351 with Eddy 4-v. Put in t new Dizzy and set to maximum vacuum, but lots of pinging.
Set it to 10 BTDC (factory) and I get pinging, but not under "load" (heavy acceleration) Only at a "mid" acceleration, as when holding current speed on a hill. so I have set it to 8 BTDC ( but have not had a chance to try it).
This is using 89 octane ...
Thoughts?

 

Too much vacuum advance. Check to see if yours is adjustable by sliding a very small Allen wrench into the vacuum advance port. (I don't remember what size it takes.) If yours is adjustable turn it 1 turn counter-clockwise to raise the point the advance comes in by ~1" of vacuum. Keep doing that until the pinging stops.

It is possible that you have too much advance in the mechanical part of the dizzy. But, you said it doesn't ping under hard acceleration, so probably not. Given that, you have to dial back the vacuum advance, as above.

 

Try 3/32" or 2.5mm Allen

 

Did the truck originally have EGR? One purpose of the EGR system is to slow down combustion during part throttle to reduce NOX formation, but it also allows more timing advance under those same conditions.

If running a distributor calibrated for EGR, but with the system disabled, you are very likely to get pinging at part throttle like you've described.

 

1 turn of the dizzy advance as Gary suggested, and no more pinging....
Thanks again to Gary-the-go-to-reference!

 

That's a pretty small change, so you were right on the edge if it fixed it. Hopefully that's all it took.

 

I hope so too, as mentioned, it was only pinging at a mid acceleration as I=when holding speed on a long minor grade, More gas, it would go away, so it seems fine right now....

 

More gas means less vacuum which means less advance, thereby killing the ping.

 

Then why is there no vacuum at Idle?

 

Reamer, are you measuring vacuum at the distributor line at an idle? If so and there's no vacuum, you're probably hooked up to ported vacuum. Trace the vacuum line- is it hooked up to a port on the carburetor ABOVE the throttle plates?

 

Just out of curiosity, when you adjust the vacuum advance canister by way of an allen wrench, are there stops in the thing as to prevent the adjustment screw from coming all the way out?

 

The adjustment screw can come all the way out (counterclockwise), in my experience. And if it does, it can be a problem if the screw doesn't thread back in anymore 😠.

 

its an Eddy 4-v and the dizzy has no vac at idle, It is hooked to the port on the right (when you are sitting in the drivers seat).

 

You don't want to have vacuum to your dizzy's advance at idle. If you do you are likely to have surging when you drop the tranny in gear.

 

Hi Gary
My Dizzzy is hooked to one on the left (in the photo) "3/16" Timed Vacuum Port"
This is the correct spot? (but I have no emissions, EGR either)