ping at high speed or foot to the floor

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k3522

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I have had a pretty good ping at higher RPM foot to the floor and hitting it to the floor in general. I checked timing with the vacuum pluggged off and was still 18*idle, 34*@ 3200rpm (which is what my FBO distributor was curved to) but for kicks after checking the timing I hooked the vacuum up and it goes to 49* @ 3200rpm which may not mean anything because there is no load.

I took the FBO distributor out and put my old Mopar curve distributor (7*, 35*) in and the same ping happened. I then did a full turn clockwise on the vacuum advance and it runs great.

I want to put the FBO distributor back in because it idles way better. Can I, should I do the same adjustment to the vacuum advance?

I know it may not be the correct fix but I am not willing to buy a bigger carb.

I just last week put in a new Edelbrock Thunder series AVS 650 carb last week thinking that would cure the ping. It made the car run way better but did not effect the ping (detonation).

I just want to drive it without hurting it. I don't need all out performance.
 
Your vacuum advance should not being adding advance at idle or WOT, it should only add timing under steady state light load crusing and 49 degrees under those conditions is not too much. If it is adding timing at idle then you have it connected to the wrong port. It should be connected to the "timed port" on the carb.

Typically if you have to much or to much to soon you will get the pinging at steady state part throttle or just as you get on the gas from a steady state condition but the pinging will stop as your manifold vacuum drops close to zero at WOT. If disconnecting the vacuum advance cures the problem then adjusting the preload in the pot is the thing to do. However, if it's still there with the vacuum advance disconnected then the mechanical advance is coming in to fast and you need stiffer springs.

If you are getting pinging at WOT then you have to much timing and/or compression for the fuel being used.
 
As said above - try reducing the FBO dizzy total mechanical timing back to 32* and reduce the vacuum to its minimum affect (screw all the way in or out??). try highest octane pump gas you can buy.
Carb size will not affect what you have as an issue.
 
At WOT vacuum advance is out of the picture, or should be. Over 3200 RPM, the distributors mechanical advance should be all the way in. I would leave the FBO distributor in, and reduce the total timing a few degrees, say 15 idle, 31 total. It sounds like 34 is a bit much for your compression and fuel grade. You are running a fresh tank of pump premium right?
 
Can you limit the total in the distributor about 4 degrees from what it has, this will allow you to keep more initial timing for off idle responce.

Also you will see some vacuam to the advance even at WOT. but as mentioned it needs to be connected to ported vac. and can be limited in total advance as well.
 
Thanks for the advice. I have tried the "timed" passenger port and the "mainold vacuum" driver side front port and they both ping. I am going to back the initial plus mechanical down from 34* to 31*. If I get no ping in a test run with the vacuum advance disconnected I will try with it connected and if I get a ping I can always turn the canister down a half a turn. Also, I am running fresh gas and a new fuel filter.
 
djwhog said:
Also you will see some vacuam to the advance even at WOT. but as mentioned it needs to be connected to ported vac. and can be limited in total advance as well.
Click to expand...


You shouldn't see any additional timing from the vacuum advance at WOT. If you have much more than 1-2"Hg of manifold vacuum at WOT your carb is way undersize and is seriously restricting the engine (for max performance you would shoot for no more than 1/2" Hg). Stock setting on a vaccum advance is 5-7" Hg, don't think you could adjust one down to the 1-2" range.
 
It amazes me why you would post this issue here, you trusted us to curve it for you why haven't you picked up the phone and called us?

If it's detonating still then we need to find out why.

Let's get this issue resolved correctly and quit taking guesses off the internet.
 
I'm with Don on this one for several reasons.

After all, you did give him ALL the engine details right? Then a simple adjustment with a (More likely a phone call with Don &) min. or 2 will be time well spent.
(No time...well.....(just) spent)
 
I have ran a couple tanks of gas, increased the AVS door spring tension and the ping is gone. Put the vacuum canister back to original setting and connected the vacuum to the constant side and still no ping. I am now going to move the timing back up from 14* to as near to 18* as possible. Looks like I got it solved, thanks to everyones help. "A bodies only" rules.
 
Between this discussion and the current thread on MSD v HEI, progress is being made.
On my part anyway.
Can’t and shouldn’t speak for others. I’m glad for honest questions and helpful answers.
If the FBO system lives up to advertisements, I may get a box, coil and cap just for kicks.
The price very reasonable. I think “Don” indicates on his web site that he is doing it for the love of Mopars and not the love of money so it might even be classified as a “good cause.”
More ignition energy should translates to better burn and better mileage, right?
The car I would put them in is already getting 23mpg.
Sounds like a win-win.


It’s a good thing Mopars are so reliable. I don’t have time to work on it right now.
But some day maybe.

Another thing is that I get knock under hard acceleration. (So I don’t do that)
That is why I decided to read this post in the first place.
But that is my problem.
I will have to find time to fiddle with my carb porting and distributor to work that one out regardless. (Qjet)
Cheap gas doesn’t help either.
 
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