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Unread 04-23-2013, 10:58 AM   #16
John Strenk
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make sure you set the timing with the vacuum line off and plugged.

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Unread 04-23-2013, 11:01 AM   #17
82JeepCJ7
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Set your timing with a timing light, just like you would normally do. Then, put a 3/32" Allen wrench in your pocket and go for a drive.

Using the Allen wrench, turn the screw all the way out (counter clockwise)

Go for a drive. It should not ping. Keep screwing in the adjustment until you start getting ping. Then back it out one turn.
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Unread 04-23-2013, 11:11 AM   #18
firemanjim7
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Quote:
Originally Posted by 82JeepCJ7
Set your timing with a timing light, just like you would normally do. Then, put a 3/32" Allen wrench in your pocket and go for a drive.

Using the Allen wrench, turn the screw all the way out (counter clockwise)

Go for a drive. It should not ping. Keep screwing in the adjustment until you start getting ping. Then back it out one turn.
And this will help my top end power or just my ping?

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Unread 04-23-2013, 11:12 AM   #19
firemanjim7
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Quote:
Originally Posted by John Strenk
make sure you set the timing with the vacuum line off and plugged.
Yeah I do John

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Unread 04-23-2013, 11:18 AM   #20
swatson454
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Quote:
Originally Posted by firemanjim7 View Post
And this will help my top end power or just my ping?

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I really recommend getting your initial timing and curve down first. Is your "top end" done with your foot through the floor board? If so, the vacuum advance should be absent.

Once that's squared away, do as 82 said and set your vacuum advance curve for your part-throttle, lean-cruise stuff.

I have a feeling you're running ported vacuum advance. Yes? Could be part of your problem.


Shawn
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Unread 04-23-2013, 11:24 AM   #21
firemanjim7
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Quote:
Originally Posted by swatson454

I really recommend getting your initial timing and curve down first. Is your "top end" done with your foot through the floor board? If so, the vacuum advance should be absent.

Once that's squared away, do as 82 said and set your vacuum advance curve for your part-throttle, lean-cruise stuff.

I have a feeling you're running ported vacuum advance. Yes? Could be part of your problem.

Shawn
Hey Shawn I appreciate your wealth of knowledge. I know just enough to get into trouble when it comes to timing and curves. I'm running manifold vacuum off the manifold not carb. I understand the initial timing setting completely but lost you on the curve part. Thanks for the help.

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Unread 04-23-2013, 11:26 AM   #22
Matt1981CJ7
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The top-end power problem is at WOT, or close to it. I doubt adjusting the vac canister will do much for that, since there's little to no vacuum at WOT, or under any heavy load.

If the problem is timing related, it's most likely on the centrifugal side, IMO.

Jim, you should have around 30 degrees of total advance (centrifugal + initial) around 3000 RPM.

edit: I see Shawn beat me to my first point.

Matt
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Unread 04-23-2013, 11:30 AM   #23
TrebleHook
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For what it's worth....

I fought this exact same battle with the CRT HEI clone. It was absolutely infuriating. The vacuum advance is going to come ALL IN way too early. The centrifugal advance was not accurate. I was getting almost 48*+ of total advance. I actually had too much advance my DUI too. DUI sent me a different curve (weights/springs) but that eliminated the value of purchasing a DUI that was supposed to be "plug and play" with a 258. I never got it just right...

The lesson I learned: It's not just about the engine. It's about the load (hence Sean's comments on PTC and Lean). Your tires/gearing/weight etc will impact the vacuum advance because it effects the load on the engine. With my 258/Weber 38/DUI/3.73 gears and steel rims with 33x10.50 KM2s I was never able to get it just right. I even changed out the vacuum advance to one that maxed out at 10 degrees, and that was still too much at 8-10* initial when driving at Part Throttle Cruise (which is why I agree with Matt that its centrifugal related).

Mine just knocked when I tried to get both low and top end performance. If I backed off the initial timing performance to avoid the knock at PTC, overall performance suffered pretty bad.

I tried both ported and manifold vacuum (with all the corrections) and preferred manifold vacuum- although the only real benefit was a very nice smooth idle. Once you get into it and the throttle plates are opened, the two vacuums are virtually identical.

To some degree, it's a zero sum game UNLESS you do as recommended above and do all the math to make the proper corrections.

Before I get jumped here - my issues were most certainly the result of my efforts to max-out MY inline 6 beyond its capability. In the end I just went with a V8!

Good luck and keep us posted. Always learning so interested to hear your battle stories....

