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General => Douglas Motorcycles - General Discussion => Topic started by: runmark on 05 Feb 2016 at 20:49

Title: 2 3/4 hp ignition timing
Post by: runmark on 05 Feb 2016 at 20:49
What is the full advance ignition timing for a 1924 2 3/4 hp.  Either degrees btdc or distance btdc. Thanks, Mark
Title: Re: 2 3/4 hp ignition timing
Post by: Doug on 07 Feb 2016 at 02:34
Mark,

From the handbook (1925 edition) the magneto timing instructions are:

"Turn the flywheel around until the exact moment of closing of the exhaust valve of either cylinder is reached. The piston should then be at the outward end of the stroke. ... When the rear valve just closes the front cylinder is at the firing point, and vice versa, and the following instructions are given assuming the timing is effected when the rear valve closes (i.e. one is timing the spark for front cylinder). Place the magneto advance lever midway between full advance and full retard and turn the magneto driving wheel until the contacts are just separating, by the fiber tip just striking the upper steel segment on contact breaker. The gear can then be meshed and the magneto secured. When the spark is correctly timed for one cylinder it is correctly timed for both."


Present day riders of 2-3/4hp models may be able to offer conversion into a degrees BTDC method.

-Doug
Title: Re: 2 3/4 hp ignition timing
Post by: graeme on 07 Feb 2016 at 05:27
35 degrees BTDC at full advance is a good starting point
Title: Re: 2 3/4 hp ignition timing
Post by: Ian on 08 Feb 2016 at 01:58
The book method has always worked for me. However a key issue seems to be whether the points open the same gap on both sides - so check that and shim as necessary