Ok, I have been doing some thinking and research on this spark advance problem with dual carbs. I have never really taken the time to figure out how everything works but I am learning. I understand that the original 49-53 distributor works on vacuum advance only (no mechanical advance) works good with a single carb but there are low vacuum problems with a dual carb setup. I believe some testing is neccessary here. I am going to fire my flathead for the first time with the original distributor and a single Holley carb, get it running and make sure all is good. I plan on building an electronic ignition distributor out of a Chrysler 318 model, now this distributor has both a mechanical and a vacuum advance (but I believe the vacuum advance works backwards than a original unit). Now by playing with the mechanical advance hopefuly will be able to follow the engine RPM and possibly for load compensation if I hook the vacuum advance to the intake port (where the wipers get there vacuum) it should see engine vacuum and decrease with load, stock distributor vacuum increases with throttle, more playing around.

Has anyone tried using both the mechanical advance and the vacuum from the intake to follow the load and RPM.

Thanks for your comments

 

you should never hook up your vacuum advance to manifold vacuum. Manifold vacuum decreases during acceleration and ported vacuum increases. I have not read the article that you posted, it was very intresting. I got my info from the ford manual and ac ouple of articles I have read. I have never run a multiple carb set up before so I never really woried that much about it. I am planning on running a blower on my engine and was told by joe abbin at roadrunner engineering that my stock distributer would not work with even a single carb and a blower because of the change in vacuum signal he didn't recomend a single 94 for my aplication even though I am keeping my rpms below 3500, so I may be looking into running dual carbs in the future and will be doing my research now as well.

 

I better back up a little, what I am going to do is get the engine running as stock then change to the Chysler electronic version that has both the mechanical and vacuum advance, I quess what I am hoping is that I can adjust the mechanical curve to run OK and maybe even use the addition vacuum advance to make it run better. I sure all this has been done before and as there is lots of info on the net, there is probably too much. I am going to go ahead and build my Chysler electronic as that is the parts I have and try it. If anyone knows of any other good articles I am willing to learn.

Thanks

 

F6Guy is correct, manifold vac is no good for vac advance although there are several guys on the web who claim it is the correct way to do it (and they are almost all drag racers running very high compression and fat jets, not sure why they even run vac advance). The MoPar vac advance works exactly the same as the stock Ford : More vacuum = more advance.