Yet another Timing question
Thread Starter
Racer
Joined: Sep 2005
Posts: 330
Likes: 0
From: Lurkerville
Yet another Timing question
I am trying to set timing on my 79, fresh rebuild, Edelbrock top end w/mild cam, Mallory dist. I have my initial set at 12 deg, rpm @850, steady rpm but timing bounces 1-2 deg. Total timing is 30 deg @ 3000 rpm, will not go higher even with more rpm.
I have changed the curve springs from gold (curve start 400 total 1600) to silver (start 600 total 2800). I have read BarryK's post on timing, from what I read I should I just set my total to 36 deg and let initial lie where it may.
Am I thinking correctly?
I have changed the curve springs from gold (curve start 400 total 1600) to silver (start 600 total 2800). I have read BarryK's post on timing, from what I read I should I just set my total to 36 deg and let initial lie where it may.
Am I thinking correctly?
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Originally Posted by My White 79
I am trying to set timing on my 79, fresh rebuild, Edelbrock top end w/mild cam, Mallory dist. I have my initial set at 12 deg, rpm @850, steady rpm but timing bounces 1-2 deg. Total timing is 30 deg @ 3000 rpm, will not go higher even with more rpm.
I have changed the curve springs from gold (curve start 400 total 1600) to silver (start 600 total 2800). I have read BarryK's post on timing, from what I read I should I just set my total to 36 deg and let initial lie where it may.
Am I thinking correctly?
I have changed the curve springs from gold (curve start 400 total 1600) to silver (start 600 total 2800). I have read BarryK's post on timing, from what I read I should I just set my total to 36 deg and let initial lie where it may.
Am I thinking correctly?
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Something sounds weird. My stock HEI finally wore itself out last year and I replaced it with a Mallory but didn't have any issues with it. However, I did try the extra silver springs included with the Mallory and found that they were way too weak and ended up using the gold ones. Suggest that you do a quick check to ensure something isn't binding on the mechanical weights by REMOVING the springs completely and seeing if you can then get 36+ by 2500RPM (vac disconnected and vac line plugged). If not then you've found part of your problem.
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
I agree with Bob. The boucing indicated too much endplay on the distributor shaft and probably needs shimming.
distributors are one item of a car that almost always gets completely overlooked maintainancewise. Chances are that in the last 27 years NO ONE has looked at or touched the distributor for maintance - I'd say it's about time.
Take it apart (or have a shop do it for you), check for proper shaft tolerances and shim as needed to bring it to spec. check for wearing on the gears, check the advance slot bushings, etc, regrease it, etc.
Next, to answer your question directly, yes, you can simply set it for 360 total and let initial fall where it may, but that than gives you an initial timing setting of 18º (based on a current mechanical advance curve of 18º calculated by the numbers you supplied in your post of 12º setting on the initial and ending up with 30º total timing) and with a mild cam as you mentioned I personally feel, althjough others may disagree, that 18º is a bit too high - I'd shoot for 12º -14º initial with a toiotal timing of 36º.
You may be able to increase your mechanical advance by simply swapping out to a different advance bushing (smaller diameter - BUT before you change out the bushings, read the next paragraph
Next, you said you changed your springs and the mechanical advance is starting to come in at 600rpm's? You listed your idle as set at 850rpm so that means your mechanical advance is starting to come in too soon and is actually showing up a little bit in your initial timing readings too. You want to use springs that are stiff enough to not come in until ABOVE your idle speed, lets say at 1,000rpm based on your idle of 850rpm. Find springs that will allow mechanical advance to start at 1,000rpm and allow total timing all in in the range of between 2500-3000rpm.
Re-read my post or John Hinckley's paper that I referenced in my post on checking your initial timing with the rubber band to make sure you are not getting ant mechanical advance coming in at idle, if you are, once you adjust for this THAN you can recalulate exactly how much your mechanical advance curve is giving you to see if you really need to make an adjustment on that or not.
did that make sense??
once you know the mechanical is not coming in at idle, and you know the advance curve amount is correct, than set the total timing at 36º and you should be just fine (don't forgoet to check for detonation before tightening down the distributor though!)
reconnect the vacuum advance, make sure it's hooked to full manifold vacuum and enjoy cruising!
distributors are one item of a car that almost always gets completely overlooked maintainancewise. Chances are that in the last 27 years NO ONE has looked at or touched the distributor for maintance - I'd say it's about time.
Take it apart (or have a shop do it for you), check for proper shaft tolerances and shim as needed to bring it to spec. check for wearing on the gears, check the advance slot bushings, etc, regrease it, etc.
Next, to answer your question directly, yes, you can simply set it for 360 total and let initial fall where it may, but that than gives you an initial timing setting of 18º (based on a current mechanical advance curve of 18º calculated by the numbers you supplied in your post of 12º setting on the initial and ending up with 30º total timing) and with a mild cam as you mentioned I personally feel, althjough others may disagree, that 18º is a bit too high - I'd shoot for 12º -14º initial with a toiotal timing of 36º.
You may be able to increase your mechanical advance by simply swapping out to a different advance bushing (smaller diameter - BUT before you change out the bushings, read the next paragraph
Next, you said you changed your springs and the mechanical advance is starting to come in at 600rpm's? You listed your idle as set at 850rpm so that means your mechanical advance is starting to come in too soon and is actually showing up a little bit in your initial timing readings too. You want to use springs that are stiff enough to not come in until ABOVE your idle speed, lets say at 1,000rpm based on your idle of 850rpm. Find springs that will allow mechanical advance to start at 1,000rpm and allow total timing all in in the range of between 2500-3000rpm.
Re-read my post or John Hinckley's paper that I referenced in my post on checking your initial timing with the rubber band to make sure you are not getting ant mechanical advance coming in at idle, if you are, once you adjust for this THAN you can recalulate exactly how much your mechanical advance curve is giving you to see if you really need to make an adjustment on that or not.
did that make sense??
once you know the mechanical is not coming in at idle, and you know the advance curve amount is correct, than set the total timing at 36º and you should be just fine (don't forgoet to check for detonation before tightening down the distributor though!)
reconnect the vacuum advance, make sure it's hooked to full manifold vacuum and enjoy cruising!
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Before you get out your wrenches, just be sure you're not getting a momentary "glitch" in the timing light pickup that looks like the mark is moving when it really isn't. Sometimes if my pickup lead is not in the right position on the #1 plug wire, it'll miss a beat now and then and give the impression things are changing when they're not.
