# 66 gto distributor issue



## gtoearl (Dec 21, 2009)

Hi again to all, In my prior posts related to timing and tri power carb adjustment issues, your responses were helpful... Unfortunately I've become very frustrated with my attempts to correct my problem so took the car to a well known repair shop here in San Jose,ca. They discovered that my center carb was running way too lean and basically replaced jets and other parts to correct the issue. They have an old school SUN analyzer that measures the exhaust gases to get these readings. Also the rear carb had the ball and spring at the accelerator pump installed incorrectly... What's puzzling to me is that the Dist. has too much total advance... 58-60 degrees. The initial timing is at 12 and seems to run well at that point. They said a new distributor will correct that. I can buy a new one and install it myself....They also said they can rebuild mine, but it would cost more to do that. Correct me if I'm wrong here..... The total advance should be around 38 degrees. The springs in the dist. is to adjust when the timing starts to advance. IE 1400 to 2500 rpm.... There is a bushing that is on the plate and maybe that is missing or needs to have a different one to limit the total advance...??? Would an adjustable vacuum advance can, new springs and bushing, maybe new weights.....would that be the fix to get my total advance down and adjust when the advance starts to come in??? OR just buy a new distributor, Thinking of the pentronic one.. so it would appear stock... Need help guys, thanks..


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## geeteeohguy (Feb 2, 2008)

No worries. If it's a 389, base timing should be 6 degrees, not 12. Very common for the mechanical advance limit bushing (it's plastic) to crack and fall off, giving too much mechanical advance. You can replace this busing easily. I've used cut off nylon vacuum tees to make my own. Ditto for the vacuum advance limit busing....you can install a fatter bushing to limit advance, or make a stop. The adjustable vac. advance cans are junk. Search the web for vac advance limiter plates....they are available. You will have a total of about 48 degrees advance with the vacuum connected at cruise....this is normal. You want about 36 degrees total mechanical at about 3000 rpm. These old cast iron distributors last forever, and with a simple freshen up, are good to go for many more miles. Pertronics is not the answer here....Rebuilding these distributors is not difficult, and can be very rewarding. My advice is to keep the original unit and install new limit bushings and make sure the factory (stiff) advance weight springs are in place.


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## gtoearl (Dec 21, 2009)

Is there a rebuilt kit of some kind...springs and bushing, etc..?
Will the limit device that LARS has be the answer for me....?


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## BearGFR (Aug 25, 2008)

Hey Earl,
First of when checking for total advance, make sure that the vacuum hose to the vacuum advance is disconnected and plugged. The term "total advance" can be a little misleading, causing folks to think - well - _total_ must mean everything connected with all the advance you can get. It doesn't. It really means total _mechanical_ advance with the vacuum out of the picture - just like your engine is going to see at wide open throttle under load. Your engine is not making any vacuum at that point, so even with it hooked up the vacuum advance isn't going to be adding anything to the picture. It's not really possible to duplicate those same conditions with the car sitting in your driveway in neutral  -- so to get an accurate reading you have to take the vacuum out of the equation by disconnecting it. Under those conditions, you want about 36 degrees total by about 2500 rpm "or so".
But yeah, like GeeTee said, the factory spec for initial timing in these cars is 6 degrees btdc. If after setting it there you still have too much, then the way to take some out is just like you said. Put a bushing (or a larger one) on that pin that limits how much travel is possible in the mechanical advance mechanism. The old timey distributor hop up kits we used to get that came with various different weights and springs usually also included a few bushings of different sizes just for that purpose.

You might be able to get it done with the distributor in the car, but it's a lot easier to do if you just go ahead and pull it, drive out the roll pin that holds on the drive gear, and then slide shaft and all up out of the distributor body. Before you remove it from the engine, pull the cap and bump the starter over until the tip of the rotor is pointing at something you can use for a reference point, so you'll be able to reinstall it in the same position when you're done. It may take some finagling to get it to seat all the way down with the oil pump drive tang engaged because the bevel cut gears tend to move the pump a little when you pull the distributor out, so don't be surprised if you have to install it a few times to 'walk' things around back into alignment.

