Want to add Vacuum advance!!!

[HALIFAXHOPS]

Manifold vacuum will be full advanced at idle just say 15inhg, as it revs it will drop to say 10inhg. Not a good idea it will work backwards. You can lock it out and make it full mechanical which is what i would do, you just have to find the springs and cam to do what the engine wants. First thing is to figure out what the engine wants for a curve IMO.

 

[Meep-Meep]

Anything below the throttle blade is full manifold vacuum. i.e. throttle shaft centerline more or less.

What you can do to determine the throttle position while cruising is to set up a protractor sort of gauge with a pointer lever that will move with the throttle arm but stay put after you go back to idle or a zip tie collar on the cable? The idea would be to gauge how much your throttle is open during normal light load cruise. Back that up with a vacuum gauge reading on the fly. Then look where the pointer stopped and note the angle of blade opening. The hole in the carb should be above the blade at idle and under the blade while cruising (the blade will expose the hole to manifold vacuum while cruising). For reference look at an oem carb or a Holley 750 (or similar) to see the location of the ported port. Once you determine the hole location mark it then take to a machine shop and have them drill and tap 10-32 with a spotface for a seal. Then get one of these 10-32 air fittings or a small hose barb. This assumes there is not enough wall in the carb body to put a 1/8" or 1/16" pipe fitting. I bet it's cheaper than EFI. Unless you want EFI then disregard this.
https://www.grainger.com/category/p...-fittings?attrs=Pipe+Size|10-32&filters=attrs

 

[1 MEAN66]

1mean66 I hope that tarantula looking vacuum fitting didn't sway you away from the intake as a source for vacuum advance. Those fittings come in many shapes. I attached a pic of the one on my 6 pack manifold. Most manifolds will have a 3/8 inch pipe thread port for vacuum to operate power brakes and other accessories.

View attachment 1045629

No Not at all. Have all kinds of them at home in the shop. Have spun wrenches since 68. I am just trying to figure out where to put it. If a take my time (usually don't) I can just cap anything that does not do what I think I want it to do. As stated else where if I got a sniper injection it solves everything except cost. Car is becoming a driver, and it is definitely not a show car. It goes to shows, but we invite all the little ones to climb in it and have fun, they love the "monkey bars". What I think I want is the vac. to start tipping in at about 2K. And I do realize that any time the throttle moves that advance "goes away". If I tap the manifold I will have it lower than that. Thought tapping carb. spacer would work , but may be to high in intake passage. But I'm thinking I will try it there first ( have an extra 1" spacer) cheap ( inexpensive part) to screw up. I actually but a vacuum port in my valve cover. Sure now your thinking What is wrong with this _ucking idiot?
Had scavenge tubes on the headers on our little engine (525HP) Put TTI's ( 1 7/8's ) on this motor. Added a full vacuum pump system ( 4 vane, hoses, AN fittings welded to covers, separators, etc.)to act like the PCV system. All Moroso stuff. It worked so well it could suck oil out of the custom aluminum covers. So built baffles in them ( used Stainless wall switch plates w/o the switch holes - they fit perfect and the beveled edges let oil drip back in on valve area). Still the pump could really pull vacuum! I found out how much by putting that port in the l/side cover. Almost 30" of vacuum. So added a "bleed valve" more Moroso parts. Now I run at most RPM 9". So now Have negative internal pressure. Still have to drain the separator and breather once in a while (100 miles or so). But it worked. So ya see, I like to piddle, sometimes ( maybe most of the time) take the long way around, but it's part of the fun. I guess that's what I am trying to do here. Just look at all this typing. I should be doing sheet rock in the basement.

 

[1 MEAN66]

Completely agree. But the vac advance needs to be ported and the strong signal in proper position with the throttle blade at light load cruise.

Also agree.