Engine 225 Odd Fire Timing Issue

[Kruzkraft]

70 CJ5 stock original 225 with 56k on it. I rebuilt the 2g and converted to HEI with the adjustable vac adv. Is running great, good clean idle, nice steady acceleration. The problem is, best idle quality and 21inches of manifold vacuum requires 14 degrees BTDC of base timing with no vac or mechanical advance. The engine will pull steady through the RPM range, but I hear it ping going up hills while under load. I backed out the vacuum advance to zero and retarded the timing to 10 degrees initial. The idle gets rough and vacuum drops below 18inches. Drives good, but still pings.
I thought I had better put this out there for you smart guys before I started down the rabbit hole of trying to recurve the distributor.

 

[Manic Mechanic]

hows your gas. try running premium or octane booster with ur old settings and see if the ping goes away

Sent from my E6810 using Tapatalk

 

[Kruzkraft]

Thanks, I’m using 92 ethanol free. When I pulled the carb I found that this engine uses the primitive EGR principle of routing the exhaust gas up from the heads and under the carb. The carb kit only had two choices of flange gaskets, maybe I chose the wrong one.

 

[Kruzkraft]

When we rebuilt or modified sb chevys we would use the intake gaskets that had a block off provision to isolate the exhaust gas from the intake. This would help to eliminate leaks. I’m wondering if the 225 has any inherent problems associated with the intake/head design that I need to investigate.

 

[caveman]

Something that helps my rig is lead additive. Those older rigs were designed to have lead in the gas.

 

[Belizean]

Something that helps my rig is lead additive. Those older rigs were designed to have lead in the gas.

Just like the small general aviation engines

 

[BrockGrimes]

What fuel octane did you run before the upgrade? Did it ping before the HEI?