frustration is definitley setting in...mild 351C rebuild...performer intake, 1406 carb, blaster coil, MSD wires, etc. am using an Accel 34202V distributor (dual point with vacuum advance) converted to Pertronix (timing chain at 0)...have tried everything humanly possible to get the timing right but no luck...distributor came with very light springs and 24 degrees total...got pinging...changed to 20 degrees total...got pinging....changed springs, many combinations using an MSD advance curve kit...heavier springs help but she runs "fat" (good term for sluggish)...with light springs she goes great and I can get by with a soft touch but soon as I get her into the throttle....pinging...no matter what fuel I use or advance curve I try I just can't seem to get rid of the pinging...also can't seem to get my intial timing above about 8 degrees advanced (no matter what curve I use) and if I get rid of most of the pinging with the heavier springs I can't seem to get my vacuum advance set up to work right (basically it is disabled right now)...I have read many posts as well as books/web stuff on advance curves...Ford rebuild book says to hook up vacuum advance to manifold vacuum rather than venturi ported...tried this but didn't really run great...don't know the mods to make this work...any and all help greatly appreciated....

Are you sure the timing marks on the balancer are correct?

What do the spark plugs look like?

Pertronix doesn't eliminate advance, Sam, you are thinking of dwell.

plugs look good....played with the advance curve and have it running pretty good now...the timing marks on my balancer are a bit off (TDC is actually about 4 degrees after TDC) and I have taken this into account...my question now is how is it that the stock Ford distributor was set at 10 degrees (20 crank) and factory timing (initial) set to 6 degrees....my math says this would give a total of 26 degrees (assuming the vacuum advance was locked out). According to everything I have read, I should be able to lock out my vacuum advance and set my intial as high as 16-18 degrees....not possible on my 351C...most I can advance it is about 8-9 degrees intial...comments (or am I completely out to lunch on this one???)

thanks

Place a glass of water on the air filter cover and when the water ripples are gone she perfect!

thanks for the tip...I will try it this weekend and let you know....CCW...so I will retard it till it bucks and then advance slightly...any suggestion on how much vacuum advance I should put into my timing? I have about 7 degrees crank due to vacuum right now...is that too high or too low...I am not greedy but I want snappy acceleration and decent fuel economy....

thanks again...

I think I have my problem solved...have 20 total in the distributor...initial set to about 8 and my vacuum is putting in about 9...I calculate this to total about 37 degrees...i have a relatively fast curve which maybe is why I can't lock out my vacuum and set my initial any higher...seems to be running fine now...idle is fine...appears to be no pinging upon hard acceleration...hope this makes sense and thanks for all the help (everyone)

Sure I'll jump in.

Vac. advance is in addition to mechanical advance.

They are two seperate mechanisms, one being affected by a ported vacuum signal and the other affected by rpm. Neither advance system can retard the spark (other than removing advance that they added), they only add varying amounts of advance. Since they work independantly of each other, the vacumm advance has to add to the total.

SteveW

thinking again about vacuum advance...I don't think that vacuum advance can in fact ADD to total timing...it can bring in advance under certain engine conditions but because of the mechanical stops in the distributor, it could never add more than what is there...I think it definitely changes the advance curve but doesn't affect total...

Under light load (high vacuum) the fuel charge density is very low, and extra timing can help the burn. Vacuum advance was developed to give the engine extra timing under these conditions.

Problem is... if the vacuum advance isn't adjusted correctly, it might not go away quickly enough, and the engine will see too much total timing.

As for the 351C, I'd try jetting up that Edelbrock carb a tad or swapping metering rods. Edelbrock tuning kits are available for these engines. Some Edelbrock carbs come calibrated a bit lean... especially the ones that are sold with electric chokes.

Good Luck!

thinking again about vacuum advance...I don't think that vacuum advance can in fact ADD to total timing...it can bring in advance under certain engine conditions but because of the mechanical stops in the distributor, it could never add more than what is there...

Craigber,

There are two different "mechanical stops". The mechanical advance moves the cam on the distributor shaft, and the vacuum advance moves the point mounting plate in relation to the cam. They are really seperate advance mechanisms and they are not limited by a common stop. Get an old distributor and check it out, I'm still with Alex on this one. Anyone else?

It's not a matter of voting, that's a fact.

In the interest of clearing this up, why would you connect vac. adv. to manifold vacuum? I don't understand that, because your max vac. signal would be at idle, and your maximum vacuum advance would be in at idle and lower as the throttle opens.

I always thought vacuum advance is connected to ported vacuum (a vacuum port on the carburetor above the throttle plate). Ported vacuum works opposite of manifold vacuum. ie. no vac at idle and max vacuum at w.o.t.

Am I confused about this? Shouldn't vac advance be connected to ported vacuum?

When you set timing, you disconnect the vacuum advance and set the initial timing. The advance curve is dialed in through weights and springs and checked at 3000 or so to verify that the 'total timing' occurs by the rpm you dialed it in for.

Then you hook the vacuum back up. The vacuum is a load sensing device, advancing the timing at high vacuum conditions, decelleration, going down hill, etc. It advances the timing beyound what the weights would for a certain rpm if it is needed.

So the statement that total timing doesn't include the vacuum advance is correct.

SteveW, the vacuum advance connect to ported vacuum, the retard, if equiped, to direct vacuum.

We just run mechanical too Steve. If it was a strip only car I wouldn't even run the mechanical advance, I'd leave it at 38 degrees and retard the spark for starting with with the ignition box.

This was a good excercise. An educational discussion, with some good input by our newer members and old alike.