How do I reduce total timing? - Team Camaro Tech
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post #1 of 14 (permalink) Old Mar 18th, 08, 05:57 PM Thread Starter
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How do I reduce total timing?

My timing is set properly but when I connect vac can, my total goes from 34* to 40 or 50 plus. The carb is an edel and I'm connecting hose to one of the two only ports on the front of carb, above throttle plates. At idle, hose disconected timing is 14*, connect hose, goes to 18*. Then rev engine and it goes sky high!
Do I need another vac can?

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post #2 of 14 (permalink) Old Mar 18th, 08, 06:47 PM
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Re: How do I reduce total timing?

That's what it's supposed to do.

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post #3 of 14 (permalink) Old Mar 18th, 08, 06:49 PM
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Re: How do I reduce total timing?

It won't be that high under load because vac is nil.

And at idle your centrifugal isn't in.

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post #4 of 14 (permalink) Old Mar 18th, 08, 06:54 PM
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Re: How do I reduce total timing?

And you want it on un-ported vac so your eng idles cooler, and lets your butterflies be further shut for the same idle speed.

Do a search on JohnZ and vacuum advance 101. It's mind altering.

That or run locked out timing and say taheck with stuff that moves around.

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post #5 of 14 (permalink) Old Mar 18th, 08, 06:59 PM Thread Starter
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Re: How do I reduce total timing?

Quote:
Originally Posted by 77wolf10.85 View Post
And you want it on un-ported vac so your eng idles cooler, and gets you a good bit more power at part throttle.

Do a search on JohnZ and vacuum advance 101. It's mind altering.

That or run locked out timing and say taheck with stuff that moves around.
Thanks Tim. So it wont go to 50* under load at 6k rpm? I'll Take your word for it. If it blows, I'm commin to get wolf's zz4 engine

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post #6 of 14 (permalink) Old Mar 18th, 08, 07:07 PM
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Re: How do I reduce total timing?

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Originally Posted by speedfreek View Post
Thanks Tim. So it wont go to 50* under load at 6k rpm? I'll Take your word for it. If it blows, I'm commin to get your zz4 engine

My zz is locked out

As load goes up, butterflies go open and atmospheric pressure fills the intake(manifold pressure rises aka vacuum decreases)

Your first post told me your butterflies are too open, on ported at idle if connecting the hose got you 4 more degrees. At correct idle position your ported vac should be above the bfly.

Leave the base at 14ish, stick the can to unported and then slow your bfly down about a ****load. Then tweak idle jets, back and forth a few times idle speed/idle jets. Put a vac gauge on it or listen for lean drop and give it a quarter rich per screw from lean drop.

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post #7 of 14 (permalink) Old Mar 18th, 08, 07:12 PM
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Re: How do I reduce total timing?

Then to tell if you have it set just barely rich grab your brake booster hose and pull it off while you have it pinched shut with your fingers. Then just barely let it suck air, the engine should speed up a little telling you you had surplus fuel. As you open it to air more... the engine should get puny.... if it continues to speed up you are set waytaheck too rich. It's one of those deals you have to play with a few times, and some engines are too finnicky to find a real sweet spot .

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post #8 of 14 (permalink) Old Mar 18th, 08, 08:24 PM
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Re: How do I reduce total timing?

Quote:
Originally Posted by 77wolf10.85 View Post
And you want it on un-ported vac so your eng idles cooler, and lets your butterflies be further shut for the same idle speed.

Do a search on JohnZ and vacuum advance 101. It's mind altering.

That or run locked out timing and say taheck with stuff that moves around.
yup!!!

lock it out..so you have around 14 at idle and 36-38 total........

Remember,I'm not making this stuff up!

1969 rs/ss 396 350hp/4spd conv a/c,pw,ps,foldown
1968 Z/28 crossram- j/l8 conv pw,ps,foldown
1963 nova ss 350/4spd conv a/c,ps,pt
1963 nova 400 4dr 6cyl/700r4 a/c
2006 GT/5spd mustang conv
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post #9 of 14 (permalink) Old Mar 19th, 08, 04:46 AM
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Re: How do I reduce total timing?

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Originally Posted by wagonman View Post
yup!!!

lock it out..so you have around 14 at idle and 36-38 total........
If it's locked, it isn't going to be like that....
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post #10 of 14 (permalink) Old Mar 19th, 08, 05:03 AM
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Re: How do I reduce total timing?

Locked out means stationary, no centrifugal or vac advance.
36 is always 36 etcetera.

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post #11 of 14 (permalink) Old Mar 19th, 08, 07:55 AM
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Re: How do I reduce total timing?

GM HEI distributors are known for advacing well into the 40* range and even up to 50*. First off, check the weight bushings to make sure they aren't worn. If they are, replace them. You can drill holes in the base-plate and insert a stop to limit the total advance. Vacuum advance changes won't help you above idle.

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post #12 of 14 (permalink) Old Mar 19th, 08, 10:30 PM
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Re: How do I reduce total timing?

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Originally Posted by onovakind67 View Post
If it's locked, it isn't going to be like that....
i see what you mean.i should have been more specific.

if he chooses to lock out the vac adv. and then re-curve his dist to get the timing specs he wants.which may be 14 at idle to 36-38 total.he would be fine.
getting even more specific he would have to know when he has all his total timing in at...

lets say 2800 rpms or so? just a general guess.

Remember,I'm not making this stuff up!

1969 rs/ss 396 350hp/4spd conv a/c,pw,ps,foldown
1968 Z/28 crossram- j/l8 conv pw,ps,foldown
1963 nova ss 350/4spd conv a/c,ps,pt
1963 nova 400 4dr 6cyl/700r4 a/c
2006 GT/5spd mustang conv
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post #13 of 14 (permalink) Old Mar 20th, 08, 04:13 AM
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Re: How do I reduce total timing?

You don't have to 'lock out' the vacuum advance, merely removing the hose will disable it.
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post #14 of 14 (permalink) Old Mar 20th, 08, 02:03 PM
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Re: How do I reduce total timing?

The acdelco servive manual for points and hei dizzys show 100s of variations...
Generally there is about 14 to 22 in the cent and 5 to 18 in in the vac advance...
The stock vac advance units have a couple numbers stamped just behind the diapham unit, one of these tells u how many degs are in it, but not the vac range

To mave both the gm pionts and hei dizy adjustable in the cent
1/ the tail shape of the weight will limit the total, if u need more, reshape the tail and shorted by about 1 to 2 mm...take too much off and the weights will fall off the plate and jam open.
you will also se a spare hole in the plate the weights sit on..tap this, then use a grub screw, with the head reshaped into a cam..find you required total note the postion of the 'cam' grub screw head..then fix in that position with locktight

2/ Vac advance...this has 2 parameters of operation
a) the amount of degrees..this is the distance the lever moves in the slot
b) the vaccuum at which it works at...this is where in the slot the lever moves
Extend the slot if needed...then make 2 little stop plates out of a bit of thin panel steel...
you can have each with 3 or 4 little 'v' s where the lever hits so each has several choices of distace to select
These mount at each end of the vac advance mounting screws

You now have a truely fully adjustable dizzy and vac advance
A note on after market adjustable vac advance units with the screw inside...you will have a starting point range (for example) about 5 to 12" of vaccuum and maybe 10 degrees, as you adjust the screw, the vac range will go to about 10.5 to 12" of vac and the deg will reduce to about 3"
Not all adjustable aftermarket vac advace units are the same spec but the example above still remains

My Spelling is not incorrect...it is creative

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