[DeTomaso] Cam change and Vacuum Advance distributor

[JDeRyke at aol.com]

In a message dated 2/27/09 6:35:52 AM, tborcich at msn.com writes:

> I was curious, once you change the cam to higher performance specs as 
> follows, should anything be done to the (stock) distributor advance since vacuum 
> will change?
> 
Ford's stock dual points distributor was a complicated push-pull system of 
vacuum and pressure. It'll work OK with a street cam if you fiddle with it. 
Points-dwell should first be set to 32-35 degrees combined, with each set of 
points set to 26 degrees. I daresay you won't find a tune-up shop today that even 
knows what 'dwell' is.... Vacuum advance is a supplement to initial plus 
centrifugal advances, intended for light load street cruising. Be sure you have the 
advance line hooked to PORTED vacuum- that is, hooked to a spigot on the carb 
body, not the throttle plate, where there's no advance with throttle closed 
and max advance with WOT. This is NOT manifold vacuum. Inside the distributor, 
there's a pin protruding thru the moveable advance plates. Stock, there was a 
rubber bushing on the pin to limit vacuum advance to 'some amount'. Various 
sizes of bushings were once available from Ford. The bushings are always gone or 
badly rotted, so some add a tiny bushing made of copper tubing, and hand-file 
it to 'adjust' max vacuum advance. 
On some vaccum advance cannisters, there's a needle valve inside the 
cannister that adjusts vacuum with a small allen wrench thru the hose spigot. They are 
never externally marked so the only way to find these is to stick a wrench 
inside and see if you can find any adjustment. After setting the initial plus 
centrifugal advance to no more than 36 degrees total with vacuum hose plugged, 
vacuum adjustment is done so that when cruising at light load with 'some' 
vacuum present, no pinging results. This may increase fuel mileage a bit- or not. 
You'll soon find out. My Ford electronic distributor has vacuum advance but I 
capped it since I found it made no difference in running or economy. Good luck- 
J Deryke


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