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Had my Toro up and running for the first time this year and I thought I'd check the timing while I was giving it a quick tune up. I'm having a bit of difficulty understanding what I am seeing and was wondering if you guys could help me out as it appears I have some gaps in my understanding of this.
I warmed the car up good and made sure the choke was completely off and then I adjusted the curb idle to 850 RPM to check the specs. Points were dead on at 30 degrees. I plugged the line to the vac advance, and checked the initial timing. It was about 8.5 degrees BTDC (I remember I had advanced it just a touch from factory spec of 7.5 last summer as it seemed to run much better). Then I adjusted the idle mixture screws to max vacuum/RPM. Everything seems bang on. All good so far.
So then I decided to check total mechanical timing and the vacuum advance timing and this is where I'm a bit lost. I revved the engine to about 2700 RPM and it seemed like the total mechanical timing maxed out at about 19 degrees (vacuum advance disconnected and plugged). Does 19 degrees sound like not a lot to you? It was bouncing around about half of a degree when I was watching the timing mark which, I assume, is some wear in the timing chain?
Then I decided to check the vacuum advance. At 850 RPM I started applying vacuum and around 5 "Hg I started to see movement with the timing light. I then maxed out the applied vacuum and the timing light read 31 degrees at about 22 "Hg on the Mityvac. 31 degrees seems like it's way too high to me? I have no idea if that's way off or right honestly. *edit, it just occured to me that it wouldn't be 31 as it started off with 8 so it would be 23 degrees of vacuum advance timing rather than 31. Sorry about that. I did disconnect and plug the vacuum advance earlier today and took the car for a drive......it actually didn't feel much different than when I was connected.
I did put a replacement vacuum advance canister on the car a couple years ago. I made sure to get the correct PN from SMP but I guess it's possible I have a bad one of course. Appreciate the help as always guys!
Last edited by ourkid2000; Apr 12, 2026 at 11:35 AM.
Well, a little help from Chat GPT helped me out on this one. Normally I don't play around with that too much but I was using it to help understand the timing specs. It was actually helpful as I was getting total timing and mechanical timing mixed up. It was helpful how it broke that concept down for me and the lightbulb went on, finally.
It suggested that 19 degrees of total timing was way too low for this engine and said I should look at the weights to see if they were stuck. They were indeed stuck. The bottom of the weights ride on a little round nub on the distributor and they were not moving out far enough due to the rusty crud acuumulated under the weights. I popped them off, cleaned them up with scotchbrite, and lubricated the pivot with some lithium grease. Now, when I check the total timing I'm getting 34 degrees somewhere up around 3000 RPM. That seems more like it. It didn't seem like they were THAT stuck but I guess a little movement translates into a significant amount of timing movement.
I'm still confused about the vacuum advance though. I have no idea if it's too much vacuum advance or not.
2700 rpm is not allowing you to see the total timing, that rpm level is too low. It needs to be checked at the point the mechanical advance stops, that could be over 4k rpm for a stock distributor.
2700 rpm is not allowing you to see the total timing, that rpm level is too low. It needs to be checked at the point the mechanical advance stops, that could be over 4k rpm for a stock distributor.
Bahh,
I just realized that when I checked the total timing, after cleaning the weights, that I still had the vacuum advance plugged in. It was the vacuum advance providing that extra timing that I found. Back to square one. Live and learn. Pretty annoyed with myself on this one.
I will rev it up to the higher RPM like you suggested, and this time I will ensure that I unplug the vacuum advance. Sounds like a tomorrow job......Will report back what I find.
Last edited by ourkid2000; Apr 12, 2026 at 07:05 PM.
The amount of vacuum advance should be stamped into the vacuum canister. Here’s a picture of my 24 degree canister with a home made limiter to restrict it to 10 degrees. :
The amount of vacuum advance should be stamped into the vacuum canister. Here’s a picture of my 24 degree canister with a home made limiter to restrict it to 10 degrees. :
Ahh nice! I will take a look at mine tomorrow.
How did you fine tune that thing anyway? Seems to me that testing the amount of advance in the vacuum advance system with the distributor on the car is damn near impossible because as you apply vacuum, the RPMs increase due to the timing bump and your mechanical advance starts getting introduced so you can't differentiate between them.
