Knocking and Pinging

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eForce
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Knocking and Pinging

Unread post by eForce » Tue Apr 18, 2017 5:19 pm

Hi guys. Finished replacing the head on the drivers side. Got the motor built and reinstalled. Runs WAY better than before. As long as it's cold. The problem is, once it warms up AND I'm at idle in drive, it knocks and pings like crazy. Once I give it a little gas, it runs great again.

Any ideas? I've played with the timing, carbs and checked for vacuum leaks.

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terribleted
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Re: Knocking and Pinging

Unread post by terribleted » Tue Apr 18, 2017 5:30 pm

play with them some more and also check idle speed. This symptom in a powerglide is usually timing and rpm related
Last edited by terribleted on Tue Apr 18, 2017 5:40 pm, edited 1 time in total.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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Located in Snellville, Georgia

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eForce
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Re: Knocking and Pinging

Unread post by eForce » Tue Apr 18, 2017 5:36 pm

agreed but why would it run so great with no knocks when it's cold?

Jerry Whitt
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Re: Knocking and Pinging

Unread post by Jerry Whitt » Tue Apr 18, 2017 6:11 pm

What is different when cold?

The most common difference is the chokes are nearly closed and the fast idle is holding a much higher idle speed. The means there is a much richer mixture when cold. The rich mixture will hold off the pinging or knocking.

You noted that when accelerated, runs better. Sounds like the hose to the vacuum advance is hooked up to intake manifold vacuum and the choke pull off is hooked to the spark port. Recheck.

Timing is critical, of course, and an error in setting or a bad harmonic balancer could cause these symptoms.
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66vairguy
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Re: Knocking and Pinging

Unread post by 66vairguy » Wed Apr 19, 2017 9:44 am

Back to basics. Check the static timing at the specified RPM and make sure the vacuum advance is disconnected until after you set the timing.

Another mistake folks make is they hook the distributor vacuum advance to the wrong carburetor port so the vacuum advance goes full on (should be little or no vacuum at idle using the correct port).

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eForce
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Re: Knocking and Pinging

Unread post by eForce » Sun Apr 23, 2017 8:05 am

ok so I set the timing properly. It was out a bit but not much. 2ndly I adjusted my chokes. Still knocked when it warmed up. My vacuum advance is hooked up to the top port so I tested it and my vacuum was at 9. I then tested the bottom port and that was 10 so I moved the vacuum advance to that port and that seemed to resolve it. Is that the right port?

Now it stumbles a bit intermittently but I'm certain that's my chokes.

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Re: Knocking and Pinging

Unread post by 66vairguy » Sun Apr 23, 2017 8:35 am

There are two vacuum ports near the base. The horizontal tube port goes to the choke pull off module. The vertical tube port goes to the distributor advance canister. Since BOTH carburetors have these two port and only ONE vacuum hose goes to the distributor, the other carburetor should have a rubber cap on the unused vertical tube port. If the engine is properly tuned there should be little or no vacuum at the vertical tube port at idle, but vacuum as the throttle is opened. When the carburetors are at fast idle (choke on) the throttle plate is open enough so you will see vacuum at the vertical tube port. You will ALWAYS see vacuum at the horizontal tube port to the choke pull off when the engine runs.

This is based on a properly tuned engine with no issues. Have you balanced the two carburetors at idle with a tool like a Uni-Sync?

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Re: Knocking and Pinging

Unread post by bbodie52 » Sun Apr 23, 2017 9:05 am

:goodpost: Here are a couple of illustrations that might help by supporting the above explanation...

Image

Image
A UniSyn gauge measure air flow volume through the throat of each carburetor. It is an effective method of synchronizing multiple carburetors, and can help to ensure even matched airflow at idle and at open throttle. It is one aspect of the engine tuning process.

You want a balanced pair of carburetors that are both clean and equal, and balanced for airflow at idle and at part throttle. A Unisyn air flow gauge is an inexpensive tool that helps to accomplish this. The following Corvair Forum link will provide you with a description of the function and use of a Unisyn gauge:
:link:viewtopic.php?f=55&t=5922&p=40585&hilit=air+flow#p40585
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64powerglide
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Re: Knocking and Pinging

Unread post by 64powerglide » Sun Apr 23, 2017 10:08 am

I have yet to see what your timing light says about your timing, you say you set it properly which is what when the engine is hot????? It should be 12 or 13 BTDC at 500RPM in drive with the vacuum hose off & plugged. If you have everything set right & you still get knocking & pinging your low band in the trans might need to be set. I had my 64 low band adjusted last year by a good Corvair trans guy & now it doesn't want to stall when I come to a stop.
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terribleted
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Re: Knocking and Pinging

Unread post by terribleted » Sun Apr 23, 2017 10:55 am

You say 9-10 " of HG at idle is your vacuum reading? That is way low. Vacuum at idle in a good engine should be 17-21". Causes might be a vacuum leak (do the balance tube hoses seal on both sides? Is the extra vacuum port on the left carb blocked off. Do the carbs use mounting gasket, spacer, gasket on both sides? Low compression can cause low vacuum. Improper valve adjustment can cause low vacuum and quite noisy pinging type sounds. I would make sure I have no vacuum leaks and then I would re-adjust the valves. It is very possible you have had a lifter or lifters pump up that are now holding the valves slightly open leaking compression. When they are like this when you accelerate the engine the symptom can smooth out since the time the leaking is happening is minimized. Have you tested compression? You would likely see this issue on a compression test.

Here is a link I found to vacuum testing of engines http://www.gregsengine.com/using-a-vacuum-gauge.html
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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eForce
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Re: Knocking and Pinging

Unread post by eForce » Sun Apr 23, 2017 3:48 pm

Yes, I looked that up and put the vacuum advance back on the vertical port. I got vacuum up to 11 with curb idle. Compression is 150. Timing is at 10 deg. If I go more...the knocking comes back.

I did replace the wires because I seemed to have a weak spark. That helped out quite a bit but now I've messed up my carbs and needs to be synced again.

Problem MIGHT be solved. The carbs were rebuilt a couple years ago. but the drivers side seems to be a very weak squirt compared to the passenger side. I have the chokes completely disconnected right now.

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Re: Knocking and Pinging

Unread post by 64powerglide » Sun Apr 23, 2017 4:19 pm

I'm running my 64 110 at 14 BTDC, I had it at 16 but was getting spark knock at 60 to 70 MPH so I backed it off to 14. I'm running 87 octane fuel. If you can't get it to run good when it's over 10 degrees advanced something else is wrong. :my02:
64Powerglide, Jeff Phillips

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terribleted
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Re: Knocking and Pinging

Unread post by terribleted » Sun Apr 23, 2017 5:27 pm

The accelerating fuel squirt is not particularly relevant to your issue. If one carb draws way more air than the other at idle that is very possibly related. You may have a plugged up carb. So let me get this right you rebuilt the engine and did not go thru the carbs? Go thru both carb immediately, reset all tolerances, make sure all passages are clear and ensure both draw evenly at idle and are balanced to each other. See how the car is at that point. If still doing similar stuff I would doing a running valve adjustment, adjusting to 3/8- 1 of a turn of pre-load if the lifters will take 1 turn in without misfire. Your vacuum readings are still 30% or more low Indicating low compression, big vacuum leak, or bad valve adjustment (perhaps a dead carb could make similar vacuum readings? A dead carb can certainly make the car knock and ping under load.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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Located in Snellville, Georgia

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