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Discussion Starter #1
I'm stumped now and looking for insight. My car knocks a lot when the vacuum is connected to the distributor, not so much if capped off.
I have tried setting the initial timing anywhere from 6 degrees to about 15 and if I get on the gas it starts knocking loudly around 2500 rpm and continues until I've heard enough, usually around 4000 rpm. Going up a hill in top gear where I'm turning about 2200 rpm will cause some knock too. Yes, I disconnected vacuum to set the timing.
If I completely disconnect the vacuum and cap off the ports then I get a little knock at high rpm, say over 5000.
I have tried this with vacuum connected to the carburetor and lately using a manifold fitting.

I have a 1971 302 with Street Dominator manifold and a Carter AFB, Duraspark ignition including distributor and coil. The distributor was new/rebuilt from Autozone a few years ago when I installed the DS, since the junkyard car I took it from was a 351. I have a couple spare DS boxes in the garage, I pull the blue strain relief version whenever I see one at the junkyard.
 

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vac advance will only make a difference during light/part throttle. once opened up the mech adv takes over

Id have your dizzy properly recurved by Dan @Glazier Nolan
 

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Vacuum advance, ported or manifold, is the same at part throttle. What is your total advance at 2500-3000 RPM? You can check this with a timing light.
 

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Discussion Starter #4
Oh yeah, forgot to put that in there. I'm seeing approximately 35 degrees then.
 

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Your "knock" can be either timing-induced early ignition, pre-ignition due to a "hot spot" or other combustion chamber defect, or detonation resulting from a combination of 2 or 3.

One symptom of too much vacuum advance is "tip-in" spark knock that comes on loudly on light throttle but lessens as the throttle is opened wider. Spark knock that gets louder the harder you press the pedal is the result of high cylinder pressure combined with too much spark advance (not vacuum but mechanical) or may even not be spark advance after all, but wrist pin or piston skirt slap.

The first step should be to get rid of the knock under mechanical advance only by capping your vacuum line and adjusting your initial advance and advance curve. You can delay the onset of advance somewhat by adding just ONE heavier advance spring. Once you've address that issue you can move on to tailoring your vacuum advance (most units are adjustable via an allen wrench down the orifice) so that a higher vacuum signal is needed to move the diaphragm. Ideally, you should get a lot of vacuum advance at closed throttle (idle and deceleration) a bit at light throttle cruise, and little to none otherwise.

You may also want to check your spark plug heat range. If you're unable to tune out the knock and mention you have MSD ignition you may want to explore using a timing control to retard the timing at specific times.
 

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There was a day when I could hear the "Tip in" spark knock, but not for the last 30 years. Back in the day I drove a 1 ton Ford everyday in the field as I worked on Seismic crews. In 79 the company gave me a new Ford truck with, I believe a 400, with a 4 speed. Twas a real dog but ran good. Pinged a lot when lugged but that was it.

I do know that I have never heard spark knock/pinging at anything but low RPM. The rest of the engine makes so much noise it drowns it out.

Now I have had detonation issues in an engine and it destroyed a couple of pistons. I heard nothing while the detonation was happening but felt it when the pistons let go.
 

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As others have said, if when you “get on the gas it starts knocking loudly” it is not a vacuum advance problem as there is little, if any, vacuum available to advance the spark (whether connected to manifold or port vacuum connections). It “sounds” like you have too much advance in your timing. Clearly, if you disconnect the vacuum advance and the problem continues it sure doesn’t seem to be the cause of the problem.
Here are some thoughts: First, check the spark plugs. Are they the right temperature range (“hot” plugs are used when an engine is burning oil to keep them from fouling)? Too hot a plug will cause the engine to pre-ignite. Second, are your timing marks correct – do they “read” 0 when the engine is actually at TDC. I’ve read of front pulleys/harmonic balancers shifting on their axis. Or the pointer could be wrong. If not correct your timing is off (even if you've set it correctly). Third, are you running gasoline with a high enough octane for the engine’s compression ratio?
I certainly hope it’s not an internal problem.
Good luck. Keep us informed of your progress (and, hopefully, solution).
 

