I don't have the loadomatic specs at hand, but I don't think you want to use those specs anyway.  Limit your total distributor advance to 10 degrees (20 crankshaft degrees), all in by 3000 rpm.  Set the initial at 14 degrees to give a total crankshaft degrees of 34.  If it doesn't like this much initial, add a couple degrees to the total and adjust the initial to suit you.  This is without vacuum advance being used.

John

The chart shows absolute pressure on the left axis - 14.7 psi is atmospheric pressure at sea level - so anything less is actually what is normally called vacuum (here in the USA). We old Americans on the other hand, are used to dealing with inches of Mercury - which can relate to this chart if you can find a conversion factor.

On the technical side - I assume that this spark advance curve is programed into a little logic controller that reads the absolute manifold pressure of the engine, the current rpm - and looks up the required number on this chart (at something less than the speed of light).

I'll see if I can find a nice conversion factor somewhere or invent one as the case may be ........ 

FDS12127A

Dist RPM           Vac.    Dist. Deg.

300                   .15"     0-1/2 deg

400                   .28"     1/4 - 1 1/4 deg

800                   .96"      6 1/2 - 7 1/2

1200                  2.21"    11 1/2 - 12 3/4 deg

1600                  3.41"     14 1/2 - 15 1/2 deg

2000                  4.60 "    16-17 1/4 deg

FDS12127B

300                   .16"       0-1/2 Deg

400                   .29"       0-1 Deg

800                    .88"      5 1/2 - 6 1/2 deg

1200                  1.27"      8 1/2-9 1/2 Deg

1600                  1.73"      11-12 deg

2000                  2.19"       13-14 1/4 deg

The Ford 1956 292 is identical to the second set above.

Buy or borrow a "dial back to zero" timing light - a pretty handy gadget when working on this problem. When the engine is revved sufficently to stop the mechanical advance - dial back to the "0" mark to show total advance (vacuum disconnected). With a tach on there, you will also know when it reaches the full advance point. I think for a starting point - use 10° static on the crank and 13° in the distributor (26° when doubled at the crank). When this is set right it will dial back to zero at 36 total degrees. Change weight springs to get the full 36° at 2700 revs - then if it doesn't knock try 2500. If you have to go up to cure a knock, go to 2900 and so on.     

I would suggest trying using the second one down on the right side of the charts. Use the "silver stop bushing" for a 25° upper limit and (1) silver (light) spring and (1) blue (light) spring. Set the initial crank timing at 10°-11° (35°-36° total timing) and go from there. Hoosier suggested a bit more initial so you can easily adjust to that by moving the distributor clamp. This is for the mechanical so the vacuum pot would be disconnected and the carb or manifold source vacuum plugged while testng.

The first page of the instructions says the supplied vacuum pot will deliver up to 10° advance at 15 lbs of vacuum. This is a non-sensical value - I suspect it should have been inches of mercury. Its also not clear whether that is a crank degrees value or a distributor degrees value. The vacuum pot in my modified Ford distributor strokes about 5/16" at full vacuum - which translates to 15° at the point plate and 30° at the crank. I am hopeful that they are talking about distributor degrees in the write-up, as you may need a bit more to work with for cruising economy.

There remains a choice - to use live manifold vacuum on the pot - or the ported vacuum also available on most modern carbs. It will jack up the idle speed if you use the live port and you will have to accomodate it when tuning your idle setting. There are active proponents of both ports (one or the other) on this site. Often you will find one works better than the other just by trying out both tunings. My experience - ported vacuum will heat up the engine a bit more if it is allowed to just sit and soak. But it it less troublesome when sorting out the idle tuning.

Good luck - you will not usually get away wiith tuning the curve and not paying attention to the carb too.

