timing a ceefer

[mossy]

can anyone help me i bought a 1965 c15 for my first project couldn,t get it started due to timing being out, [it was backfiring] it is a replaicement dizzy,[came with all the other bits] i,ve got the head off,and am trying to time it correctly before trying again .points are opening and closing o.k [with test light] but can;t fathom out when the spark should come is it just before the piston is at t.d.c. i,ve read and read rupert ratio,s book but my points seem to open at a different time each time i turn the engine over.is the dizzy naff? [its not the origional one] or does anyone know an easy way to time it. thanks.

[Goldy]

Hi mossy. If you put the bike into top gear and turn the back wheel in the normal road direction you will see when the piston is at the top (top dead centre). The timing is 1/16" before that so if you rotate the wheel slightly backwards and then forwards again until the 1/16" before position is reached. (Make sure this is on the firing stroke ie just after the inlet valve has closed). If the head is off you can do this with a depth gauge from the top of the barrel. You then need to rotate the points plate or distributor (depending on the model you have)until the points arm is just starting to go onto the cam. This used to be done with a thin piece of paper inserted into the points as it will just pull out as they open, but if you have a test lamp then all the better. If you then tighten the points screw then that is it. If you then re check the setting the points should open at exactly the same point and if they don,t then something is wrong.   I built a C15 about 20 years ago and had the same problem that you are refering to. When I re checked the timing it was different. The reason was that it was a distributor model and the drive gear had the wrong number of teeth and so it changed the timing every revolotion. As I say it was a long time ago but if I remember correctly the B40 gear fits but has different number of teeth.  So if you timing is out after you have set it you need to look at the drive. All the best Goldy.