Setting Ignition Timing

General discussion about our beloved Tercel 4WD cars
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Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Setting Ignition Timing

Post by Phatcat »

Hey, JJ here again. I’m doing some work on the Tercel tomorrow and need to check the timing to be sure we have it in the right place. I’m in the process of reading about and learning this car/ 3-AC motor. My Tercel has three vacuum lines going to the distributor. I have access to the online manual of course (I prefer paper in hand though), but the drawings are a bit confusing to me, admittedly. Bottom line, factory setting is 5 degrees btdc yet advice from folks is to have it set at 10 degrees btdc with the “correct” vacuum line(s) removed, and capped off on the lines for no vacuum leaks etc, right? So which vacuum line(s) do I need to remove precisely? Which one is vacuum advance and high altitude etc? A description of what each line does would be helpful. I’m sure the service manual pictures will make sense once I know what I’m doing better.
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dlb
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Re: Setting Ignition Timing

Post by dlb »

The bottom vacuum advance port advances the timing during highway cruising.

The upper port (with a normal hole) advances the timing during both highway cruising and idle -- this is the one that needs to be plugged when setting the timing.

The upper port with the tiny hole goes to the high altitude compensator.

5-10 degrees BTDC is fine, everyone has an opinion but anywhere in that range is fine (as long as the engine doesn't ping when warm and under load) so just go with whatever you prefer. :)
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Petros
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Re: Setting Ignition Timing

Post by Petros »

the 5 deg BTDC setting was an emissions driven specification. It reduces peak pressures and temperatures during combustion, at the cost of peak power output and fuel economy, and possible risks severe engine damage when the exhaust valve overheats and breaks off.

All of the fuel is not fully burned at 5 deg BTC, at 10 or 12 deg advance, all of the mixture fully burns before the exhaust valve opens, so the exhaust gases are cooler. I have had, and have seen a lot of other Tercel engines get severely damaged when one of the exhaust valves (usually on the #1 or #2 cylinder) break off from running too hot. when that happens the most likely out come is you totally trash the engine, sometimes you get luckily, and only trash the head when that happens. I mean severe engine damage. I have seen valve stems driven up through the combustion chamber, through the head and poking into the oil basins under the valve cover. it dropped on to the piston, and the piston drove it back up into the head in abut 3 milliseconds after failure. I have also seen exhaust valves fully embedded into the top of the piston, bending both the connecting rod and bending the crank shaft, as well as completely crushing the combustion chamber into the coolant passages.

I am sure it really saves the environment by slightly reducing emissions, at the cost of increasing the fuel consumption, and having the engine end up in the scrap yard too early because of premature catastrophic engine failures. Thank you EPA (that is sarcasm, governments operate with such blind stupidity and incompetence I now despise all of their actions). So I always set my timing at 10 to 12 deg BTDC, and always replace my exhaust valves when ever I have the head off for any reason (they do not cost much, and is a small cost compared to the risk of trashing the engine).

it is best to remove and cap all of the vac lines to the vacuum spark advance when setting the spark timing. Remember to get them back onto the correct port when done.

as stated above, one line is to advance the spark when at part throttle cruise to improve the economy, the other is to advance the spark at high altitude if your car is equipped with the HAC (high altitude compensator), both conditions are when the fuel air ratio is lean, and the fuel air mixture burns slower, so the advance timing improves the economy. The other one is part of the emissions system as I recall, and will retard the timing when running at full throttle as I recall, to reduce peak emissions. All the newer cars have their ECM to control these spark timing requirements, with much more precision and efficiency than these old mechanical system.

The car will run fine without any of them working if capped off, many cars before about 1974 or so had no vacuum advance at all. But your econmy may suffer slightly without them during cruise at hwy speeds, or above about 4000 ft elevation. If your vac diaphragm is ruptured you are better off just capping off the vac lines because the advance will not work anyway, and it will act like a vacuum leak.

Good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

Thanks Petros. The ruptured diaphragm may be what I’m dealing with, as when I remove any one of the three vacuum lines off the distributor the timing stays the same, at about 14-16 give er take. I’ve never had a car this difficult to see the timing marks and numbers on. I’m still working through this car. However, when flipping the throttle I can see the timing advance as it revs up and then back down. I don’t know these mechanical distributors that well. So if you have advice, I’d take some.. You may be onto something with the ruptured diaphragm. It runs okay, but something is amiss. Thanks.
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dlb
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Re: Setting Ignition Timing

Post by dlb »

It's easy to test diaphragms. Just take the end of the hose that goes to a diaphragm, wipe it clean, and suck on it. It should hold vacuum. If you can keep sucking air through it, it's ruptured. In that case plug the end of that hose until you can replace the diaphragm. This applies to all the various diaphragms: both on the vacuum advance, both on the choke breaker, the choke opener, EGR, throttle positioner, etc.

