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  #106 (permalink)  
Old 05-24-2019, 12:30 PM
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Re installed OEM weights using one heavy and one med spring. Had a bad intermittent miss at all speeds. swapped out cap and coil from another OEM unit and that fixed it. 19* @1050 23*@1300 30*@1700
with both heavy springs 19*@1050 21*@1400 33*@2800 Added ported vacuum 42*@3000 using limiter at about middle of cam. It idle's in gear at 750 rpm. even drove it around the block. It's a little hard starting at 19* and wants to run on when Its shut down @ 1050rpm.

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  #107 (permalink)  
Old 05-24-2019, 06:26 PM
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Looks like you made some decent headway

You'll want to rev it past 2800 rpm while doing your timing curve check, up to near 4000 rpm to find out if the centrifugal advance is truly fully advanced, as I don't believe it is at 2800 with that spring set on it.

Hopefully, it is advancing some more past 2800 rpm, as that will give you the needed room in the timing curve to allow you to back the initial down to 16-17 to make starting easier.

Then we can get into fine tuning the carb and see if that run on after shut down can be taken care of
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  #108 (permalink)  
Old 05-25-2019, 08:09 AM
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Ok so mechanical advance does go up to 37*@ around 3500rpm. So lighter springs and back off the timing a little, Right? I want around 34* before 3000rpm
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Old 05-25-2019, 10:07 AM
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Quote:
Originally Posted by Goneagain View Post
Ok so mechanical advance does go up to 37*@ around 3500rpm. So lighter springs and back off the timing a little, Right? I want around 34* before 3000rpm
Ideally you want your MAXIMUM centrifugal timing to be around 34-36, and you want this point of maximum timing to occur at or before 3000 rpm. If your point of maximum centrifugal timing is at 4000, then that is the RPM where you set it.

First you need to map your timing by increasing RPMs until you get no more centrifugal advance. You will see the timing stop advancing as you rev the engine. This could be as high as even 4500 RPM or more, depending on your springs/weights, so don't stop the initial revving at 3000 or 3500 until you know where it stops advancing.

Then you would set timing to 34 at an RPM somewhere above that point of maximum centrifugal advance. If you change springs or weights or both, then you need to determine the RPM of max advance again for your new combination of springs/weights. Failure to get this right could result in detonation and subsequent engine damage. It's important to know your maximum timing under full power conditions. Since vacuum is essentially zero at full throttle, vacuum advance does not factor in and it ends up being all centrifugal advance.

You should be able to choose springs to go along with their weights from the Moroso instructions.

Last edited by 2001Blazer4x4; 05-25-2019 at 10:23 AM.
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  #110 (permalink)  
Old 05-25-2019, 10:48 AM
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Yeah the curve stops at 37*@3500 now. I ran it up over 4200with no change.
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Old 05-25-2019, 11:23 AM
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Quote:
Originally Posted by Goneagain View Post
Yeah the curve stops at 37*@3500 now. I ran it up over 4200with no change.
So you can back the timing up 3 degrees if you want it set to 34. This should lower your initial timing a few degrees and make it easier to start as well. you may very wll have the right combo of advance weights and springs, Max centrifugal at 3500 is not bad for a HEI. If you put lighter springs on it, you will almost certainly be back to the idle being already into the timing curve (and that is the entire thing we are trying to avoid). Run-on will not be affected by timing, since ignition is turned off at that point. Hopefully should be able to get engine running better and close the throttle more at idle - that is the cure for run on.

Now can you please slow engine down as much as possible, and map the timing from maybe 600rpm up to 1300 in 100 rpm increments by adjusting the idle screw and letting it stabilize at each RPM before taking a timing reading. This would be a double check of the lower timing curve before moving on to vacuum advance and finally carb adjustments.

Will we be working with the Crane Vac pot or the Echelin? Will make a difference on how we hook it up and adjust. We can go either way.

Last edited by 2001Blazer4x4; 05-25-2019 at 11:44 AM.
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  #112 (permalink)  
Old 05-25-2019, 05:04 PM
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OK so here is what I have now
16*@1050 and below
17*@1200
21*@1400
23*@1600
24*@2000
26*@2200
28*@2500
30*@2800
Should be maxed out about here.
32*@3200
34*@3500
I have the Echelin on it and get 40*@3000 and up with the limiter set about mid way on ported vacuum. correct me if I'm wrong but I should adj limiter to get max vacuum adyance.

Last edited by Goneagain; 05-25-2019 at 05:17 PM.
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  #113 (permalink)  
Old 05-25-2019, 05:24 PM
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I think your centrifugal curve is pretty much perfect! Good job!

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  #114 (permalink)  
Old 05-25-2019, 05:36 PM
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You may be able to run manifold vacuum with the Echelin vac advance I suggested. Doing this would give you additional timing at idle and this should allow you to maintain idle speed with the throttle blades closed a bit further (helps fight run-on). So plug the vac advance into manifold vacuum and adjust the idle speed to 1000 rpm in park. Starting with the mix screws turned out exactly the same, turn each in 1/8 turn until engine vacuum just begins to drop. Then back off to the last setting. Note vacuum reading in park and timing in park. Then drop into gear and note vacuum reading in drive and timing in drive. Report these back. Good luck. I think you're on the down slope now!

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  #115 (permalink)  
Old 05-25-2019, 05:43 PM
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Yeah, you're real close if not already there.
You might try one lighter spring, to see if you can get the total curve in at a little earlier rpm like you want and still not have it move motre than a degree below 1000 rpm. springs don't have to be in matched pairs, so try a heavy/medium or heavy/light combo and see if it gets you what you want.

Looks like right now your vacuum advance is adding 10 roughly??
You'll probably want that up around 15 if the engine proves it will take it without ping out on the road. You'll get the best mileage with it closer to as high as it will take without ping on mild acceleration or hot days.
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  #116 (permalink)  
Old 05-25-2019, 06:22 PM
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Here's a neat trick for leveling the RPM changes as you shift in and out of gear with an automatic transmission, it's very easy to do and costs very little;
Attached Files
File Type: pdf vacuum advance trick #2.pdf (859.2 KB, 18 views)
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