How do I get rid of "spark knock" - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mlo714 · 01-22-2014, 09:44 PM

I finally got my truck running a 7 out of 10. After a fresh carb rebuild, new HEI dist, new spark plugs. I run premium gas all the time. When I get on the gas it sounds like the the motor is going to fall apart. Just in conversation people tell me "that's a timing issue". How do I fix this? can I just advance the dist or retard?

CST10 · 01-22-2014, 09:49 PM

You need to check the timing with a light to make sure it's on spec. With vacuum advanced disconnected first for initial setting. Then check with vacuum advance connected. I'm assuming you have a vacuum advance on it. Don't know what your engine is to give much more info.

hugger6933 · 01-22-2014, 09:52 PM

Spark Knock or "preignition" or if you can if you can remember the early 80's the term "labor knock" was also thrown about. those conditions all all from timing that is to high, retard the timing a little bit and it should all clear right up. Do you have the timing set with a light, or did you just set it by ear? Or static time when building [or working on] the motor just to get it going and then it was so close you wanted to try it. If you put a light on it did you set it at an idle or an all in type thing at a certain rpm? Jim
?

mlo714 · 01-22-2014, 09:57 PM

Its a '72 307 with a 2bbl carb. I am very new to doing this on my own. I havnt checked it with a light yet. I know the difference between advance and retard but that's about it. Ill check it this sat and try to retard it a little and see if it goes away. I put new plugs in it and didn't gap them. It was having the knock before the new plugs as well.

mlo714 · 01-22-2014, 09:59 PM

If I stomp on the gas it wont do it....its only under load at light-mid throttle.

turp mcspray · 01-23-2014, 12:01 PM

Quote:

Originally Posted by mlo714

If I stomp on the gas it wont do it....its only under load at light-mid throttle.

This sounds to me like a vacuum advance issue. Unhook the advance, and then go for a drive. A lot of distributors have lots of vacuum advance (like 24 degrees) to make up for a really weak timing curve. If you set the initial timing for more advance than stock, the vacuum can may push it too far during light throttle, high vacuum, driving. If this is the case, you simply need to limit the vacuum advance. About 10 degrees is a good number for a performace type of timing curve.

DT1 · 01-23-2014, 02:14 PM

Quote:

Originally Posted by turp mcspray

This sounds to me like a vacuum advance issue. Unhook the advance, and then go for a drive. A lot of distributors have lots of vacuum advance (like 24 degrees) to make up for a really weak timing curve. If you set the initial timing for more advance than stock, the vacuum can may push it too far during light throttle, high vacuum, driving. If this is the case, you simply need to limit the vacuum advance. About 10 degrees is a good number for a performace type of timing curve.

Agreed, if the knock occurs just at low speed/part throttle, it's more than likely a vacuum advance issue. BTW...if it's a stock 307 with 2BBL you only need to run regular gas. You are just wasting your cash with premium. It will do NOTHING to improve economy or performance.

You might find this interesting...
http://www.consumer.ftc.gov/articles...ctane-gasoline

71 super · 01-22-2014, 11:00 PM

Pull timing out and also better fuel, colder plugs all will help get spark knock out

70blackfish · 01-23-2014, 12:57 AM

its really bad for a motor, better gas. and check engine temp.

Ridgeclimber · 01-23-2014, 01:40 AM

Check the timing with a light or you can also use a vacuum gauge. With the idle turned up to about 1000 rpm, advance or retard the timing until you get the highest vacuum reading. Then retard the timing until the vacuum gauge drops 1 inch of vacuum. Then turn the idle back down. If it still pings it also could be a lean air fuel condition. What did you do to the carb?

70LonghornCST · 01-23-2014, 01:59 AM

Like others have posted, retard the timing and check the fuel/air mixture needles on the carb...also verify the timing with a timing light.

**Grumpy old man** · 01-23-2014, 06:29 AM

Go back and start from the beginning ,

pull the plugs and gap them
set the timing with a light
a fresh carb rebuild does not mean it is correct just close ,many guys can tune a carb by "ear" I would imagine these steps should easily fix your issue .

*Fitz* · 01-23-2014, 02:54 PM

Quote:

Originally Posted by mlo714

I finally got my truck running a 7 out of 10. After a fresh carb rebuild, new HEI dist, new spark plugs. I run premium gas all the time. When I get on the gas it sounds like the the motor is going to fall apart. Just in conversation people tell me "that's a timing issue". How do I fix this? can I just advance the dist or retard?

Retard the timing.

01-22-2014, 09:44 PM	#1
mlo714 Registered User Join Date: Jul 2013 Location: Myrtle Beach SC Posts: 18	How do I get rid of "spark knock" I finally got my truck running a 7 out of 10. After a fresh carb rebuild, new HEI dist, new spark plugs. I run premium gas all the time. When I get on the gas it sounds like the the motor is going to fall apart. Just in conversation people tell me "that's a timing issue". How do I fix this? can I just advance the dist or retard?

