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Old 08-12-2010, 05:54 PM
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Symptoms of Late Ignition Timing

I've been chasing an ignition timing problem and it looks like I caused it myself. I set my advance curve up for 20 deg initial and 38 deg max. Well, I forgot some of my mechanical advance is used up at idle. I checked with my timing light and I'm only getting 30 degrees max. I'm wondering what the symptoms are for late timing. My engine sounds different than it used to and there's a bit of a hiccup up around 4000 or so that isn't right. Can late timing cause stumbles, misfires, etc.?

I'll be re-adjusting the mech advance tomorrow and hopefully I'll find out then if it fixes everything, but I was looking for more info in the meantime.

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Old 08-12-2010, 11:21 PM
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To retarted timing will give you low power, lousey emissions and excessive bore wear. to advanced will give you pinging, hot cylinder heads and other bigger problems you really don't want.
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Old 08-13-2010, 01:19 AM
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Quote:
Originally Posted by Argess
I forgot some of my mechanical advance is used up at idle.
When setting the initial timing, the mechanical advance must not be adding ANY advance. If you are aware of this, skip the following.

If the mechanical is at the cusp of coming in at your normal idle speed, this can cause the idle RPM to "hunt" and you will have a hard time getting a solid, even idle speed. So, if you find that the springs are so light that the mechanical is coming in at idle, you can replace just one spring w/a slightly heavier spring- just enough so that at idle there's no advance coming in from the mechanical.

Adding a slightly heavier spring will also affect the RPM that the total advance is all in by, so only use just enough spring to stabilize the idle (if needed) so you don't adversely affect the total.
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Old 08-13-2010, 04:43 AM
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Quote:
Originally Posted by cobalt327
When setting the initial timing, the mechanical advance must not be adding ANY advance. If you are aware of this, skip the following.

If the mechanical is at the cusp of coming in at your normal idle speed, this can cause the idle RPM to "hunt" and you will have a hard time getting a solid, even idle speed.
Yes, I am aware of this, but guess what? The idle doesn't hunt. I agree, it should be a problem, but it isn't for some reason. The springs are the stock Mallory springs....one light and one heavy, with the heavy one being a sloppy fit. I was going to change springs to make sure the advance wouldn't start until 1000 rpm as my idle is 850, but there is one advantage. During cranking, my timing is lower than idle and it's easy on the starter-motor. One disadvantage is me forgetting to allow for some of the advance used up at idle when I changed my advance range.

Once I get everything running right so I have a good baseline, I should try changing springs to see if I can get the timing to NOT advance until the engine speed is over idle. I said it does not hunt, but it may be doing so, but over such a small range, it's not apparent. However it may have something to with when I come back to idle after a hard acceleration run, the idle speed dips low once, comes back and then stays steady.

Quote:
Originally Posted by DOCTOR DC
To retarted timing will give you low power, lousey emissions and excessive bore wear. to advanced will give you pinging, hot cylinder heads and other bigger problems you really don't want.
Darn.....I should have mentioned I was familiar with engine over-heating, loss of power, etc., but that's OK. Otheres read these threads too. My concern was if late timing could cause misfires. I sort of thought that maybe as the timing was late, the cylinder pressure would be higher making igntion mnore difficult, and as the mixture is more compressed, the increased density also might make ignition more difficult......assuming the igntion system isn't a super-powerful one.

Hopefully I'll find out today. Thanks very much for the reponses. I always post ignition problems in this electrical section vs the engine forum and worry no-one comes here that will read my posts....LOL
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Old 08-13-2010, 10:00 AM
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Back again. After some re-adjustment of the distributor, everything is back to normal. No little hiccups and engine note sounds right.

It's not a huge change. 20-38 (initial-max) is good with a tiny tick during a hard run. Dropping down to 34 or 32 max is fine....probably need to time a run to see any difference between them, but at 30 or lower max timing, it's not good ...sounds bad and partial misfires.

So it looks like I'll wind up with 20-34.
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Old 10-10-2010, 09:25 PM
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timing

Run what works best for the engine, don't worry so much about #s evey engine is diff as the weight and gear ratio of every car.
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Old 10-11-2010, 06:38 AM
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Yes, I do agree. So far, 20-38 seems to work best. I do have one little click around 4500, but it might be something else, as I have some clutch problems, etc. Might even be the dual carb linkage or vacuum secondaries clicking shut as I'm not fully on the throttle. The "click" is very faint. I have to remove the oil pan for another reason, so I'll be checking bearings and cap bolt torques at the same time. Always something ....LOL.

I seem to be missing the low end torque I expect, but that is most likely due to the intake manifold I am using.

However, now that the timing is set fairly well, I should try playing with the carb mixture a bit, and basically work abck and forth between carb and ignition a bit. But overall, I'm satisfied. Once up past 2000 rpm, and definately from 2500 rpm and higher, there's more power that I can safely use with the tires I have (BFG T/As).

Thank-you for you reply.
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