Cheers,
TrebleHook
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Unread 04-23-2013, 11:34 AM   #24
firemanjim7
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Quote:
Originally Posted by Matt1981CJ7
The top-end power problem is at WOT, or close to it. I doubt adjusting the vac canister will do much for that, since there's little to no vacuum at WOT, or under any heavy load.

If the problem is timing related, it's most likely on the centrifugal side, IMO.

Jim, you should have around 30 degrees of total advance (centrifugal + initial) around 3000 RPM.

edit: I see Shawn beat me to my first point.

Matt
Thanks for your help too Matt. If it is on the centrifugal side how is this adjusted? Keep in mind it's a CRT hei.

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Unread 04-23-2013, 11:43 AM   #25
firemanjim7
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Quote:
Originally Posted by TrebleHook
For what it's worth....

I fought this exact same battle with the CRT HEI clone. It was absolutely infuriating. The vacuum advance is going to come ALL IN way too early. The centrifugal advance was not accurate. I was getting almost 48*+ of total advance. I actually had too much advance my DUI too. DUI sent me a different curve (weights/springs) but that eliminated the value of purchasing a DUI that was supposed to be "plug and play" with a 258. I never got it just right...

The lesson I learned: It's not just about the engine. It's about the load (hence Sean's comments on PTC and Lean). Your tires/gearing/weight etc will impact the vacuum advance because it effects the load on the engine. With my 258/Weber 38/DUI/3.73 gears and steel rims with 33x10.50 KM2s I was never able to get it just right. I even changed out the vacuum advance to one that maxed out at 10 degrees, and that was still too much at 8-10* initial when driving at Part Throttle Cruise (which is why I agree with Matt that its centrifugal related).

Mine just knocked when I tried to get both low and top end performance. If I backed off the initial timing performance to avoid the knock at PTC, overall performance suffered pretty bad.

I tried both ported and manifold vacuum (with all the corrections) and preferred manifold vacuum- although the only real benefit was a very nice smooth idle. Once you get into it and the throttle plates are opened, the two vacuums are virtually identical.

To some degree, it's a zero sum game UNLESS you do as recommended above and do all the math to make the proper corrections.

Before I get jumped here - my issues were most certainly the result of my efforts to max-out MY inline 6 beyond its capability. In the end I just went with a V8!

Good luck and keep us posted. Always learning so interested to hear your battle stories....

Cheers,
TrebleHook
I feel your frustration Hook! I'm running the bbd carb nuttered freshly rebuilt. 31/10.50's t176 tranny gears unknown. Wasn't having issues with running 75mph prior to CRT. Now top speed is 72mph floored. Kinda crazy to me!

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Unread 04-23-2013, 11:43 AM   #26
Matt1981CJ7
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Jim,

Here's an example of an advance curve. Disregard the pink line. That's total + vac advance, and is irrelevant for this discussion.

You simply record and plot the total advance, at 200 RPM increments. The goal is a nice consistent curve that peaks out at around 30-35 degrees at 3000 RPM.

Again, this should be done with the vac advance disconnected and plugged.

Matt
advance-curve-5.jpg  
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Unread 04-23-2013, 11:45 AM   #27
TrebleHook
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Yeah...what Matt said!!!

Cheers,
TrebleHook
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Unread 04-23-2013, 11:49 AM   #28
Matt1981CJ7
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Quote:
Originally Posted by firemanjim7 View Post
Thanks for your help too Matt. If it is on the centrifugal side how is this adjusted? Keep in mind it's a CRT hei.

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The curve is adjusted by changing the springs on the centrifugal advance weights, and/or using a different slot on the advance head.

At least that's how a Duraspark dizzy works. I have no experience with HEI.

Matt
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Unread 04-23-2013, 11:54 AM   #29
firemanjim7
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Quote:
Originally Posted by Matt1981CJ7
Jim,

Here's an example of an advance curve. Disregard the pink line. That's total + vac advance, and is irrelevant for this discussion.

You simply record and plot the total advance, at 200 RPM increments. The goal is a nice consistent curve that peaks out at around 30-35 degrees at 3000 RPM.

Again, this should be done with the vac advance disconnected and plugged.

Matt
Doesn't the engine have to be under a load to get a true advance curve?

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Unread 04-23-2013, 12:01 PM   #30
Matt1981CJ7
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Quote:
Originally Posted by firemanjim7 View Post
Doesn't the engine have to be under a load to get a true advance curve?

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No. Total advance is purely mechanical, and is not based on load.

Initial timing is based on the rotation of the distributor, and centrifugal is based on RPMs. Engine load doesn't change either of those.

Matt
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