Resetting/Tuning Mechanical and Vacuum timing advances

[SadbutTrue]

Hey, as you might or may not know, I recently semi-solved a bad ping with judicious use of rich jetting. I have an Edelbrock 600 that seemingly worked wonderfully for 2+ years, but I started developing a horrible ping a efw months ago. Long story short, I bought the carb calibration kit for this carb and had to go to the richest jetting the kit would allow to get rid of the ping. And it still pings a little when its hot outside, been driving for a while, and is pushed (either up a hill or through spirited driving...).

I think I might have just band-aided the problem, and I'm worried my gas mileage will plummet with these jet settings, so i think I need to at least look at timing.

How do I reset mechanical and vacuum advances? The ping only occurs at high cruise and near full throttle (though not at full throttle), so I think if its timing, it has to be advanced timing. Do I need to get an aftermarket vacuum advance to be able to mess with it?

Thanks

 

[slapper]

Hopefully not.
Inside the vacuum diaphram where the vacuum hose connects to the distributor, there may be a small allen screw. Turning this inward slows the rate and vacuum level of vacuum ignition retard, and turning it outward increases the rate.
As far as the mechanical goes, you can remove the distributor breaker plate and see if the small black cushions on the ends of the reluctor tangs are worn off, or fallen off(common).
Personally, I hate running pig rich, and perhaps a quick dyno tune with an air/fuel reading would help. Additionally, the distributor could be set up on a SUN machine to taylor the rate of mechanical advance.
I usually will set the reluctor to the widest setting(14 or 16 most of the times), and then I know I'll get 28 or 32 degrees of mechanical advance. Then I can play with the vacuum on the car to fine tune.
I had a distributor one time that saw about 41 degrees of mechanical, so I just put a quick tack on the inside of the reluctor tangs, and then using a dremel, ground it every so slightly to get the correct mechanical advance.
Kinda hokey I know, put it's still working today.
(sorry so long winded)
Later.

 

[ForceFed70]

Why not test to see if it's the timing that's actually at fault?

Simply retard the initial timing, which will also retard your total timing. If that stops the pinging, then start messing with your mechanical and vacum advance. If it doesn't help, then start looking elsewhere.

 

[SadbutTrue]

also, a guy i was talking to today implied that I would only have a vacuum advance, not a mechanical... is that true? I was always under the impression I had both.

What do the relucter tangs look like, I'll take a look at those this weekend.

 

[crushnut]

also, a guy i was talking to today implied that I would only have a vacuum advance, not a mechanical... is that true? I was always under the impression I had both.

What do the relucter tangs look like, I'll take a look at those this weekend.

Like these:

 

[Ozsum2]

Instaed of jacking with the timing, why not just pull off the vac line and plug it. Go run the car and see if it stops. That will tell you the story.

 

[crushnut]

Instaed of jacking with the timing, why not just pull off the vac line and plug it. Go run the car and see if it stops. That will tell you the story.

So simple, yet so effective

 

[SadbutTrue]

well i was going to try that, but right now we have the carb set to run real rich just because I was tired of the pinging and it was easier (we rejetted the thinga nd all). So I don't know if I'd hear a difference even if it was there.

 

[Ozsum2]

I disconnected my advance while waiting for the new dist. to come in. I opted for a new one, rather than rebuild the springs under the points plate.

 

[SadbutTrue]

aight i'll mess with it this weekend, prolly time it first, see if i can see where the timing is at, and if its too advanced then de-richen the carb some, get a new vac advance and check out that mechanical advance for problems.

 

[Max Power]

If you had no problems for two years and then you started to get pinging, I am wondering if you have a vacuum leak somewhere that caused the leanness and you are masking it through jetting.

When something changes like that, I always look for the cause of the change rather than change something that you know couldn't have changed, like jets.