Dual diaphram retard question
 

428 scj, 4sp, 391. Hi, looking for advise on the vacuum retard port on my distributor. I now have it hooked up directly to manifold vacuum and the outer advance port is supplied by ported carburetor vacuum off the holley 735cfm. The vacuum tree that was originally in the water neck is long gone and I'm useing the hole for my mechanical water temp sensor. I set the initial timing at 12* and when the manifold vacuum is hooked up to the retard port the timing drops to about 8* It idles nicely and runs strong no ping on hard acceleration and no deiseling when I shut off motor. I hooked it up like that thinking it would prevent backfires when decelerating and when I chop the throttle between shifts, It's probally all wrong and could run even better than it does. Any advise would be appreciated.

Loose the retard vacuum side. Set the base timeing without the vacuum hooked up on the advance side. Then check for total advance with it STILL disconnected. When your done, hook up the advance side again.

Vacuum advance is not present under full throttle (or deep throttle) conditions. It is for "crusing" down the highway when the engine can use a rather LARGE amount of additional advance for fuel economy reasons more than anything else.

Ernie

Thanks, I took your advise and just re-timed everything and here's what it looks like now---10* initial and about 25* from around 2500rpm and up whitch seems not to be enough? with the advance hooked up to ported carb vacuum the initial doesn't change but the total timeing goes up to about 36* does that sound right I test drove it and it still runs good I guess I need to find a drag strip somewhere.

36 total sounds good. Not surprising that you get some vacuum action sitting in the garage reving it up, the engine is not under "load", hence vacuum is present.

10 base plus 15 mechanical advance =25, which does sound a little on the low side, but maybe not! Figure 25 advance will ONLY happen under WOT (wide open throttle) and load (pulling the car). Anything less will result in more advance.

I personally DON'T like only mechanical advance. This is typically used for race type motors and the total advance SHOULD be carefully calculated (which it SELDOM is)!

Ernie

Car manufacturers did a lot of boneheaded things to their engines starting halfheartedly in the '68 model year, and wholeheartedly in the '71 model year to meet emissions requirements. In doing so, they took perfectly good 400 HP engines, and turned them into barely running 150 HP engines, and gashogs at that.

If you're one of the embarrassed former owners of a '70's factory stock musclecar, you vividly remember the emissions parts box, and the little, or not so little exercise you went through once a year to get your car emissions inspected.

The original distributor, carburetor, air cleaner, vacuum lines, and hot air hoses were reinstalled for your emissions test, then returned to the parts box until next year. Sometimes these emissions engines would barely run at all, and in some cases had to be towed to the test station. Worst, were the guys that had to store, and reinstall the entire original engine for emissions testing, then reinstall the "Good" engine to drive another year.

The Ford vacuum retard distributor was one of those items that spent most of its adult life in the emissions test parts box, and was installed in the engine for the day the emissions test was performed.

You see where I'm going with this, right? This was the time when women were burning their bras, and men were burning their Rochester Quadrajet carburetors.

To make a long story short, take your distributor into a shop that knows how to rebuild, and recurve them. Easier said than done as distributor recurving shops have gone the way of blacksmith shops with the advent of the iron horse, and computer controlled ignitions and EFI. (Thank our higher power for folks like Holley, and Demon who still know how to make carburetors.)

I think MSD now makes a Pro-Billet distributor for FE motors due to their popularity in Cobra reproductions.

So if the budget can afford it, replace OEM distributor with MSD or other quality aftermarket, and put your OEM Ford into the emissions parts box if you need this for your Cobra, or your local automotive museum.