How did you fine tune that thing anyway? Seems to me that testing the amount of advance in the vacuum advance system with the distributor on the car is damn near impossible because as you apply vacuum, the RPMs increase due to the timing bump and your mechanical advance starts getting introduced so you can't differentiate between them.
I do the vacuum advance at a low smooth idle rpm. Measure your timing without vac adv connected, and then measure it with it connected, you may have to drop the idle speed to remove any extra mechanical advance. Subtract the difference and that tells you how much the vac canister is providing.
It’s linear. Measure the total travel, which correlates to 24 degrees. Then divide that distance by 24 to get the degrees per linear distance unit. So if the full advance distance is 0.5 inches, divide 0.5 by 24 to get 0.02 inches per degree. Then for 10 degrees, 10 times 0.02 inches equals 0.2 inches. I then moved the bar that distance from the shaft and tightened the set screws.
It’s linear. Measure the total travel, which correlates to 24 degrees. Then divide that distance by 24 to get the degrees per linear distance unit. So if the full advance distance is 0.5 inches, divide 0.5 by 24 to get 0.02 degrees per inch. Then for 10 degrees, 10 times 0.02 degrees equals 0.2 inches. I then moved the bar that distance from the shaft and tightened the set screws.
As mentioned factory timing comes in late in some distributors. The 23 degrees vacuum advance is normal, some add 30 degrees plus. Good part of the mechanical limter vs an adjustable vacuum advance is the adjustment can't fail. Some have had multiple adjustable vacuum advance units fail, I had one. It goes full advance, which is about 20 degrees. I have actually added a set screw to limit mechanical advance in the weight bar as well.
2700 rpm is not allowing you to see the total timing, that rpm level is too low. It needs to be checked at the point the mechanical advance stops, that could be over 4k rpm for a stock distributor.
Ok, I finally got back at this today.
I checked the centrifugal advance at 1200 RPM it showed 12 degrees on the light. It's got 8 initial (set at 850 RPM) in it so it was adding about 4 degrees of centrifugal timing advance. Then at 1800 RPM, it showed 17 on the light so that's 9 degrees of centrifugal advance. Seems within spec so far. Then I went to 3600 RPM and it was at 19 degrees and bouncing a bit. I couldn't bring myself to rev that thing past 3600 RPM but the centrifugal advance seems to be stuck at 19 (on the light anyway.....8 initial so 11 degrees centrifugal advance for a total of 19 mechanical advance).
I suppose it's possible my light is not correct but I did check the vacuum advance as well and it seems to be operating somewhat correctly. I had dialed down the idle speed to as low as I could get it, which was about 550 RPM and the initial timing at that RPM showed 6 degrees. I saw 23 degrees total @ 18 "Hg applied vacuum so 23-6 would be around 17 degrees of vacuum advance applied. The max RPM was about 770 so not too much centrifugal advance would have been affecting it.
I had the weights and springs off and cleaned and lightly lubricated them prior to doing all this. I'm not sure what's going on?? Any thoughts?
Oh and this time I remembered to plug the vacuum advance
Just to be clear on the details, here are the specs for my distrubutor:
It took me some time, and lots of help on here to fully understand this table. The key being the bottom section (distributor test specs) is showing distributor RPM and advance degree numbers. Everything gets multiplied by 2X (except the vacuum "Hg) when you're using crankshaft degrees.
Breaks down like this:
At 1200 crank RPM (equiv to 600 distributor RPM), I should see 0-4 degrees of centrifugal advance. 1800 crank RPM (900 distributor), 6 to 11 degrees. Finally, at 4200 crank RPM (2100 distributor) I should see 16 to 20 degrees centrifugal advance. These numbers do not include the initial timing so you have to add the initial into the totals. So at the higher RPM I should be seeing 24 to 28 degrees total on the light. In my case, however, it's a max of 19.
Vacuum advance should start advancing at 8 to 10 "Hg and add 18 degrees at 16.5 to 18.5 "Hg.
I know you guys know all about this, just wanted to show the specs I'm working with and what I expect to see vs. what I'm actually seeing.
When I was checking mine, at one point I removed the springs completely to see how much advance happened (and it happened at very low RPM). You could do that to see if it goes beyond 19.