01-22-2014, 09:49 PM	#2
CST10 Registered User Join Date: Sep 2013 Location: Gonzales, La Posts: 1,441	Re: How do I get rid of "spark knock" You need to check the timing with a light to make sure it's on spec. With vacuum advanced disconnected first for initial setting. Then check with vacuum advance connected. I'm assuming you have a vacuum advance on it. Don't know what your engine is to give much more info. __________________ MyToys: Goldilocks the "Ol School Survivor" 1968 C10, SWB Stepside, 08/15 TOTM, 250 CI 6 cylinder, 3 on the tree, 3.73 rear, 3/5 static drop, 23,500 original miles. Samson the 1970 CST10, LWB, 462Ci, Turbo 350 tranny, 3.08 rear gear, PB, PS, A/C, AM/FM, 2/4 Drop. Brutus the 1998 Camaro Z28, 33,500 original miles, LS1, 519 RWHP/497 RWTQ. Member of the Louisiana Classic Truck Club, LCTC Member of the Louisiana C10 Club Member of the Baton Rouge Drifters Car Club

01-22-2014, 09:52 PM	#3
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,280	Re: How do I get rid of "spark knock" Spark Knock or "preignition" or if you can if you can remember the early 80's the term "labor knock" was also thrown about. those conditions all all from timing that is to high, retard the timing a little bit and it should all clear right up. Do you have the timing set with a light, or did you just set it by ear? Or static time when building [or working on] the motor just to get it going and then it was so close you wanted to try it. If you put a light on it did you set it at an idle or an all in type thing at a certain rpm? Jim ?

01-22-2014, 09:57 PM	#4
mlo714 Registered User Join Date: Jul 2013 Location: Myrtle Beach SC Posts: 18	Re: How do I get rid of "spark knock" Its a '72 307 with a 2bbl carb. I am very new to doing this on my own. I havnt checked it with a light yet. I know the difference between advance and retard but that's about it. Ill check it this sat and try to retard it a little and see if it goes away. I put new plugs in it and didn't gap them. It was having the knock before the new plugs as well.

01-22-2014, 09:59 PM	#5
mlo714 Registered User Join Date: Jul 2013 Location: Myrtle Beach SC Posts: 18	Re: How do I get rid of "spark knock" If I stomp on the gas it wont do it....its only under load at light-mid throttle.

01-22-2014, 11:00 PM	#8
71 super Registered User Join Date: Sep 2005 Location: Canton North carolina Posts: 3,080	Re: How do I get rid of "spark knock" Pull timing out and also better fuel, colder plugs all will help get spark knock out __________________ 67 blue step side- bb 68 gold and white swb cst anniversary 68 custom swb hot rod Ls swap 69 swb cst 6 cylinder/ overdrive 69 black/black cst bb swb 70 orange and white cst Canada built truck swb bb 71 black and white super swb bb 71 red and white super swb 72 green and white super swb 4x4 62 nova wagon 400 series Ls swapped 68 Camaro 327/4 speed- 1 owner, original paint 66 Volkswagen bettle 69 auto stick Volkswagen Beetle

01-23-2014, 12:57 AM	#9
70blackfish Registered User Join Date: Oct 2012 Location: Newhall CA Posts: 1,195	Re: How do I get rid of "spark knock" its really bad for a motor, better gas. and check engine temp. __________________ 69 SWB 780hp Hellcat powered, manual 6 speed, currie 9

01-23-2014, 01:40 AM	#10
Ridgeclimber Registered User Join Date: Jul 2012 Location: Maple Ridge. B.C. Posts: 145	Re: How do I get rid of "spark knock" Check the timing with a light or you can also use a vacuum gauge. With the idle turned up to about 1000 rpm, advance or retard the timing until you get the highest vacuum reading. Then retard the timing until the vacuum gauge drops 1 inch of vacuum. Then turn the idle back down. If it still pings it also could be a lean air fuel condition. What did you do to the carb?

01-23-2014, 01:59 AM	#11
70LonghornCST Moderator Join Date: Jun 2008 Location: Modesto, CA Posts: 5,775	Re: How do I get rid of "spark knock" Like others have posted, retard the timing and check the fuel/air mixture needles on the carb...also verify the timing with a timing light. __________________ 2018 Chevy Crew Cab 2006 Impala SS 1965 Plymouth Sport Fury 1970 Chevy Longhorn Bucket Seats Shoulder Belts Front Tow Hooks Factory Air Factory Speedwarning, Tach & Vaccum Factory Tilt CST Package AM/FM Radio Bumper Guards Richard 70 Longhorn CST Build Adding an AM/FM Decal

01-23-2014, 06:29 AM	#12
Grumpy old man Senior Member Join Date: Dec 2013 Location: Gods country East,Tn Posts: 8,545	Re: How do I get rid of "spark knock" Go back and start from the beginning , pull the plugs and gap them set the timing with a light a fresh carb rebuild does not mean it is correct just close ,many guys can tune a carb by "ear" I would imagine these steps should easily fix your issue .



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