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Author Topic: Spark Knock  (Read 3858 times)
sixt9x33rs
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« on: April 03, 2010, 08:18:12 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.

Thanks,
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
Ed Bertrand
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« Reply #1 on: April 03, 2010, 09:20:31 PM »

Not to hijack your thread, but where are you getting 93 octane (let alone 100)?? Here in So Cal, the highest octane we can get is 91, and they call that (laughable) "Premium"!! Forget about 100 octane unless you go with racing gas at $7.50 a gal.

Ed
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sixt9x33rs
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« Reply #2 on: April 04, 2010, 07:37:36 AM »

I am in Charlotte NC. 93 Octane is run of the mill. It is everywhere. We use to have 91 several years ago and it went up to 93 a long time ago.

Several stations in Charlotte have 100 octane but it is $6.99 a gallon. It is billed as racing gas but not hardly. If I want the real racing gas I go to nearby Gaston County (remember you are in NASCAR Country here and with NASCAR comes pure redneck) being from Charlotte I include myself in this group. There is a station right on Mecklenburg/Gaston County line that sells 110 Octane Can Am fuel for the dirt track racing boys. (Like I said pure redneck) This is where the real juice can be found. When I put that in any of my old cars they truely come to life. The problem is that it is about 20 miles away. So in the Z I will burn about 1/4 of a tank coming home. I have not been over there in awhile so I don't know what it cost a gallon now. I need to take my plastic tanks over there in my Suburban and fill those up, and fill up the Z and Vette. I know the spark knocking goes away then.

I figured you So. Cal boys would appreciate some good redneck humor.
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
JohnZ
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« Reply #3 on: April 04, 2010, 10:12:43 AM »

my timing is 10* at 900 RPM.

What does the rest of your timing map look like? When does your centrifugal advance start, and how much advance does it add at what rpm? What vacuum advance unit do you have (stamping on the bracket) and is it connected to "ported" vacuum (stock) or to full manifold vacuum?

Spark knock (detonation) is a function of ignition timing, not carburetor calibration.
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Ed Bertrand
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« Reply #4 on: April 04, 2010, 12:11:32 PM »

Man, it must be nice to still be able to get fairly good gas. I grew up in the days of Sunoco 260. At .24 cents a gallon and 102 or 103 octane if I remember correctly!

Ed
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Gramps69Z
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« Reply #5 on: April 04, 2010, 01:19:48 PM »

Man, it must be nice to still be able to get fairly good gas. I grew up in the days of Sunoco 260. At .24 cents a gallon and 102 or 103 octane if I remember correctly!

Ed



Ed, I remember gas statons having "wars" in the sixtys and gas  going for 15-18 cents a gallon and selling good gas.  I think most of the suppliers today deliver to more than one station and that's why the prices are set.
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sixt9x33rs
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« Reply #6 on: April 14, 2010, 06:04:47 AM »

my timing is 10* at 900 RPM.

What does the rest of your timing map look like? When does your centrifugal advance start, and how much advance does it add at what rpm? What vacuum advance unit do you have (stamping on the bracket) and is it connected to "ported" vacuum (stock) or to full manifold vacuum?

Spark knock (detonation) is a function of ignition timing, not carburetor calibration.
John the stamping on my vacuum advance is B28
I don't have an adjustable light so I can not answer your other questions. Any way to do it with just a standard light?
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
L78 steve
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« Reply #7 on: April 14, 2010, 12:40:41 PM »

Install a timing tape on your balancer. It's very important to know what you are dealing with as far as timing. All 3 stages of timing, Initial,centrifugal and vacuum. The only other thing I can think of that can cause a knock that has not been mentioned is a stuck closed heat riser valve. This causes the intake manifold to become very hot, super heating the intake charge.
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69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
rich69rs
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« Reply #8 on: April 14, 2010, 01:28:58 PM »

Install a timing tape on your balancer. It's very important to know what you are dealing with as far as timing. All 3 stages of timing, Initial,centrifugal and vacuum. The only other thing I can think of that can cause a knock that has not been mentioned is a stuck closed heat riser valve. This causes the intake manifold to become very hot, super heating the intake charge.

As a follow up to Steve's good suggestions,

Timing tape or use a set back timing light which can read the full amount of timing.

As far as the heat riser valves, I removed mine (from my Camaro and Chevelle) and installed spacers in their place which are readily available from the aftermarket.  

Back in the day, the heat riser valves were problematic enough.  Today, it is tough to find replacements that won't bind up after little use.  By not having them, the preheat of the intake manifold is compromised, but it hasn't been a problem on either my 69 RS or my 66 Chevelle.  Once the engine warms the heat rise valve should be open and is just a restriction in the exhaust pipes.