When I was checking mine, at one point I removed the springs completely to see how much advance happened (and it happened at very low RPM). You could do that to see if it goes beyond 19.
The weights won't go flying off with no springs will they?
Good question. I think the rotor may be close enough to the tops of the posts to prevent the weights from coming off. Mine is a GM HEI so that area may be a bit different.
Maybe use the lightest springs from an advance curve kit to make sure they stay on.
I believe the wide end of the counterweight trails the rotation. I am trying to explain that the thick part comes after the pivot pin because the rotation is CCW. DON'T do it like a Chebby, its opposite.
Upfront, let me say I applaud your adherence to weights & springs & the vacuum can. I worked with all those part for decades.
And hey, if someone hits SF with a nuke, I may have to swap points back in. But let’s hope that doesn’t happen. Just to say I’m not an electronic ignition zealot.
Over the points, weights, springs & vacuum can years I either dialed back the timing to get rid of a part-throttle knock/ping, or dialed the timing up for max power and sometimes had hard starting. But I was never satisfied. I even tested 5 or 6 vacuum cans with different spring rates just to see if I could get a good combination for California “gasoline” and my ancient V8’s.
Along the way I went from points to HEI, but had pretty much the same experience as gasoline became part alcohol. The part throttle or full throttle knock persisted unless I added Xylene and Tolulene to my gas tank in gallon amounts. They raised octane, but were not cheap and a year or 3 later California outlawed them as dangerous chemicals. That may make me live longer, but I was still looking for a good distributor that provided max. power with no ping and started easily.
3-5 years back I came across Progression Ignition HEI Olds distributor. Their deal is an HEI distributor which is vacuum sensitive, but whose timing can be set by your phone + Bluetooth to create timing maps that work for your engine and your gas. I’ve installed 2 and been happy with both. Below 900 rpm, there’s no advance at all so the cars start easily. Then if you have a knock, you use your phone to tweak the timing back in the RPM range where you have a problem. The downside risk is they may disappear some day, or the software might stop working. But for the past few years, I can report that their HEI distributors have worked perfectly.
Just my 2 cents in case you’re curious about leaving 1966 Olds factory timing technology. Again applauding your commitment to stock, but if you get curious about aftermarket, here’s an opportunity.
Upfront, let me say I applaud your adherence to weights & springs & the vacuum can. I worked with all those part for decades.
And hey, if someone hits SF with a nuke, I may have to swap points back in. But let’s hope that doesn’t happen. Just to say I’m not an electronic ignition zealot.
Over the points, weights, springs & vacuum can years I either dialed back the timing to get rid of a part-throttle knock/ping, or dialed the timing up for max power and sometimes had hard starting. But I was never satisfied. I even tested 5 or 6 vacuum cans with different spring rates just to see if I could get a good combination for California “gasoline” and my ancient V8’s.
Along the way I went from points to HEI, but had pretty much the same experience as gasoline became part alcohol. The part throttle or full throttle knock persisted unless I added Xylene and Tolulene to my gas tank in gallon amounts. They raised octane, but were not cheap and a year or 3 later California outlawed them as dangerous chemicals. That may make me live longer, but I was still looking for a good distributor that provided max. power with no ping and started easily.
3-5 years back I came across Progression Ignition HEI Olds distributor. Their deal is an HEI distributor which is vacuum sensitive, but whose timing can be set by your phone + Bluetooth to create timing maps that work for your engine and your gas. I’ve installed 2 and been happy with both. Below 900 rpm, there’s no advance at all so the cars start easily. Then if you have a knock, you use your phone to tweak the timing back in the RPM range where you have a problem. The downside risk is they may disappear some day, or the software might stop working. But for the past few years, I can report that their HEI distributors have worked perfectly.
Just my 2 cents in case you’re curious about leaving 1966 Olds factory timing technology. Again applauding your commitment to stock, but if you get curious about aftermarket, here’s an opportunity.
Cheers
Chris
Thanks Chris. I know some of those systems come highly recommended but I think I'd like to stick with the points, for now at least. I really like the idea of regular old points. They keep me engaged and I like the idea of looking after them. $$ is also a factor here.
This particular problem is aggravating though and I must say I have absolutely no idea where to go with it from here.
