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Old 04-25-2011, 06:31 PM
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Vacuum adjustment help needed

I have a 428 with tripower that I have been trying to fine tune. I have a initial timing of 30 degrees. With vacuum plugged it run, pulls through all gears great. But tends to run hot of course with out vacuum hooked up. It has a total advance ( tested without springs on at ideal) of around 62. I bought a crane cam adjustable vacuum with a adjustable canister and a timing limiter plate. I can't find the right adjustment combo to smooth out the car when it cruising( jerks ). I went from one end of the timing limiter plate to the other end all the while adjusting the canister in and out as well. It seems as I added limit to the timing plate it backfired alot, but ran a little smoother cruising. It runs the opposite the other way, doesn't seem to backfire as much on deacceration with the plate not so restricting but tend to jerk when cruising. Do I have to just keep tinkering till I find it? Am I missing something here? I have a MSD ignition with ingnitor magnetic pickup. Thanks for any enlightenment. Be back in a couple hours.

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Old 04-25-2011, 09:05 PM
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Describe the distributor, stock pontiac 428 type with ignitor retro fit? ignitor or ignitor 2. What cam as in duration, what car, rear gear, auto or stick, if auto what is the advertised stall on the converter

Try the base setting on the vacuum can at 7 turns out CCW from all the way in CW then go from there, CW decreases the amount of engine vac needed to start adding advance effectively giving more advance over the range of engine vac. CCW effectively decreases the amount but it depends on what your engine vacuum is capable of,,,what are the vacuum levels at idle and at part throttle cruise?

The limiter plate goes in to limit the total travel of the vacuum can rod thus effecting less advance, something is not right it is not doing its job.

The surging is most likely due to over advance and/or lean AF mixture

Why so much advance? 30 is not bad total at idle but 60 total may be over doing it.

Shoot for 16 base + 18 mechanical + 15 vacuum advance on manifold vacuum that may be a better place to start.

I find it is much easier to pull the dist and install the parts on the bench, you can actually measure the rod travel when putting the limiter plate in and also work the vacuum advance can with a vacuum pump and make sure its all free moving etc.
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Old 04-26-2011, 11:49 AM
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64 Gto, stock distributor with ignitor 1, msd ignition, 4 speed muncie, 3.2 rear, 20/20 cam. Runs great at 30 and I took springs off to find total advance around 62. Stock advance wts. Runs great without vac. hooked up. just can't find right dial up. I sorry CW? CCW? Try and to dial down intial advance and it starts to spudder at 20. Not good to set at 30 hook up vacuum and then dial turn down advance? thanks
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Old 04-26-2011, 04:16 PM
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You must do this first:

Check for top dead center and make sure your damper timing marks line up with the pointer tab. What this is for is to assure you are actually at 20 degrees initial timing when you use your light, your damper or timing marks could be out to lunch as in wrong.

I don't have the link and the site is down search 'crankshaft coalition determining TDC'

The engine should idle fine as low as 10 degrees BTDC, I suspect your reading is wrong somehow or there is something else causing it to stumble ie carbs, plugs, wires, fuel issue etc. Start by verifiing the timing marks.

Are u using a dial back timing light? if not make a timing tape.

For the mech advance curve,,,Put one heavy and one medium spring in it to start with, you should not run without springs. Start from the beginning.

CW CCW is the direction you turn the allen head screw in the vacuum advance can. Start by turning it CW all the way in till it bottoms out, don't over tighten, then back it out CCW (counter clock wise) 7 turns, this is just a place to start you may need to adjust later but 7 turns it will get you close.
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Old 04-26-2011, 09:06 PM
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vacuum adjustment

I did check and make sure I was TDC on plug one by pulling plug and rolling it over till it blew my finger off hole. I have a O, 5 degree mark on my Harmonic Balencer and I marked a 30 degree one as suggested by a couple engine building authors. I do use a dial back and have caught myself with it dialed to 30 or I bumped it reads differently but when I put it on 0 it always tunes in best at 30 line or right around there.CW CCW clockwise,counterclockwise oh I get it!!!!! I couldn't figure out what those stood for. Should I start the plate first at the most advance, with the 7 turns? or should I start that plate in the middle as well? I been through the whole spectrum with both but am will to try again if the right combo somewhere in there. the springs I had a blue and silver and am going to try a blue and yellow which allow it to advance at lower rpm, maybe that will help as well? thanks for advise
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Old 04-26-2011, 11:15 PM
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Quote:
Originally Posted by vbreithaupt
I did check and make sure I was TDC on plug one by pulling plug and rolling it over till it blew my finger off hole. I have a O, 5 degree mark on my Harmonic Balencer and I marked a 30 degree one as suggested by a couple engine building authors. I do use a dial back and have caught myself with it dialed to 30 or I bumped it reads differently but when I put it on 0 it always tunes in best at 30 line or right around there.CW CCW clockwise,counterclockwise oh I get it!!!!! I couldn't figure out what those stood for. Should I start the plate first at the most advance, with the 7 turns? or should I start that plate in the middle as well? I been through the whole spectrum with both but am will to try again if the right combo somewhere in there. the springs I had a blue and silver and am going to try a blue and yellow which allow it to advance at lower rpm, maybe that will help as well? thanks for advise
TDC is found with a piston stop not your finger.
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Old 04-27-2011, 08:55 AM
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Does it mount on cylinder 1 hole? How does it work? Does it show travel of the piston, I assume.
The the shortest reading is TDC? Thanks
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Old 04-27-2011, 06:10 PM
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30* initial and 64 Total. You are doing something wrong. 64 BTDC would be detonating like mad. I think you need to look at everything one more time
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Old 04-27-2011, 08:13 PM
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vacuum and timing issues

could it be my harmonic balancer was not put on right? Maybe its reading 30 but really its 0 or 5? I mean it runs good with the vac. plugged, idles nice, starts nice, lays rubber nice. Just not as smooth in cruise mode with the vac attached.
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