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Hi,
I noticed that the shop manual says to set the idle to 300 rpm with the spark fully retarded.
I always retard the spark for starting, but I fully advance it for running.
What is the reasoning behind retarding the spark when setting the idle speed?
Thanks, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
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Joined: Dec 2001
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ChatMaster - 10,000
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ChatMaster - 10,000
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It is to insure that the spark plug fires later in the cycle and that the explosion in the cylinder isn't restricting the rising of the piston on the compression stroke, exactly like why the spark should be retarded fully in order that the ignition for the fuel doesn't "kick Back" when cranking to start.You will get a smoother idle speed of 300 to 500 RPM. Of course the engine needs an advanced spark at higher RPMS in order that the burning curve of the air fuel mixture must get a jump on the positioning of the piston at higher speeds, since the burning speed of the mixture doesn't get a lot faster as the engine speed increases. Did that help?
Life's a long winding trail, love Jesus and ride a good horse!
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Joined: Dec 2001
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Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
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I thought he said that is was to keep the mechanical advance from influencing the setting?  
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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My wife been tryin to set my idle for a long time now
I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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Joined: Apr 2006
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Thanks MrMack. Makes sense.
Cheers, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
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Joined: Jul 2010
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Shade Tree Mechanic
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Shade Tree Mechanic
Joined: Jul 2010
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Hi guys, this might have answered my question as to why my '27 seems to run rich when everything seems to be adjusted correctly. I keep getting soot on my garage floor when I first start it up. I set the timing on fully retarded when I start it up! The air/fuel is adjusted correctly!
Any thoughts?
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ChatMaster - 15,000
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ChatMaster - 15,000
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Cold starts will always produce an extra rich mixture and some incomplete combustion. As long as the spark plugs don't get black and fuzzy you should be okay.
How Sweet the roar of a Chevy four!
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Joined: Jul 2010
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Shade Tree Mechanic
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Shade Tree Mechanic
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Joined: Nov 2001
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ChatMaster - 15,000
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ChatMaster - 15,000
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If I didn't have a black floor deposit below my test engine tail pipe end, I might not have been able to be confident in telling you not to worry.
How Sweet the roar of a Chevy four!
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