The timing #s on the timing belt cover get covered by oil and dirt, just give it a good wipe down there and you will see them. On the crank pulley, there is a very small notch on the lip closest to the engine. I always paint that notch with a tiny dab of white paint so that it's easier to spot. Just rotate the pulley clockwise using a ratchet and 17 mm socket (make sure the transmission is in neutral) until you see the notch approach the timing belt cover, then paint it. Remember to remove the ratchet when you are done!
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

I’d give an arm to have someone experienced give me a lesson on these carbs. BC Canadian dlb? Damn, I was contemplating having you give me a lesson on these carbs if you were close. We’re not too far all things considered, but far enough.. I’m a descent weekend Wrencher of 90’s Toyotas, but admittedly not carb experienced. I had an 81 pickup with the 22R and a Weber, but that was much less complicated than the emissions riddled Tercel I have now. I’ll get it figured out, but yeah… it’d be nice and probably cool to meet and have someone show me some stuff. I’ll get there from reading and watching videos.
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

Let me say what I think I know, but maybe don’t know and then we can work from there and maybe learn me something. With the vacuum advance line(s) hooked up to the dizzy, if functioning, the timing should be “advanced” 8-10 degrees btdc, with it unhooked we should be down to that 5-10 degrees btdc, when we’re all warmed up and such, right/wrong? At least, that’s how every other ignition timing setup I’ve seen works. I’d just disconnect all the vacuum lines and set it to 10 degrees and roll with it, but don’t want to punish this old engine any more than I need to without any fun involved.
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dlb
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Re: Setting Ignition Timing

Post by dlb »

Yup, you have that pretty much correct. You set your base timing, whether it's 5 or 10* BTDC, then when you hook up the hose to the upper vac advance port with the big hole your timing should advance about 8*.

The lower vac advance port will not show any advance when it's hooked up because it only receives vacuum at partial throttle (aka during highway cruising). That's why it's important to suck on the hose that goes to it and confirm that it holds vacuum. If it doesn't hold vacuum you want to plug that hose because it is a vacuum leak during highway cruising, otherwise.
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

Okay. When sucking on the upper and lower vacuum lines to the dizzy I get no resistance and can hear air noises coming from the dizzy. She ain’t holding vacuum people… well, there’s my problem… I believe you guys have helped me diagnose why my timing stays the same with/without the lines hooked in. Appreciate that.. I shoulda caught this myself 🙄 Now I need to find a new diaphragm or repair it. I’ll start looking tomorrow but let me know if you all have ideas where to snag a diaphragm or advance mabobber. I read this has been a common issue here. The boat patch idea could work, if resistant to fumes and such.. I wonder if a 22R dizzy vac advance would work. They look damn similar to me, but I have only looked at images of the 3-A diaphragm and it’s been awhile on the 22R dizzy. I’d bet other diaphragms from other models would be compatible or trimmed to work. Also, very little resistance from the lower vacuum line too. So yeah, thanks for the clear up and help. The middle vacuum port is capped off and has no lines going to it. I’m guessing we’ll just cap them at the vacuum rail and roll for awhile. I’ll find a replacement and/or way to repair it soon. Being a fisherman and hatchery specialist, the aqua seal idea is interesting and available to me for patching waders. But I doubt it would be fuel/oil vapor resistant. I may try the right stuff or some other permatex. Kinda excited to see how it runs WITHOUT vacuum leaks. A big improvement came the other night when I found a vacuum line to the charcoal canister completely melted and a definite vac leak. So this dizzy nonesense will get me close to a descent running car. This gem is way too clean to not have around. Gotta get it running better. So, the dizzy diaphragms don’t hold vacuum, I should keep the timing at about where, 10*? It’s at 14 now when at idle and warm but that’s with no diaphragm function. Thanks again dlb and others. I’m really liking this community of Wrenchers.
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

Doing some reading and came across an article using plastidip to repair old obsolete vac advance diaphragms. Hmmm? Well, I’ll post my conclusion and see what I come up with. I still think permatex rtv would be ideal for patching a few small holes.
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dlb
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Re: Setting Ignition Timing

Post by dlb »

I tried repairing vac advance diaphragms recently but failed miserably. The engine can run fine without them, lots of people disable all of that stuff, so don't sweat replacing them unless you really want to. Plugging the leaks is important though.

I would probably set the timing at 10* BTDC but basically, as long as you aren't getting any pinging when the engine is warm and under load (eg low rpm while going uphill) it's fine.
Phatcat
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My tercel:: 1984 Toyota Tercel 4WD
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Re: Setting Ignition Timing

Post by Phatcat »

Yeah, I’ve seen people modify the dizzy on the older late 70’s early 80’s 20R and 22R pickups by swapping springs out to gain more advance and slight power increase. To me, it’s a goat and will never be a “fast” vehicle without major modifications and a different ecu system. I didn’t buy a Tercel to have a race car. I’m just looking for it to run good and be a reliable fun little car. I haven’t tested yet as it got way too late. I’ll pop some caps on the vac rail and dizzy ports (just to keep crap outta there) and see how she runs here today. Thanks again.
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Petros
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Re: Setting Ignition Timing

Post by Petros »

cap off the vac lines at both ends if your vac advance will not hold a vaccum. also, check to make sure your mechanical advance is working. with the timing light watch what the timing does when you rev the engine, it should advance. if not, it is usually an easy fix, remove the distributor cap and get some penetrating lubricant on the weights at the base. you should be able to advance the rotor by hand, and it should snap back when you let go. if that does not work, it will run weak and have really poor performance.

running without a working vac advance will not affect max power output, it will run fine except you may have a slight reduction in fuel economy for at steady state hwy speeds. but without a working mechanical advance it will run weak and lack power at higher rpms, and get really poor economy.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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