If the mixture is poor - and the resulting flame front is poor - you've got to light it sooner. Usually - cranking in the advance, makes a system systematically leaner - up to the point where it becomes explosive and knocks. This would suggest the carb is slurping a bit of fuel in there and the engine has to have all this advance to accomodate it. Does this Demon have the four corner idle? I had one of the 625 Road Demons on a Cougar - seems like you have to put a 1/4 turn on each of the secondary idle mixture screws for starters (?) Make sure the choke fast idle is out of your way (warm engine) - then you want to be sure the primary throttle blades are positioned so you can see about .040 or less of the transfer slots when stopped against the idle screw (do what you have to do to maintain this screw positioning).

When the above is true - the engine should run at idle and the carb ought to "answer" the two primary idle mixture screws. If it won't run - needs throttle opening - open up the secondary throttle blades a hair (I can't remember how this worked on the Demon) but not the primary blades. You should be able to see the results of primary idle mixture screw adjustment on a vacuum gauge (tune each for highest vacuum) - if not - first try closing the two rear idle screws to less than 1/4 turn. If that doesn't work - usually it means the carb is leaking fuel into the intake from an uncontrolled source. Often that source is a power valve. I have also had a valve that was marked 6.5 (the inches of mercury where it opens) replaced it with another 6.5 and it still screwed up the idle until I replaced it with a 5.5 (?)   

An open center carb spacer can screw up the way the primary mixture screws behave as one will tend to "dominate" and govern the system by providing idle fuel to both sides of the manifold. I think street engines behave better with a divided spacer so the the "180°" manifolds do what they are supposed to do (and cut venturi pulses in half).     

I don't believe it is even close to normal to have an engine sitting there at idle with 20+ degrees of initial advance. To my thinking Mike's outfit is way rich and he is basically "leaning it out" with spark advance. With a fairly ordinary advance curve in there - operating the accelerator pump is dang near putting the fire out. Any time you can solve (or mask) an accelerator pump issue by adding advance - warning lights should come on.

Ford built about a zillion carbureted cars and trucks that had relatively small amounts of initial spark advance and lean idle settings. I won't say this arrangement was great for get-up and go - but it started OK, drove a lot of guys to work, wives to the grocery and went cruising on Saturday night. When I looked at the Demon web site for spec's on the Road Demons - it appears that the 525 and 625 models have the same throttle blades but differ only in the idle bleed, main jet and booster specifications. A 300 cubic inch engine at 500 rpm is only going to consume about 45 cfm at perfect efficiency (sucking every cubic inch of air it can). That's about 20-25 cfm at each venturi. Those Demon carbs were originally calibrated for modern v8 engines that ordinarily idle at higher rev's and have more cubic inches to feed. So the suction "signal" at the primary is going to be way different than the carb was wet tuned or calibrated at the factory. 

I have to get headers/exhaust back on this week and then I can atleast start it again and do some tuning.  - John

I think the "four corner idle" is wasted on a 180°, dual plane, cross "H" pattern intake manifold - so setting the secondary idle screws back a bit more than BG suggests is just par for the course. The four corner set-up seems to be most helpful with a single plane "X" type manifold - where you really are feeding four corners.

Two more things to try - drop the float levels a bit lower than the center of the sight glass - and put the "plain" or black spring back in the vacuum secondary pot. The lower float levels take away any tendency of fuel to "pull" out of the boosters at idle - you still aren't lean enough if you have to jack up the advance the way you do. You ought to be able to make this engine "knock" by over-advancing it.

The engine can't use all of the secondary air volume this carb can deliver - so the quick opening allowed by the light spring - is giving you a false feeling of acceleration. The "cut-in" rate of the secondary opening should be smoother than we often think.

Good Luck! 

        Steve's right on the money on the Demon, keep it. If you start comparing the pieces of each carb to the other, you'll throw that Holley away.  I run one on a 408" Windsor in my pro street Ranger. It's 3 tenths and a couple miles per hour quicker than a 780 Holley on the same vehicle. Once it's set it stays set. Love it.

                                                     Frank/Rebop