Cali,68,L-79

I installed the new vacuum advance and removed the old one, not at all old maybe 6 months old


In my haste I removed the Pertronix - 2 ignition which was not required and when I couldn't get the magnetic ring around the ignitor I stupidy cranked it over and bent thehell out of the ring and bent over the ignitior and it's base Spent the next 2 hours rebending the units and reinstalled, keep in mind it never had to come off and used my vacuum pump to verify full operation of the vac canister. Well put it together and retimed the car for 36 degrees by 2600RPM.

and then with the cannister adjusted for minumum advance I timed it and got


61 degrees!! Reread thedirections and even tried clockwise max and got 61 degrees I thought WTF??!!!! Now there is the cam devisce but it has only 6 indents and that's 12 degrees. I'm damn near 20 degrees too much advance.
It fits here.



Anyway I can't figure this out. Wasted $30 for the kit, almost destroyed my ignition and 3 hours and am back to the same friggin point I was last week. NO VACUUM ADVANCE!!

:banghead: :banghead:


[Modified by Cali,68,L-79, 11:19 PM 4/5/2004]


[Modified by Cali,68,L-79, 11:24 PM 4/5/2004]

Cali,68,L-79

delete edit


[Modified by Cali,68,L-79, 11:20 PM 4/5/2004]

71coupe

Don't be so quick to trust the timing mark on the ballancer. I put a new one on my motor 2 years ago and it's already slipped. The only way you can be sure it's accurate is to replace it, or check it with #1 cyl at TDC. Another thing to consider is that chevy had several timing tabs (hopefully the correct one is on your motor).

:cheers:

SLine78

I was recently down this road. Purchased the Crane Adjustable Vacuum Advance Kit in anticipation of using it when I overhauled my distributur recently. You need to use the included Vacuum Timing Limiter because the adjustment with the hex wrench only adjusts the rate of change but not the total amount of advance. You want to be at 52 total and your at 61 so that would be about 4 notches on the Timing Limiter.

I noticed that your original vacuum advance unit was a B-19 which according to Lar's Vacuum Advance Timing Paper, provides a maximum advance of 12 dsitributor degrees. With this advance unit you had about 60 degrees total advance. You want something that only produces a maximum advance of 8 distributor degrees.

After reading Lar's paper I decided it was easier to stop by NAPA and pick-up a B-22 advance unit and install it instead of messing around with the Crane unit. The Crane unit may get installed someday as a final tuning aid, but for now it is just sittlng in the box.

Mike

Fevre

Did you re-set your base timing after installing and adj the limiter? It advances the base timing by 2* for each notch you use so if you used 1 notch your base timing would be adv by 2* unless you re-set it.





[Modified by Fevre, 9:06 AM 4/6/2004]

Jughead

What's that atop the carb? Looks like an air cleaner spacer?

Fevre

Just noticed you did not use the limiter, the vac adv adjustment only controls the rate of the vac adv not the total vac adv. You need to install the limiter plate and follow the directions. That plate does not fit in my MSD dist so I made my own limiting plate with sheet metal. I had to do some trail and error to get it where I needed but it works none the less.

Before you write it off try installing the limiting plate and see what happens.

Again make sure you re-time it after installing the limiter and setting it, time it just like you would normally starting with the vac adv unhooked and proceed from there.

vettfixr

:iagree: I had the exact experience with the Crane unit. It's somewhat misleading of them to say their advance unit is adjustable for the amount of timing it will give when it really isn't. The limiter device is what limits the amount and you could probably use just the limiter or jury rig a limiter to do the same thing with a conventional vacuum can. I used what Lars recommended and never looked back. It works fine.

Cali,68,L-79

Fevre thanks. Re-read the instructions over a cup of coffee. Still confused as to how many notches I must go. I've got max 40 degrees@4000RPM with the weights. If the cam adjusts by 2 degrees then I need to back it down 2 degreess. i.e. I'll have 38 degrees at 2500RPM instead of 36 degrees at 2500 RPM right? See I never use idle timing but it is 19 degrees at 900RPM, all I use is 36 degrees @2500 RPM when I time the car.

Second note when the cam is in and I get 52 degrees total then how do I adjust the rate? i.e. do I turn counter clockwise to loosen the tension on the diaphram thus increasign the rate at which it approaches max timing or what? Will adjusting the rate affect total timing or just the rate at which it gets total timing, i.e. all the way clockwise it goes from 40 (weights max) and reaches redline before it sees 52 or if it was turned all the way clockwise it would go from 40 to 52 degrees almost immediately? Is that about right???

vettfixr

Cali
If I recall correctly the limiter doesn't fit in our distributors like it does in the non-tach drive. I believe you have to do a little filing and I think I remember having to put it in upside down. The instructions mention something about this.

lars

I've never had much luck with, or need for, the adjustable units. You're much better off determining what your needs are (length of desired vacuum curve and pull-in points) and buying a fixed unit that meets those needs. Being the opinionated old guy I am, here's what I would do:

Put that Crane adjustable unit back in its box and put the box up on a shelf someplace. Give it away to the fist guy who asks what it is - tell him it's a speed part that will make his car go faster and get rid of it.

Then, hike on down to NAPA and buy part number VC1810. This is a fixed vacuum advance unit that will give you 16 degrees of maximum advance. It starts pulling the curve in at 3 to 5 inches of vacuum, and has the full 16 degrees pulled in at 6 to 8 inches. By setting up your total mechanical advance to 36, this unit will give you a combined maximum total of 52-54 degrees - exactly where you want it. It will also pull in its full advance at idle vacuum, giving you stable reliable timing if you choose to run it off of manifold vacuum (as opposed to ported vacuum, which you can also use depending on your tuning needs). No adjustments required, and you get exactly what you need right out of the box for about $12.

SpyderD

It's a trial and error process, at least it was for me. As everyone said if you adjust the cam/limiter plate it will effect your intitial and total timming so if you move the limiter 2 notches and that decreases your total vacuum advance 4 degrees it will also increase your initial and total timing (with or without the vacuum can hooked up) 4 degrees. Don't sweat it to much - move the cam a few notches, reset your initial and total with the vacuum can disconnected to what your engine likes best (i.e. -what it was before you moved the cam a notch), reconnect the vacuum advance, go for a drive. If you get a ping at load or going up a hill repeat the process.

In my experience don't even worry about that hex screw that loosens or increases the tension. It only effects the vacuum point at which the vacuum advance kicks in and, in my experience at least by playing with a vacuum gauge, it does not impact too much at all. You screw it in and out about 40 turns and it will slightly change the rate of vacuum kick in from 12 psi to 15 psi - not much impact and used for fine tuning only. It does nothing to effect the amount of timing the vacuum can gives. Use the limiter/cam plate for that.

Cali,68,L-79

Thanks LARS I'll search for it after work. Probably return the Crane unit.