i have tried almost everything to stop the pinging.this is a 78 350 L48.new plugs,wires,distr.cap,rotor,vacume hoses,carb is rebuilt,rad.seems to be good ,i have used 94 octane etc and it still pings when up to temp.It was suggestd i try installng a distr.recurve kit (new springs & weights)has anyone tried this and did it help.

 

There is a good chance you have a fairly large carbon buildup in your heads. This carbon will get red hot and cause pre-ignition even on premium gas with a fairly low compression engine.
Back in the day, we used to take a quart of ATF, head out into the country and pull off to the side of some deserted road. Then with the car running and the top of the Air cleaner off, slowly pour it into the carb. Reving the engine up as you do to keep the motor running. Smoke will pour out of your exhaust and send up a plume for miles. :D That's why you go out of town away from anyone that can report you to the authorities.
Some people take a mixture of half water and half ATF and using it. You have to shake the mixture to keep it mixed up as you pour it in the carb.
There is a product called Sea-Foam that is designed to do the same job or burning off the carbon.
This is a true old time trick to stop the engine from clattering, we used to do it about twice a year back in the 50's and 60's and I never had a problem with any engine we did this on.
Good Luck!

 

Could be back pressure from the catalytic converter if you still have one. I had a 80 Formula start pinging due to that. Felt like a new engine once I had it replaced.

 

Have you checked the timing?

Is the manifold too hot?
If so, it could be a stuck/faulty heat riser (between the passenger exhaust manifold and the engine pipe).

If it's none of the above, maybe an insulating spacer between the carb and manifold would help.

 

I believe you may have a timing issue. First check your vacuum advance to see if it works. Then check your total mechanical advance by doing the following:
1. remove the springs from the advance fly-weights and reassemble the distributor.
2. Disconnect and plug the vacuum advance line
3. Using a dialback timing light start the engine and increase speed until you can dial in your maximum advance, it should be no more than about 36 degrees. With the springs off this should occur around 1200 rpm. Make sure it's maxed out by revving the engine a little.
4. If it is more than 36, adjust the distributor until you are at 36 btdc.
5. Re-install the springs, vacuum line, and road test. If it still pings back off the timing a couple degrees at a time until it stops, but you shouldn't have to go far.
6. Still pings at anything less than about 30 could mean other problems, all good suggestions from other posts above.

Lars has an excellent article on vacuum control units on the faq site, here is a link to one on vacuum contols: http://www.corvettefaq.com/redir.asp?site=570

Here is another excellent Lars article on ignition timing: http://www.corvettefaq.com/redir.asp?site=26

And still another on setting distributor curve: http://www.corvettefaq.com/redir.asp?site=425

And by the way, welcome to the forum. I am sure you will find plenty of help here! :cheers:


[Modified by Big Fish, 11:09 PM 1/19/2003]


[Modified by Big Fish, 11:17 PM 1/19/2003]

 

His '78 should have an HEI setup - you can't removed the springs without causing an overly advanced condition. He needs to check the timing with everything but vacuum advance hooked up.

 

You are correct, it will cause an advanced condition, but not more advanced then the distributor would do on it's own at high rpm with the springs connected. Sure, the engine will buck a little starting it, but this condition is only for as much time as it takes to dial in the centifugal advance. In my opinion, it's easier to check the full advance at lower rpms. The safest way would be to remove the distributor and put in on a distributor machine to dial in the advance, but how many people have one of those at their disposal?

 

Actually it will advance it more than the engine would ever see with the springs connected. Pop the cap off your HEI distributor, remove the springs and see for yourself.

Also, to quote Lars' timing tech article:

 

whoops, I guess I missed that part. Same procedure would work with the softest springs however. I just hope this can solve the guy's problem. :cheers:

 

I feel your pain. I feel like i tried it all on my '69, timing, vaccum, atf down the carb, water down the carb, carb rebuilt, new distributor, octane boost. I finally gave up on trying to resurrect the original 180,000+ mile drive train and am now in the process of building a replacement engine. i chased the pinging in my car for over 3 months, ended up changing alot of stuff, and never did figure it out. The pinging is actually what moved the engine transplant up 6 months, cause i was sick and tired of throwing time and money at it with no change. that probably doesnt help, but you're not alone. good luck, let us know what you find.