Bear


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## geeteeohguy (Feb 2, 2008)

Earl, yes, Lars has the stuff that you need. Also, he's a real 'go-to' guy and an expert on this stuff. Can't go wrong there.


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## Rukee (Feb 8, 2007)

Sadly, lars hasn't posted in over a year. Miss his wisdom.


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## Goat Roper (Oct 28, 2014)

geeteeohguy said:


> Earl, yes, Lars has the stuff that you need. Also, he's a real 'go-to' guy and an expert on this stuff. Can't go wrong there.


Is there a link for Lars?
I bought a period correct dist. for my '67 but it is non A.I.R and can't find one of these or any info on it.
I bought a kit for it from Ames and figured trial and error to see how it will work.
Does anyone know the difference between the A.I.R and non A.I.R?


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## geeteeohguy (Feb 2, 2008)

Yes. Google Lars Grimsrud, and all kinds of great articles come up, on Tuning For Beers and Corvette tuning. He's a very, very busy guy.


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## Goat Roper (Oct 28, 2014)

geeteeohguy said:


> Yes. Google Lars Grimsrud, and all kinds of great articles come up, on Tuning For Beers and Corvette tuning. He's a very, very busy guy.


Thanks, I found the site but it is all about Corvettes and I can't find anything on the net about A.I.R vs. non A.I.R distributors.
The Mallory replacement that was in the car has a floating vacuum advance, I have never seen this before and have no idea why it is like this.


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## Lemans guy (Oct 14, 2014)

I don't know the difference in AIR vs Non AIR dizzy......but it could be just more centrifugal advance.......

That would allow the base timing to be set at say 4btdc and then pick up the other 32 needed for total advance at the weights in the dizzy.

Why? Because retarded base timing makes your exhaust hotter and burns off the NO......same reason they used ported vac to dizzy at idle, keep the timing retarded at idle and you burn off those pollutants.....

Now anything Lars says cannot be beat, he really knows his stuff. And when you read it you will see that more initial timing and more Vacumn advance at idle gives you a cool runner with lots of pep.

You can run 6btdc like geeteeoh guy says, no problem but it will take a little more advance and run cooler too. As long as it does not ping or knock....a little more sure makes a nice ride. Each car and carb a little different so you have to try it...:thumbsup:


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## geeteeohguy (Feb 2, 2008)

GR, I _believe_ have that information on the distributors at work. The AIR was a dual diaghragm vacuum advance, IIRC. What do you need to know, specifically?


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## Goat Roper (Oct 28, 2014)

geeteeohguy said:


> GR, I _believe_ have that information on the distributors at work. The AIR was a dual diaghragm vacuum advance, IIRC. What do you need to know, specifically?


What the differences are, all I could find was a non AIR for '67 so I bought it.
The Mallory that was in it only has one hose and the VA sets on a perch and floats out when you let off and slowly returns to the perch.
I have never seen anything like this and thought maybe this is a replacement for the AIR dizzy.
I am trying to figure out if the difference is in the VA and if I can just put the AIR type on this one.
I can't find any info or pics on the net that shows or tells the difference between the two.
All I know is there are two types, one for AIR and one for non AIR but no info on the differences.
:banghead:


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## geeteeohguy (Feb 2, 2008)

Eric, I believe I have the factory diagrams at work. Will check on Monday. In the mean time, I looked in my '67 factory service manual, and found this on page 6e-31: "On AIR cars equipped with the double acting diaphragm (dual diaphragm) , the vacuum retard side of the diaphragm is connected to manifold vacuum. At idle speed, with the throttle valves closed, vacuum on this diaphragm retards the spark 10 degrees. The opposite side of the diaphragm is connected to a spark port above the throttle valves. When the throttle valves are opened, vacuum on this side of the diaphragm immediately advances spark to the initial setting". There is a photo of the distributor, with the dual-diaphragm advance can, and also a photo of the 'vacuum advance valve', but no photo of it in place on the engine. I believe my literature at work will show this. If you are running the AIR, you will need this valve, along with the correct distributor advance can, all hooked up correctly, for the system to operate as designed. I will keep you posted. 
Jeff