I thought I was on to something yesterday. A couple years ago I came across a video that showed that these distributors are supposed to have a small bushing on one of the pins on the advance. The idea was to limit the maximum centrifugal advance. So, I found a roll of vinyl tubing that seemed to match and threw it on there. It struck me that perhaps this bushing may be limiting the centrifugal advance and causing the whole problem! Makes sense right?
I used a pick to pop the "bushing" off and I re-checked. Exactly the same results. Still stuck at 19 degrees on the light. It's odd, you'd think that this would have made at least some difference. That little bushing was on the pin underneath that travels in a slot.
I had the impression you like points. Carry on. As long as the spark gets to the plug on time, they're a great way to go. And amen to preserving tradition. That's a goodly chunk of what we're all doing here. I've never been an expert, but I found a combination that works for my engines & our Calfornia alcohol gas (91 Octane).
Here are my timing notes:
(Somebody's going to flame me for those initial settings, but remember that my current distributors only get that advance when the car is running >900 RPM, so it's not exactly "initial timing". I'd stick to factory for initial timing.)
The "Red Car" is my 98 convertible.
"Set Red Car initial advance to 16-18°@800 rpm, total of 32 degrees at 3000 rpm. 38-40 degrees @800 with vacuum, set idle with vacuum on to 775-800 rpm. Set Starfire initial advance between 16-18° advance at 750rpm, All in at 3000-3200 rpm.
Progression Ignitions HEI settings
Initial timing to factory 18-20° with 30-35° timing all in at 2800-3200 rpm. Timing tab is marked ||A. |||| O. |||| R.||. Each line=2 degrees. Therefore: A=+8 degrees, 0 is 0, R=-8 degrees. Mondello says its a 45 degree block, with 455 internals & pistons 30 over; JM 20/22 cam, slight lope to it. Lynn @Mondello said aim for 35 degrees total timing at 2500-3000 rpm."
My two harmonic balancers are different in the timing markers for some reason. Never have known quite why. You'll see "Mondello" aka Lynn Welfringer rebuilt my 98 engine about 20 years ago. I wish I had gone elsewhere. My Starfire runs much better with a slightly milder cam.
The Points Game
Your distributor game now is the right combination of weights, springs, and vacuum can.
When I did this with points, I found that most of the "Spring Kits" provided lighter springs for More advance at lower RPM. They never worked for me, the cars just knocked at lower RPM. So I think I stuck with the heaviest (aka latest to advance) to minimize knock. Be aware that since the weights are locked to each other, you might want to try different springs under each weight if you're looking for timing that a matched set don't provide. It's a little exotic, but the as the weights are mechanically locked to each other mechanically they spin out as a group.
Of course the weights have to move freely, so look for grooves or other wear marks/witness marks that may make timing inconsistent. These things spin every time the car runs. While they were well built, mechanical wear is expected. Whether worn or not, I might give all rotating surfaces a polish just to be sure they'll rotate freely. Can suggest #0000 steel wool with the distributor on the bench or maybe a dremel with wire wheel. Along the way I tested a homebuilt limiter and I can confirm that helped. The screw design above is close to what helped me, but looks better built than my hack.
After springs weights, or maybe as part of an overall timing experiment, test vacuum cans built for different cars. They're not expensive and may help. I wound up with a Buick vacuum can on my HEI's since the advance rate was slower. But HEI and points distriibutors are different models. Just making the point that you can look beyond big block Oldsmobile vacuum cans for other parts that fit which work differently. When I did this, I aimed at other large GM's of the mid-60's with big blocks and took me to a part that I think was made for a Buick 455. Best I ever got. I can't recommend that can since I don't know your gas and I don't know if a whole range of vacuum cans is still available. But have a look.
Next up, I learned a good deal about timing from an article you can (or at least could) find online by one Lars Grumsrud. I don't recall the title, but his name string is unique so you should be able to find it. Talk about Scandinavian. I may have a copy saved locally, but I'll be it's still on the 'net somewhere. It was cool because he dealt with points, HEI and timing theory all in 1 place. Very helpful along my timing learning path.
What little I got. Must reaffirm I'm no expert, but my cars run o.k. to great. Perhaps some of these ideas will help.
