Re: Boyer ignition problem

Posted by hendred on Nov 03, 2020; 11:10am
URL: http://silk-motorcycles.221.s1.nabble.com/Boyer-ignition-problem-tp5001882p5002066.html

Arthur
If you type Boyer into the search box you will find quite a lot on this topic from 2014.  Look for the posting on Jan 10, 2014 by Staffs (Clive Worrall).  He had exactly the same results as you found from both Boyer and Pazon systems and also ended up with the engine running backwards.  Under Special Boyer you will see George Silk had a special system made by Boyer to give a different advance curve and Boyer can supply these as a special order - need to check with Boyer if this is still the case.

There are two types of mechanical Adv/Retd units. one with two lightweight cast alloy bob weights and one with a single brass/bronze bob weight. I believe the earlier bikes had the two bob weight system.  My bike has the two weight unit and had only one spring fitted when I got the bike.  I got two springs from Andover Norton, part no. 06-8046, and they seem to work ok.  My engine goes to full advance at about 2200 rpm.

Reading some of the old Silk articles in the Scott Owners Club website, some owners removed one of the springs to improve performance. That would cause the mechanical Adv/Retd unit to get to full advance at lower rpm.  Maybe that is why my bike only had one spring fitted when I got it. My bike doesn't have a lot of torque at low engine speeds.  Until recently it was running about 3 degrees retarded and it was a dog below 4,500 rpm.  With the correct advance it is much better and is quite pleasant to ride with a lot more low engine speed torque. Just not as much low engine speed torque as a 650 four stroke twin. I found A Graham Bell's Two Stroke Performance Tuning book very helpful in getting a better understanding of timing and exhaust systems on two strokes.  My Silk has a 17 tooth gearbox sprocket as fitted from new according to the handbook.  Some bikes appear to have had  18,19 or 20 tooth sprockets.  The smaller sprocket helps with low engine speed performance but makes it feel very "busy" at speed.