Slight 'Pinging' Off Idle
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Joined: Sep 2019
Posts: 85
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Slight 'Pinging' Off Idle
Do I just retard the ignition timing and dial in the carb? It's a 1970 350/350 engine and I'm using Shell 93 octane. Suggestions? And no, I'm not cutting the piston tops down. lol
Instructor
Joined: Jun 2018
Posts: 110
Likes: 3
Hello Ray
In a word....Yes
I bought a digital timing light.
It was worth the money
I had to dial back to 34 advance before vacuum at 3300 RMP to avoid pinging.
The readout really helped me fine tune it in.
Good luck
In a word....Yes
I bought a digital timing light.
It was worth the money
I had to dial back to 34 advance before vacuum at 3300 RMP to avoid pinging.
The readout really helped me fine tune it in.
Good luck
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Make sure your vacuum advance is not providing more than 10 to 12 degrees of additional advance. To see if it's the problem, simply yank the vacuum hose off of it and plug it. If the problem goes away, your vacuum advance is providing too much additional advance and must be limited. If the problem does not go away, you need to retard your initial timing.
Lars
Lars
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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try sunoco 93 as well. I had an issue with a station not using 93 in the 93 tank.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
I have an L79 (11:1 comp.) and use Shell 93. I've also bumped the timing back a hair and tuned the carb a little on the fat side. Re-adjust for summer when heat and humidity increase. Better to be safe than sorry. 
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
As stated...go through your advance curve and double check......then check how much the vacuum can is pulling overall. You may need an adjustable vac can which is available from many vendors.
My money is on the vac advance not falling off fast enough.
Is it plugged in to full manifold vacuum?
Jebby
My money is on the vac advance not falling off fast enough.
Is it plugged in to full manifold vacuum?
Jebby
Drifting
Joined: Jan 2011
Posts: 1,853
Likes: 81
From: Hamilton Virginia
I know it's not a Corvette, but wanted to share. If I use regular or midgrade in my truck, I have pinging. Once I put 93 octane in, the pinging goes away. I will be retarding the timing here soon.
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Verdad Gallardo
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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Does the truck have a performance motor or do you need the performance of the advance?
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,094
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From: Marlton NJ
If it's pinging slightly off idle,,that's probably the vac advance. Unplug it to see if the pinging goes away. You can limit the vac can to 10 degrees total with a small vac limiter plate from Lars. If that doesn't solve it you'll need to find a diff can so you can change the vac level that it pulls off at.
I had to do a lot of that sort of tuning on my 1970 LT-1 with a blue-printed 11:1 CR. With those vac mods and 32 degrees total it would run fine on 93 octane. But it would also run 30HP stronger with a different tune and about 97-99 octane.
I had to do a lot of that sort of tuning on my 1970 LT-1 with a blue-printed 11:1 CR. With those vac mods and 32 degrees total it would run fine on 93 octane. But it would also run 30HP stronger with a different tune and about 97-99 octane.
Last edited by leigh1322; Sep 29, 2019 at 05:04 PM.