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## Goat Roper (Oct 28, 2014)

geeteeohguy said:


> Eric, I believe I have the factory diagrams at work. Will check on Monday. In the mean time, I looked in my '67 factory service manual, and found this on page 6e-31: "On AIR cars equipped with the double acting diaphragm (dual diaphragm) , the vacuum retard side of the diaphragm is connected to manifold vacuum. At idle speed, with the throttle valves closed, vacuum on this diaphragm retards the spark 10 degrees. The opposite side of the diaphragm is connected to a spark port above the throttle valves. When the throttle valves are opened, vacuum on this side of the diaphragm immediately advances spark to the initial setting". There is a photo of the distributor, with the dual-diaphragm advance can, and also a photo of the 'vacuum advance valve', but no photo of it in place on the engine. I believe my literature at work will show this. If you are running the AIR, you will need this valve, along with the correct distributor advance can, all hooked up correctly, for the system to operate as designed. I will keep you posted.
> Jeff


Thanks for your help on this, I looked online for a dual port advance but all I could find for replacements are the single port.
My manual is at the shop so I will check that page and see if I have that valve.


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## geeteeohguy (Feb 2, 2008)

Ok....the dist you 'need' is #1111252, and used only on the AIR cars. Weird, my book at work says only the LOW compression 8.2 AIR engines got the dual dia. distributor, but looking at the application chart, there is no AIR dist listed for the Low CR engines. In fact, no AIR system at all on those, which is strange and hard to believe. PM me with your personal email, and I will scan what info I have and email you the pages. There is some interesting stuff here.


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## geeteeohguy (Feb 2, 2008)

Goat Roper, I'll PM you........


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## Goat Roper (Oct 28, 2014)

Email addy sent.


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## gtoearl (Dec 21, 2009)

Interesting read guys.... thanks for taking advantage of my initial post... I really like reading about different issues... As for mine... The more I read the more I get confused and a bit overwhelmed with all the info... I 've been in contact with LARS and he has given me so much info I can't believe how knowledgeable one guy can be....If you guys need to contact him here is his email... [email protected] As was said in the posts, he is a very busy guy and expect a few days or so for him to get back to you.

As for my continuing issue... I took my 66 GTO tri power to a local well know auto shop here in San Jose, CA , as I was frustrated with the timing and carb idle... They basically said after putting it on a gas analyzer, it was running too lean and had to jet up the center cab idle circuit....drill sizes... main jet is now 62. Car runs very well, but I have a total advance of 58. way too much...they said to get an adjustable vac advance or buy a new HEI dist. LARS doesn't like adjustable vac cans.. also LARS indicated I may have a broken or missing advance limit bushing...haven't gotten it off the car yet to see.... 

My question for you guys is...what is the difference in all the Pontiac distributors... I don't know what # I have in the car yet...never noticed.. I do have one on the shelf with #1112145... and was running in the car a few years ago...understand it is a 1972 455 4bl distributor, didn't know know that until I looked it up on line. The 66 gto tri power dist is 1111175... should I be running this one? Is the different basically the mechanical advance in the dist? and can that be adjusted with the bushing to meat my application....And should I be aiming for a total of 36 degrees at the crank?

Sorry guys...I just noticed I talked about some of this stuff in my earlier post.....I've been reading so much stuff I 'm starting to repeat myself...LOL Or maybe it's just the age thing....

BEAR... you mentioned a HOP UP KIT in your post here..... do you know the kit #s?


