HELP!...need timing help! - Pontiac GTO Forum
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post #1 of 31 (permalink) Old 03-29-2017, 08:14 PM Thread Starter
 
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HELP!...need timing help!

If anyone can figure this out, this group can! PLEASE forgive my lack of knowledge in this subject as I've only set 8-10 degrees on most engines with the vacuum plugged off. I've built many, many engines (mostly Chevrolet) but never set total timing on any of them. I've never understood it but never took the time to "learn". Fast forward to the last two weeks and I WANT to know total timing. I read every forum until I'm blue in the face. I print out Lars timing procedures as well as Rocky Rotella's. I buy a the Moroso 72310 advance kit (based of off Rocky's reviews and to have on hand just in case) and buy a new adjustable timing light with RPM readout (kinda nice actually).
I unplug my vacuum advance and cap it at the carb.

Start the car and let it warm up. I hit the light on and I'm showing 19 degrees at idle. (?)... 30 degrees at 2k and 40 degrees at 3600 rpm. It just keeps rising and I never did continue with seeing where total timing came in. I should have stopped there.
Due to the advance climbing past 3600 rpms, I change out the distributor springs from stock to the Moroso silver (lightweight). Bolt everything back and hit the timing light to it....30 degrees @ 830 rpms and the total timing peaked at 2600 rpms with 36 degrees set. I know none of this means a lick without my numbers being proper at idle but...?

Another thing I noticed....at 3600 rpm, the balancer mark jumps back and forth slightly (plus/minus 4 degrees). I would think that would stay right still without fluctuations.

My timing gun lead is on #1 ...why is this so off so much on initial timing? I change my timing lights to my old adjustable Craftsman and it reads the same. I am at a loss as the car drives beautiful! It had a tendency last summer to get warm in traffic, hence the crash course in timing and the jump into a part that I've always shyed away from (total timing).

Please don't destroy me with 'you're-an-idiot' comments but help me get a clue into what is going on! Thanks everyone!!!

This is a rebuilt (maybe 400 miles on it) stock '67 400 Pontiac with an 068 cam, points distributor (new stock replacement) with Petronix installed.
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post #2 of 31 (permalink) Old 03-29-2017, 08:54 PM
 
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"...40 degrees at 3600 rpm. It just keeps rising and I never did continue with seeing where total timing came in...
Due to the advance climbing past 3600 rpms, I change out the distributor springs from stock to the Moroso silver (lightweight). Bolt everything back and hit the timing light to it....30 degrees @ 830 rpms and the total timing peaked at 2600 rpms with 36 degrees set..."


Yeah, I can see why you'd be puzzled. I can't see any reason why using lighter springs would decrease your total mechanical advance. I did read that you should never use the lightest springs that come in those spring assortments. You can experiment with the others. Some say they used one stock spring, and one of the kit springs, to get their desired advance curve.

But, I can say I think 30 degrees is too much advance @ 830 rpm. Most seem to like somewhere between 12 & 18 degrees, at idle, then begin to increase above 1000, with all the mechanical being in by 3000 or a bit less. Most(but not all) engines seem to like around 34-36 degrees total mechanical advance.

I've read that some dist, especially the HEI, can seem to be through advancing, but then advance a little more as rpm increase. Sometimes this can be caused by worn advance weight pivot posts, among other things.

If when the initial advance is where you want it, the total is too high, you can install a positive advance stop of some kind, which will limit the amount the advance weights can increase timing. I made a stop for my HEI with just a simple screw, in one of the extra holes in the bar which the rotor attaches to. There are several ways to make stops.

Hey, good luck with your tuning ! Maybe some of these other guys can help solve your problem.
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post #3 of 31 (permalink) Old 03-30-2017, 05:59 AM Thread Starter
 
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Thanks BigD. I will change out the light springs and experiment around with all in at 3500. I'm guessing the new initial timing is due to the mechanical advance having those light springs and advancing early. But...is it normal for initial timing to be at 19 degrees? Seems awfully high in comparison to my past cars (8-10 initial).
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post #4 of 31 (permalink) Old 03-30-2017, 08:15 AM
 
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lil65,..I think you are doing pretty good don't be so hard on yourself....

1) base timing you set with your hand at timing mark,.... fixed
2) Centrifigal from weights RPM dependent
3) vacumn from vac can

OK so you say you got 36 total, what was base and what was centifigal?

you want to find centrifigal and it can be reduced by turning the points dist upside down on the workbench and lookin at the little slot that moves back and forth when you move the weights....

a brass collar on that pin usually in the curve kit will reduce it.

so say you have 24 centrifigal....then set base with your hand to 12...total 36

if you have 26 centrifigal set base to ten.....

if you have 30 or 32 centrifigal, then reduce it with the brass collar.

once that set, you can use a silver and blue spring to get your curve in say to 3000 to 36....

get a B26 vacumn can auto parts store; a BWD 375..... would work, and then get a vacumn corrector from Lars.....put that can in and the corrector ...

google...."How to optimize the centrifugal advance in Pontiac"....

you can then check your centrifigal advance with a protractor.....

make sure to connect your vac advance to full manifold vac so you are getting 20 to 22 advance at idle with vac connected after all said and done..

that will give you 46 to 48 timing at light throttle cruise.....smooth and run cool....