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Discussion Starter #8
Here are some thoughts: First, check the spark plugs. Are they the right temperature range (“hot” plugs are used when an engine is burning oil to keep them from fouling)? Too hot a plug will cause the engine to pre-ignite. Second, are your timing marks correct – do they “read” 0 when the engine is actually at TDC. I’ve read of front pulleys/harmonic balancers shifting on their axis. Or the pointer could be wrong. If not correct your timing is off (even if you've set it correctly). Third, are you running gasoline with a high enough octane for the engine’s compression ratio?
Thanks for the input all.....

I haven't pulled a plug in years but let me get out there and do it. I don't remember buying anything special, just the standard for that engine.
The timing marks look to be right on, I did check to see that number 1 was at the top when the distributor was pointing at that spot and the marks were aligned.
I use regular (cheap) pump gas.
As Woodchuck mentioned, might be time to get into the distributor although after reading over and over I still don't know if I want to try it on my own. Next time I'm at the junkyard maybe I'll pull one to send in for refurb.
Just annoying to me, I ran without any vacuum line hooked up for years, hooked up the manifold vacuum because I found a fitting on the old 2V manifold I have sitting around.
 

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As was mentioned....should you decide to "refurb" your distributor, contact Dan Nolan at the MustangBarn, in Harleysville Pa. He'll ask for a list of specs to include with your Distributor. He'll make it right!
Also, know for sure your balancer is indexed correctly with respect to the "0" and the timing indicator. Just because the rotor is pointing to #1 is not sufficient. The balancer rubber ring could have slipped over time.
 

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Something else to look into. Engines equipped with EGR would sometimes pull in a lot of timing quickly to improve driveability. Up to 60° BTDC could be tolerated with EGR and not knock. My dad had a 77 Granada with a 302. With the EGR hooked up the car ran fine with no issues. As soon as you disconnected the EGR, It would ping and knock uncontrollably at anything other then sitting and idling.

A lot of Ford vacuum advances are adjustable. Access is through the nipple with a Allen wrench. See if this is possible and if so, try adjusting it. Keep notes from your starting point.
 

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vac advance will only make a difference during light/part throttle. once opened up the mech adv takes over

Id have your dizzy properly recurved by Dan @Glazier Nolan
I am sure you are referring to Dan Nolan at The Mustang Barn. He can be contacted at :

Daniel Nolan
Mustang Barn & American Classics
651 Sumneytown Pike
Harleysville, PA 19438
215-723-3722
[email protected]

I just sent him my Duraspark in for a proper timing curve. Excellent communication. I cannot wait to get the dizzy back...and then some clean, dry roads for a test drive. :)
 

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I am sure you are referring to Dan Nolan at The Mustang Barn. He can be contacted at :

Daniel Nolan
Mustang Barn & American Classics
651 Sumneytown Pike
Harleysville, PA 19438
215-723-3722
[email protected]

I just sent him my Duraspark in for a proper timing curve. Excellent communication. I cannot wait to get the dizzy back...and then some clean, dry roads for a test drive. :)
I received mine back a few months ago. Have fired it and tuned per Dan’s advice. Mine is a Motocraft with an Ignitor. It sounds good but now, I‘m in the process of changing fluids. His specs were a bit different than what I expected. So, we’ll see how she performs on the road.
 

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Yes, it was a week or so for mine, too. But, it may be the time of year? Mine was just before Christmas. Initially, it was in pretty good shape. So, it was mostly the re-curve and evaluation that took the time. I'll add, in addition to the "20 questions", that Dan asks (I say this in a good way), it's important to let him know your VAC source. I run "full" manifold Vac. It gives him the complete picture, so to speak. I plan to Dyno and tune in the spring. My Last Dyno was with a 680 CFM Custom Holley XE.These WEBERS are different birds.
 
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