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Old November 24th, 2009, 02:32 PM
randygar randygar is offline
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Default Civvy dist centrifical advance curve

Any ideas what the proper advance curve is? I've been having problems lately with backfiring and dieseling, so bought a timing light (mine back home doesn't do me much good here!), and checked the timing, thinking it might have drifted since last time I set it. It tested perfect 5 degrees at 650rpm, but for the heck of it, played with my idle speed knob...

450rpm: 0 BTDC
650rpm: 5 BTDC
800rpm: 10 BTDC
1000rpm: 15 BTDC
1200rpm: 20 BTDC
1500rpm: 25ish BTDC (off the end of the scale)
Anything higher: 27ish BTDC

That's a pretty steep advance curve... Is that normal for these, or are my springs bad? It's a civvy dist, with the vacuum advance disconnected and capped. I'd normally expect to hit 25 degrees around 3K-4K...

--Randy
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Old November 24th, 2009, 03:12 PM
randygar randygar is offline
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Actually, 450rpm is around -5 BTDC, rather retarded...

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Old November 24th, 2009, 05:55 PM
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Does that mean 5 ATDC then at 450 RPM?

I have to look but I think i saw the curve in one of my civvy books some time back...
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Old November 24th, 2009, 07:33 PM
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yes, 5 ATDC. I figured it made it clearer to use a negative than switch terms.

If the curve is right, it's the fastest advance curve I've ever seen - If it's not, I'm thinking I might need to pull it apart and make sure I don't have a broken spring. Or ignore it, as it runs pretty well.

The backfire and dieseling are getting annoying, though... when I stop, it will diesel for about ten seconds, and stopping the dieseling by letting off the clutch creates a rather impressive (and damaging to the exhaust system, from the number of new holes it's developed) backfire. Idle is set down at 450-500rpm, so that shouldn't be causing it...

--Randy
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Old November 24th, 2009, 07:56 PM
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I usually stand on the gas pedal if the motor runs on...not let the clutch out...

Ill let you know if I can find it...
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Old November 25th, 2009, 07:39 PM
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If there is a fair amount of carbon buildup on the tops of the pistons, it can cause the dieseling too. Acts like a glow plug once its good and hot.
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Old November 27th, 2009, 04:20 PM
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I have no data for you...checked the source book that i thought I had seen it in and nada...sorry.
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Old November 27th, 2009, 05:14 PM
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Thanks for checking!

--Randy
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Old November 27th, 2009, 05:41 PM
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Wish you were thanking me for a result...
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