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## geeteeohguy (Feb 2, 2008)

Earl, I mentioned the limit bushings and the junk adjustable advances in the 2nd post on this thread. The different dist. numbers are for different applications, and have diferently calibrated advance curves. _All _of them can be tuned to work for your car, so experimenting is just fine. You need to limit your total cruise advance to 50 degrees or less, or the car will 'trailer-hitch' when going down the road at cruise. I have limited the mechanical and vacuum advance on both of my GTO's, and it worked wonders. Again, not hard to do. Just takes some time and fiddling. A GM HEI distributor will not work with a tripower engine....too big to clear the end carb.


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## gtoearl (Dec 21, 2009)

Thanks again... I just took apart that spare dist to see how it goes together.. Not a big deal as you said.. Just picked up a Morison shim kit and Mr gasket spring and bushing kit today... Will get a reading of the initial , mechanical, and total timing of the car in a few days... I'm hoping that the dist in the car is just missing the limit bushing.


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## Goat Roper (Oct 28, 2014)

gtoearl said:


> Thanks again... I just took apart that spare dist to see how it goes together.. Not a big deal as you said.. Just picked up a Morison shim kit and Mr gasket spring and bushing kit today... Will get a reading of the initial , mechanical, and total timing of the car in a few days... I'm hoping that the dist in the car is just missing the limit bushing.


The limit bushing on the replacement dizzy I bought was missing and someone modded it by welding a bead on one end of the oval.
I filed the bead off to the original oval and pressed the bushing on the pin that came with the Mr. Gasket kit.
Same thing here, if I ever get this engine back together I will run it and do the trial and error thing when I run it.


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## 1966 GTO KID (Oct 10, 2011)

*Where is the distributor number located*

Does anyone have a picture of where the distributor number is located.
I have an original AIR 1966 GTO built at the Fremont Plant and would like to check further into this topic that is on the workbench. - Thanks!


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## Goat Roper (Oct 28, 2014)

Not sure on the '66 in '67 they changed from cast iron to aluminum and the # is stamped on the back side on the round part of the casting.


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## geeteeohguy (Feb 2, 2008)

The numbers on the older cast iron distributors are located on a red anodized aluminum band attached to the shaft. Easily lost/removed/changed. Sometimes there is also a number stamped into the body, but not often. As stated, that is more often the case with '67-up aluminum distributors.


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## gtoearl (Dec 21, 2009)

Hi everyone... I'm back at it again... Got frustrated with my tri power not running right. Took it to a local shop and they got it running pretty well. Carbs and idle good..... Only problem remaining is the total advance. They said it's around 48 to 50 degrees. To much, should be around 36 to 38. Said I needed a new dist. Thought I would either by a pentronics or rebuild mine with springs and bushing. Got nervous and bought a new oem rebuilt one from a local parts store. But I don't see a limit bushing. should there be one? I haven't installed it yet. My timing now is 6 1/2 degrees w/o vac initial. 19 degrees , jumping around a bit, w/ vac. and 29 degrees or so at 3000 rpm for, I think wide open total advance. If I add the initial w vac and the wide open advance I get the 48 degrees or so the shop said I have. Is this correct? and shouldn't it be around 36 degrees. Sorry guys, still a little confused about the whole thing. Recommendations requested! thanks....


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## PontiacJim (Dec 29, 2012)

I am no expert on this, but maybe this explanation may help.

Total timing is WITHOUT the vacuum advance connected - so this must be disconnected and the hose end plugged off. So if you want 36-38 degrees total advance, this is a combination of where you set your timing mark on the balancer at idle speed, 12 - 14 degrees. The distributor has the weights & springs that add additional timing advance as the RPM's of your engine rise - this is called your advance curve. The rate at which the advance curve kicks in is based on how much tension the springs offer that are attached to the weights. There are light, medium, and high tension springs to "tune" your distributor's mechanical advance. These springs are purchased in kit form from aftermarket suppliers. Your factory distributor is set-up by the factory and should operate as the factory specifications call for. Any modifications to your engine can change the factory specs and this is where you play around with the springs/tension to adjust the timing curve that best suits your engine -and sometimes the gas/octane you are using.