I put dist on my Sun Dist macjine, they are all off even new out of the box ones..... not unusal to see 32 degrees even more on centrifigal...from wear. and some were set that way from factory to have 32 and set timing at 4 degrees...ggreat for emissions, bad for driving!

good luck you will get it!
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post #5 of 31 (permalink) Old 03-30-2017, 10:15 AM Thread Starter
 
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Thanks Lemans guy. They say this isn't rocket science but there most definitely is a science to it!
I thought you achieved 36 total through total timing and combo of advance springs and didn't concern yourself with initial timing after that. I will keep at it and see what I can do tonight!
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post #6 of 31 (permalink) Old 03-30-2017, 11:24 AM
 
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it is confusing......

here is how I do it....forget the springs in this early part....

I find the most critical unknown......"Total Centrifigal advance"....

once you know that, you subtract that number,....say 26 from 36 to get your base setting number....you set base with your hand....

in this example 10...........................then .....26 + 10 = 36 Total timing.

Total timing is really shorthand for "Total Mechanical Timing" that is

Base + Centrifigal....vacumn advance is not considered part of it.....

with your timing light, you can do this....

vac removed and plugged set base timing to 10....

turn off car...

remove dist cap and take off one spring, replace cap...

hook up timing light....start car and rev up to timing stops...

it will come in early with one spring....say before 3500 rpm's or so....

now subtract your 10 base, and what you have is your centrifigal....the starting point...

so if you got 40......-10.....your centrifigal was 30.....you adjust that down with the brass collar.....

don't forgret to replace the spring......

springs do not effect total advance, only the rate it comes in....
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post #7 of 31 (permalink) Old 03-30-2017, 12:21 PM Thread Starter
 
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Thank you! I will post results of how I make out tonight...
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post #8 of 31 (permalink) Old 03-30-2017, 05:30 PM Thread Starter
 
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OK...Good changes here!

I immediately pulled out the lightweight springs (which were actually gold in color) and the stock weights. I then replaced them with the Moroso weights and went to the medium springs (silver). This is what I got:
8 degrees @ 750 rpm
15 degrees @ 1500 rpm
19 degrees @ 2000 rpm
24 degrees @ 2500 rpm
27 degrees @ 3000 rpm
30 degrees @ 3500 rpm

I am guessing that my weights were sticking or binding? I went from 19 degrees at idle to 8 degrees after changing the weights.

I then removed 1 medium spring (silver) and installed 1 light spring (gold). This is what I got:
8 degrees @ 750 rpm
18 degrees @ 1500 rpm
22 degrees @ 2000 rpm
27 degrees @ 2500 rpm
30 degrees @ 3000 rpm
33 degrees @ 3500 rpm

I then adjusted the distributor, at idle, from 8 degrees to 10 degrees and this gave me 38 degrees at 3500 rpm. I also noticed that my vacuum gauge was registering 15....I've never known either of my Pontiac engines to register that high. Woohoo.

Do these numbers look acceptable or should I be trying something/changing something else?

Thanks again!
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post #9 of 31 (permalink) Old 03-30-2017, 07:10 PM
 
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That is improvement,...so it appears you have Centrifigal advance of 28 degrees.....you should set your base then to 8 to give you 36 total. You can try 38.... but you have to make sure you have no spark knock. I would go with 36......8. + 28...

Your spring curve looks fine, that will really make the car run good and you have a smooth curve. Other guys try to get it lower, but you can get spark knock through the range at different RPM's if you want to spend hours doing that. I would leave it there.

Next I would get rid of the vac can that came with the distributor, get A BWD 375 marked on the can B26. That has a tattoo vac timing of 16....still too much. So email Lars and get one of his Vacumn correctors, put the B26 and the Vacumn corrector in. It limits it to 10 to 12 advance from vac.

You will then have 46 to 48 at light throttle cruise, perfect for today's gas.

So 8 Base,....28 Centrifigal = 36 total mechanical. 10 to 12 more from the vac as described....46 48

The light springs bring you all in by 3500.

Lastly make sure you hook Dist vac to Full manifold vac,....that way you will get 8 Base and 10 to 12 vac advance at idle.....18 to 20....

That will give you great idle cooling, 8 degrees won't and that is what you will have if you use ported vac.....

Nice work....you will notice the difference especially when you barely touch the gas to go,....try light pedal gradual acceleration....really nice fast and smooth....

Timing is everything!
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post #10 of 31 (permalink) Old 03-30-2017, 07:25 PM
 
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Ps 65,.... make sure you don't confuse your springs with total Centrifigal advance........

For example you could have 36 total at 3500, but if it went up as you go to 5k or 6k, .....then 36 is not total Centrifigal.....

Total Centrifigal is when the weights stop advancing, minus the base setting. If you are sure that is 28....you said it was 38 when you had Base at 10......then that is the end...no spring will make it go past 28....it is the end.....

The springs then just determine how fast it gets to the end,.....say it gets there at 3500.

Also two silver springs and all in at 3000 would be a great curve. I would use that first, and as long as no knocking would prefer it....

Either spring combination will work as long as total is right,...total is critical.....so make sure that it stops, I outlined a way to do that in earlier post

Good work, you will really appreciate it when you are driving, better gas mileage more power, better cooling, better throttle response....
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