I am doing the road tuning on a 289 I rebuilt and determined that the vacuum advance curve on my stock Ford distributor is making my engine ping on the highway at partial throttle.
When the vaccum drops below 10 inches the thing starts pinging. Once you punch the throttle and drop the vaccum below 5 inches it stops pinging. After I disconnected the vaccum advance on the distributor and recreated the situation on a highway it went away.
I know I need to play with the advance curve. The distributor is stock points with pertronix.
What I wanted to ask was if anybody has experience with this Crane part and can tell me what would be a good rpm to set up the advance curve to reach its full advance at 3800 3500 or 3100? What's stock Ford?
Should I just leave the stock springs and then install the new vaccum advance unit supplied with the kit and use the allen wrench to eliminate the ping?
The engine is a 289 with 70 351W heads, a Comp Cams .480 .480 retrofit roller cam, with 9.6:1 compression, edelbrock performer dual plane, Holley 1850C (non adjustable secondaries) vaccum secondary, manual chock carb. It's in a 67 Bronco on 35s and cruised at 2000-2500 rpms on the highway.

 

What do the plugs look like, not running too lean is it?
The adjustable advance will make tuning easier.
I would try setting the total advance to 34* @ 3500rpm and see how that does for a starting point. It should be close.

 

I disconnected the vaccum advance, which made the ping do away.
I pulled the plugs with the 64 jets that the carb came with and they porcelain near the electrode was a deep orangish-brown-clay color. It always seemed to be running rich by the smell of the tail pipes coming in since the back window of the soft top is off.
I put in 62 jets, which got the odor to disapear, and then after about two days of driving, over ten miles, I checked the plugs again. They were a little lighter and had a little brown to the burn on the finger where the spark jumps from the electrode, whereas before that was totally black.
It stumbled a little off idle, which makes me think it might be slightly too lean.
However with the 64 jets the vaccum on the guage was 16 inches at idle, now it pulls 18 inches at idle.

What do you think on the plugs?

If I am reading you right I should set total advance for 3500 and then tune the vaccum advance to max out at 34*

 

The allen screw will only adjust how much vacuum it will take to move the plate not how much it moves, although it will limit the movement. All it does is change the spring pressure.

Here is what I do.

Put a vacuum gauge on the ported vacuum port on the cab, (no vacuum at idle) and get the gauge where you can see it while you are driving. Take it out on the free way and let it pull in 2nd until it is at max rpm, and keep an eye on the vacuum gauge. Note the reading.......also note the reading at cruise speed and just off idle.

Put timing light on it and a vacuum pump with a gauge hooked to the vacuum canister and start pumping, keeping an eye on the timing marks. When the marks start to move look at the gauge and note the readings. Now adjust the screw so it takes move vacuum to move the timing than it has at wot.

Also find out how much mechanical advance the distr. has this will help you with off idle stumbles........

I take the vacuum off and set the timing to 0 and then rev it to 4000 and see how much it moves.

I would start at 38 degrees total...so if you have 28* mechanical set the initial to 10*..... But if the vacuum advance is working at wot it will pull the timing to the moon. That's why you need to find out how much vacuum it has at wot and adjust the canister appropriately

I run my 302 at 38 total 20 mechanical and 18 initial, although I pulled it back a tad on the dyno to 36 total….

Love those Duraspark distributors… easy to set up and adjust.

Hope this helps………….

 

forgot I like mine in by 2500......

 

The plugs sound about right now. You probably need to step up to a 28 squirter if you have a 25 now to eliminate the slight hesitation once the timing issue is corrected and itis still there.

 

Thanks for the help. I am working through this stuff and I will let you know how it works out.