Just my two cents.

Richard

Good luck.
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Richard Thomas
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sixt9x33rs
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« Reply #9 on: April 15, 2010, 05:40:31 AM »

Install a timing tape on your balancer. It's very important to know what you are dealing with as far as timing. All 3 stages of timing, Initial,centrifugal and vacuum. The only other thing I can think of that can cause a knock that has not been mentioned is a stuck closed heat riser valve. This causes the intake manifold to become very hot, super heating the intake charge.

I will look into the tape or just buy an adjustable light. The tape and light do the samething right?
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
sixt9x33rs
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« Reply #10 on: April 15, 2010, 05:42:08 AM »

Install a timing tape on your balancer. It's very important to know what you are dealing with as far as timing. All 3 stages of timing, Initial,centrifugal and vacuum. The only other thing I can think of that can cause a knock that has not been mentioned is a stuck closed heat riser valve. This causes the intake manifold to become very hot, super heating the intake charge.

Great point. When I put the car back together, everyone was telling me not to put that valve back in but I was determined to put the car back together as it was when new. I will check that and see if it is closed when it should be open.

Thanks

As a follow up to Steve's good suggestions,

Timing tape or use a set back timing light which can read the full amount of timing.

As far as the heat riser valves, I removed mine (from my Camaro and Chevelle) and installed spacers in their place which are readily available from the aftermarket. 

Back in the day, the heat riser valves were problematic enough.  Today, it is tough to find replacements that won't bind up after little use.  By not having them, the preheat of the intake manifold is compromised, but it hasn't been a problem on either my 69 RS or my 66 Chevelle.  Once the engine warms the heat rise valve should be open and is just a restriction in the exhaust pipes.

Just my two cents.

Richard

Good luck.
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
JohnZ
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« Reply #11 on: April 15, 2010, 11:43:51 AM »

I will look into the tape or just buy an adjustable light. The tape and light do the samething right?

A dial-back timing light eliminates the need for timing tape installation and inaccuracy, and you can use it on any car; really simplifies "mapping" your advance curve. I've had an Actron CP-7519 for many years (about $70.00), and it works great.
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« Reply #12 on: April 15, 2010, 09:19:45 PM »

Has anyone done Johns vacuum setup without doing any other changes. If so did it work or did you have to do some other changes or did you have to do some re-timing on the engine. I do not have a timing light and do not want to get ahead of myself with the vacuum change if I also need to do timing adjustments.. Thanks ,
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L78 steve
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« Reply #13 on: April 15, 2010, 10:00:25 PM »

Has anyone done Johns vacuum setup without doing any other changes. If so did it work or did you have to do some other changes or did you have to do some re-timing on the engine. I do not have a timing light and do not want to get ahead of myself with the vacuum change if I also need to do timing adjustments.. Thanks ,

The vacuum change to a NON-ported source is important for best idle,drivability and economy. But is not your problem. If you are hearing ping at hard throttle the vacuum advance is not the cause. Because it is not a factor at low vac. Ping at hard throttle is initial timing and centrifugal advance totaled up too high,or some other issue. You must get a light and check your total with the Vac. can disconnected. It should be no more then 36*. Once you get this checked and or corrected  then see if you still hear any spark knock. A light ping at light throttle I don't worry about, but knock at hard throttle is not good.
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69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
sixt9x33rs
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« Reply #14 on: April 16, 2010, 06:32:54 AM »

Has anyone done Johns vacuum setup without doing any other changes. If so did it work or did you have to do some other changes or did you have to do some re-timing on the engine. I do not have a timing light and do not want to get ahead of myself with the vacuum change if I also need to do timing adjustments.. Thanks ,

The vacuum change to a NON-ported source is important for best idle,drivability and economy. But is not your problem. If you are hearing ping at hard throttle the vacuum advance is not the cause. Because it is not a factor at low vac. Ping at hard throttle is initial timing and centrifugal advance totaled up too high,or some other issue. You must get a light and check your total with the Vac. can disconnected. It should be no more then 36*. Once you get this checked and or corrected  then see if you still hear any spark knock. A light ping at light throttle I don't worry about, but knock at hard throttle is not good.

Your comment about light ping at light throttle is interesting. My spark knock I would classify as a light ping at mild to aggressive acceleration. I don't have a hard knock at all.

I am still going to buy the adjustable light and map my timing. I need to do this for all my cars.
Thanks
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
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.
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69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
Stingr69
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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.

-Mark.
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sixt9x33rs
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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.

Thanks

Lawrence
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
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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.

Thanks,

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.
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Gary

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