, 09:28:22 PM »

One fact I should have stated. Eric Jackson at Vintage muscle car parts rebuilt my distributor. So I would guess it is done right. He is a sponsor and active on the Yenko board. He rebuilt my carb and did a good job.

I will map the timing.



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« Reply #18 on: June 14, 2010, 10:05:35 PM »

My 69Z is experiencing slight spark knock under aggressive aceleration. I am burning 93 octane, my air/fuel mixture on the carb is dialed in, my timing is 10* at 900 RPM. The motor was rebuilt when I bought the car so I don't know a lot about it. I have recognized that the car seems to run with limited to no SK with the breather assembly off. Maybe just a coincidence but this did happen. Also, I have noticed at times when I get 93 octane as some stations the fuel quality will vary. If I put 100 octane in it runs great. Just wanted to see if anyone else is expericing anything similar. Eric Jackson at Vintage Muscle Car parts rebuilt the Carb.


What cam? A DZ at 11:1 with 30-30 cam replacement (not a new "modern fast ramp cam) should run with aggressive timing on 93 easy.


Lemans Blue X33. DZ, M20, manual steering. Only BU code rear end is original.
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