Setting vacuum advance

[RustyRatRod]

I'm currently going thru this exact subject on my Mopar's. I started with the 74 440ci Ramcharger as it's only getting 6.6mpg, next I'll work on the Duster 360.





I also started a thread on RamchargerCentral to document my steps and before/after mileage for tuning the timing/vacuum advance
Vacuum Advance Timing for Maximum Efficiency

Same exact methods in the Mopar Performance engine books for fifty years. All anyone has to do is READ.

Thanks for posting, btw. Maybe in video format, it might reach more people. Especially since the MP books are getting impossible to find.

 

[halifaxhops]

I will chime in now.

 

[RustyRatRod]

I will chime in now.
View attachment 1715769424 View attachment 1715769425

I think the posts have remained pretty relevant.

 

[Demonx2]

No where did I see where you have told us what vacuum your engine will produce at idle and at cruz'n speed. You can adjust the vacuum advance all you want and it will no do **** if you have no vacuum to operate it.
OP - How much vacuum does your engine have?
Sorry if I missed it

As I mentioned above, I have not measured the vacuum levels yet. It's on the to-do list. I DO know that when I hook up the vac advance as-is, I get readings in the upper 50's to beyond 60 deg when holding rpm and trans in neutral. I also know that driving with it hooked up yields some noticeable roughness that goes away with the vac disconnected. So I'll simply be limiting the max vac advance amount to about 16-20 and seeing how that does.

 

[Demonx2]

A little follow-up. I measured the vacuum and have about 5" at warm idle in 1st gear at about 950 rpm. That's with timing (all mechanical) at about 13 deg.
2000-2200 rpm going down the road in 3rd gear is about 12" vacuum. Don't recall the spark mech advance number. (Cam is 251/256 @ .050)
The carb has an unknown power valve (no markings!!) so I have no idea if it is open at idle or not. I do know the engine is still rich at idle so going to try a 3" power valve just to see if it improves the rich idle condition. That may not work for driveability but we'll see. It will be awhile before I get to work on the dist to limit the max vac advance.