Re: Ignition Timing

Posted by hendred on Jun 05, 2020; 8:44am
URL: http://silk-motorcycles.221.s1.nabble.com/Ignition-Timing-tp5001920p5001931.html

Engine 126, 38mm carb.  The handbook now gets confusing, it is a heavily corrected Second Issue dated May 77.
 Page C1: ignition timing 37.5 deg. BTDC with (0.2" or 5mm) added.
Page G2: 9.1 Timing.  0.3" crossed out and replaced by 5mm full advance
Page Z2: Ignition timing. 0.3" crossed out and replaced by 0.2" or 5mm  on full advance.  
The corrections have been made using a stencil.
Talking to Clive, he confirmed that the ignition advance was reduced on the bikes with the Peter Green porting which I think includes the 38mm carb. The correction to 0.2" or 5mm would seem to be correct.  It certainly goes well at a 5mm advance.  The Lumenition system when set shouldn't require adjustment however the mechanical advance could wear over time resulting in a change of timing.

The problem is 37.5 deg advance would require a 1 metre long Conrod to give a piston at 0.3" before BTDC, not really credible.  I suspect the 37.5 deg is the error as it is only given on one page, elsewhere only piston position is given.