New problem

[fido]

Buy what you like, but points being old does not make the spark disappear. Nor do brushes of different lengths. If you disturbed the points and had no more spark, you may have made the spring short out, or got grease between the points. You may have let an HT brush fall out of the pickup. Is the earth brush (or brushes) in place?

It's hard to think of something that would cause a good running bike to start pinking. Why would the timing advance itself? Timing slips, but usually goes retarded. Pinking can be caused by weak mixture, as said above. A mixture which becomes weak in service can be caused by a manifold air leak. Test by spraying WD40 at the joints in the manifold while it's idling.

As someone mentioned, too much coke in the combustion chamber can cause pinking. Not a common problem nowadays.  

Sounds like something is fouling your plugs, if new plugs help for a while. Blocked air filter causing richness and sooting of the plugs?  Did the bike start smoking?

If the mixture is too rich it can't be the mixture that's causing the pinking so there would have to be 2 faults i.e. timing advanced AND rich mixture, which seems unlikely.

[Triton Thrasher]

Yes. I'm puzzled.

[Pecon]

I am going through a process of elimination with the points and brushes but I also have carb problems as it seems to be drawing air from somewhwere. I have tried spraying the joints as suggested but no sign of anything amiss. The carb is a 276 (running without a filter) which was recently overhauled but has run rich since even when I reduced the needle jet. The engine has just 600 miles on it since a rebore so carbon is an unlikely cause of the problems. Cold starting is my main problem, once warm it's a first kick starter(at least it was up to now). Frustrating to say the least..!!.

[wilko]

The pinhole for the idle circuit is probably blocked. Drop the jet block out and start probing.

[Triton Thrasher]

Might sound silly, but people being scared to tickle the carb enough can seem like a real cold starting problem.

[Pecon]

Just a quick update. The points and brushes arrived from Bright Sparks this morning. The bike is now starting first kick hot or cold which it never has in the past, an amazing difference..!!. I spoke to the guy who sold me the bike and it turned out that he replaced one of the brushes after breaking one. So that accounts for the odd sized set. I'm not sure if the problem was with the points or the brushes but in any case it seems to have given the machine a new lease of life. Thanks to all who took the time to reply to my plea for help.

Peter