Total ignition timing.

[Curly5759]

I'm dealing with a 77 Cherokee, 360 w/HEI, Holley 4bbl carb. It runs pretty good, occasional smoke on start up. In the warmer weather, it pings under moderate load-- say 35-40 mph with the A/C on going up a small incline.

The distributor is a no name HEI that was on the jeep when I got it. No EGR on the Edelbrock manifold. It also runs warmer than I think it should, ~220 on a mild spring day w/ no a/c on, ~230 with A/C on.



I have the initial timing at 10*, and using a dial back timing light, I get the following results:
Results @ 600 rpm = 10-12* degrees of advance with vacuum advance disconnected. (same with connected)
@1500 rpm = 28 -30* centrifugal advance only
@1800 rpm = 48-50 with vacuum advance and centrifugal combined.


How does the timing look? Do you think I am dealing with a timing or fuel issue? (Carb is clean, I've tried larger jets, plugs are showing white insulators as if they are lean/too hot.)

[FSJunkie]

I suspect it's too much.

10* initial timing at idle, no vac. advance.

The mechanical advance should start around 900 RPM and gradually build up to a maximum total timing (initial + mechanical) of about 35* at 4000 RPM.

The vacuum advance should add about 15* on top of everything I previously said, with the advance starting around 5" Hg and fully in around 15" Hg.

So at 2000 RPM you should see (initial + mechanical + vacuum) of about 40*.

[iapexl8r]

you say total timing.. is 1800 rpm's where the timing stops advancing? meaning if you increased rpm to 2500 the timing would not advance past 30 deg?
I have always (with vac adv disconnected)advanced the throttle until the timing stops advancing and noted rpm and total timing. 1800 seems a little low for total advance, but if it did stop advancing there that would give you 18 deg of mechanical advance. the rpm at which the full mechanical advance comes in can be adjusted by changing the flyweight springs(heavier springs more rpm) the the amount of mechanical advance can be adjusted by changing the bushing on the mechanical stop (fatter bushing less mechanical advance) there are also adjustable vac advance canisters that allow for some fine tuning.