The built-in mechanical advance in the distributor for a Pontiac should be around 24 degrees. Add your initial timing at idle, 6 1/2 degrees, and you get 30 1/2 total ( you won't get 36-38 total degrees setting the balancer at 6 1/2). To get 36-38 as you say you want, then you will have to set your idle around 12-14 degrees - which may be too much and cause hard starts, or worse, pinging/detonation which will damage your engine. So, if you set your balancer timing at 8 degrees, add distributor timing of 24 degrees, you get a total advance of 32, 10 will get you 34, 12 - 36, and 14 -38. You will have to play around with this. 

Now the total advance can be made to be all in at 2,500 - 3,500 RPM's depending on the tension of the springs you use and how much movement your weights actually have. Aftermarket distributors offer more adjustments to include weight stops to dial in the mechanical advance. Factory distributors don't have this and fabrication of some kind is needed, but you have to know what you are doing.

Once you have your timing set, THEN you connect your vacuum advance and this can add up to 10-15 more degrees, but only when the car is cruising under part throttle.

Check out this website: https://www.msdperformance.com/support/set_your_timing/


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## chuckha62 (Apr 5, 2010)

As Jim says, Check total advance with the vacuum disconnected. Then reconnect the vacuum. When cruising at part throttle, the total advance can exceed 38 degrees. I've seen 48 to 50 routinely. I don't worry about it. If you're at 36-38 degrees at ~3000 RPMs without the vacuum connected, your throttle response is good and you're not overheating in traffic (an indication of not enough advance), run it and enjoy it.


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## Lemans guy (Oct 14, 2014)

Chuck, the gang is right. I was setting up a Pontiac distributor today, did my friends 65 corvette monday...it is really peppy now!

so i will attach some pics, you don't need a sun machine to do it but it is easier. So here is a rebuilt pontiac dist, centrifigal tested 30 degrees advance at the crank, this is weights only. Two much. Lots of them are like that. I used a piece of brass 7/32 hobby tubing and a hobby tubing cutter & made a bushing. The bushings in the curve kits are for racers and they take out two much advance. My bushing knocked centrifigal down to 26 degrees.just tested on my Sun machine. I will crimp it or put on a dab of glue, a c clip can work. A tip from Lars was to hit the bushing on it's side with a small hammer, a tap, which makes it snug on, as it is a little loose to start with. that makes a snug fit.

the hollow where the bearing slides was 9.6 or 9.7 mm, the bushing on the stem was 5.55mm....that gave me 26 on this distributor.

So I would set base at 10 for 36 total degrees.

next is vacumn can, hook it to full manifold vac, I just put in a B26 can which pulls 16 degree advance at crank...starts moving at 5hg all in at 13 hg,....my idle vac is 18hg and light throttle cruise about 16 hg..i have a vac gauge at dash.....so this gives me all the spark. Ifyou have vac at idle above 13 this is a great can and easy to get, Napa, oreilly etc.

this will give me 52 degrees at light throttle cruise, 36 total mechanical advance.

springs bring all advance in by 2900 RPM and starts at 800 RPM,...Idle is 550 in drive.

idle advance is then 10 base and 16 vac for 26 and it runs smooth as silk at that setting. I have an adjustable can in their now, a crane and I am going to take that out and use this other one.

main thing is read Lars timing papers and his advice on vac cans etc. If you set your cars up like he advises it will run cool and be very powerful and efficient.

you can check all that with a dial back timing light or timing tape...

Small bushing, a B26 can or one suited better, the right springs try the crane blue and silver, will get you pretty close...

Good luck some pics


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## brydell (Oct 27, 2005)

You might also consider a MSD Pro-billet Ready to Run distributor. It uses a magnetic trigger instead of points, includes a vacuum can and is maintenance free if set up properly. You can also run it with a MSD spark box, but that is not required. For originality you can substitute a black distributor cap for the red MSD cap. I run this distributor with the MSD 6AL spark box and a MSD Blaster 2 coil with MSD wires on my '65 GTO Tri-Power 389 WS. It's flawless.


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