Setting the timing

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JDNightFox
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Setting the timing

Post by JDNightFox »

I have read a few places on here that people are setting the timing at 10 degrees BTDC

I read somewhere else about it being set anywhere from 10-12 degrees, and I think mine is currently set at 13 degrees. Is that too much?

How much of a difference is it between the 10 degrees and 12 degrees
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NWMO
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Re: Setting the timing

Post by NWMO »

JD,

I was running mine around or just over 10 degrees BTDC I believe. I'm sure Peter can share more experience with degrees BTDC, but most posts reference the "ear test" for pinging. If you advance too much, you will get "pinging" or detonation.

detonation

I wouldn't expect any significant difference between 10 and 12 degrees BTDC, but play with it a little and see what you prefer. I would start and 10 and bump it up a degree or two after a week or more and listen/feel for the difference.

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JDNightFox
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Re: Setting the timing

Post by JDNightFox »

Well I don’t know if 13 is too much, so if I was going to reset it I would put it back down to 10

it seems to be running good now, it was set at 13 when it was running with no vacuum advance and I didn’t have any pinging issues but it had a definite dieseling problem on shut down
JDNightFox
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Re: Setting the timing

Post by JDNightFox »

I set mine at 10 (I think) just to be safe

Still running good, it sits at about 15-ish with the vacuum connected

Adjusted the idle to 800 also
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Petros
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Re: Setting the timing

Post by Petros »

the rule is simple, you always want to run the most advance you can without getting ping.

ping or detonation you get destructive shock waves in the combustion chamber, loose power and efficiency, and hard on the metal parts, eventually causes head gasket to fail.

the furthest you can get the spark advanced without ping, means the higher the peak pressures in the compulsion chambers you will get. the higher the pressure, the more power, and the more efficient (fuel in vs. power out) it will run. when you get too much pressure build up, the fuel air mixture preignites too early, causes losses, ping, etc.

It was known that if you lower the peak pressures you will reduce some of the emissions, at the expense of efficiency of course. so the factory setting is too low, and it is harmful to the engine. when the exhaust valve opens at the end of the power stroke the fuel is still burning, very hot, and it causes the exhaust valve to get hot, and sometimes break apart, which will wreck the engine. I have seen it a number of times. more spark advance means a cooler exhaust (more energy is used up inside the combustion chamber where you want it, not going out the exhaust).

Frankly I am not so sure the emissions benefits is worth it. Consider over the life of the car if you get 32 mpg instead of 29 because of the emissions systems losses, that means you might burn almost 1000 gallons more fuel over the life of the car. How can that be good for the environment? And you consume more resources, and likely will need major engine repairs more often.
'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)
JDNightFox
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Re: Setting the timing

Post by JDNightFox »

I just completed my 400 mile drive into texas, at an average of 21mpg

Still sucks, I don't know why at this point. I fixed 5 vacuum leaks and have the advance set correctly. It still has trouble maintaining speed on the highway.
xirdneh
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Re: Setting the timing

Post by xirdneh »

did you say you rebuilt the carb?
Love those Tercell 4x4 wagons but they sure suffer from road noise.
JDNightFox
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Re: Setting the timing

Post by JDNightFox »

No it’s the original carb

And nevermind, I recalculated with the actual distance and it's 18.5mpg highway
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Petros
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Re: Setting the timing

Post by Petros »

that does suck. should be 27-30 or better. something is not correct on the engine.

Check you do not have any brakes dragging on the wheels, your tires are inflated properly. check your air filter is not plugged up. Check your APP is not leaking fuel into the vac system (pull vac line and check if it is full of fuel), if so just cap off both ends. It will run fine after it warms up.

Make sure your mechanical spark advance is working (either with a timing light, or by manually checking rotation and free play). sometimes if it is stuck it will not advance and will give poor economy and weak high speed power. While you are at it, make sure the timing is set properly (10-12 deg btdc). you might also check the timing belt is on the correct timing, I have seen this where everything check out, but still has crap economy, and timing belt was off on tooth on sprocket.

you might check compression on the engine too. that means you have worn rings if compression is bad, though there are a few things you can do to help compression without a rebuild.

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)
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