Yamaha XT/TT 400-600 Ignition Problem
Those of you that own one of the models of Yamaha XT/TT range have more than likely experienced in the past, a CDI problem.
The most common fault; and this is from the first of the CDI models in 1982 to pretty well into 1996, (although as the models continued they had TCI systems fitted to them) and this was intermittent spark...it showed up in many frustrating ways. For example:
(a) start when cold then not restart when hot
(b) run with no power
(c) exhaust gets very hot
(d) will run OK at the bottom end but will not rev out.
Above are just some of the most common faults. There are even stories of taping the CDI box and away it goes again and this is very true.
The problem is a design fault; the manufacturers used a single sided circuit board and not through-hole plating. Through hole plating allows the components to be secured to the circuit board far more efficiently.
When the resin in the CDI heats up and expands, it will either pull on the components breaking the solder tabs, or pull the legs of components and of course as the unit cools down, they will again touch their respective pads and leads. This could carry on for as long as 6 months but would inadvertently lead to a complete failure of the ignition unit.