Sounds more like it is running too warm. After 30-45 minutes everything will be good and warm.That is when the pinging starts right?
Make sure the cooling system is up to snuff, clean the fins of the radiator, also look inside it could be pretty well plugged by deposits, you may need to drain the radiator to see the plugged tubes from the inside.
You could try a chemical flush on the system.Also check the thermostatic fan
operation. It should lock in and pull air at a certain temp.When it is at full warm up,check to see if it is pulling air aggressively, or if it is just freewheeling.
You may need to watch it while having it warmed up, in park while setting it on a fast idle.Give it a few minutes to get real warm, then You will be able to hear when it starts to pull air.If it never gets to the point where it locks down and pulls air, it probably is defective.Also watch the rad temp with an infra red temp gun. Check it at the top inlet of the rad as it runs.If it hits 235-240 and you get no fan action, then either the rad isn't throwing enough heat or the fan aint working.
Also I would check the full amount of ignition timing advance, maybe you can limit the vacuum amount or mechanical amount to help the situation.
Chances are the vacuum is pulling a bunch and would be the place to start.
Maybe you can limit that to help, but I would address the cooling system first to be sure.
Also, if the engine has carbon build up on the piston tops that will increase the compression and cause a problem.You can rig up a seafoam drip to help clean the carbon from the tops, and that may help a lot. Plus it is pretty easy and inexpensive, and could solve the problem.
If it has an EGR valve check its operation as well. If it fails to work it can also cause a spark knock when warm. Recirculated exhaust gas introduced into the combustion chamber actually slows the burn keeping the combustion chamber cooler at the top, which helps to prevent pinging.Manufacturers install EGR to help keep Oxides of Nitrogen in check as it cools the combustion chamber temps.
I don't think the issue is only one thing. My guess is a couple of things in combination.
I recommend checking and trying the aforementioned items before " digging in" to any specific thing, carb - heads whatever,as it could be that simple.
If I were to guess, I would say radiator is borderline, and or engine has excessive carbon.
Keep us posted.
Fact is stranger than Fiction
Last edited by LATECH; 06-10-2012 at 07:43 AM.