barneyb32 Posted March 22 Posted March 22 I recently bought a 1991 Yamaha TDM 850 which was running poorly and had been sat a while. It’s a twin cylinder. It would start but splutter and die. The previous owner had swapped the ignition coil with a 2nd hand one and said he thought the stator was suspect. I first cleaned the carbs which were a bit manky and renewed gaskets/seals with a carb kit. started up fine but I noticed that left cylinder exhaust would be extremely hot to touch very quickly after starting (as you’d expect) and the other would barely heat at all. Confirmed no spark by pulling the plugs(new ones) and earthing off the casing. The right side no spark with left one sparking ok. I switched the plug leads so that the lead and cap previously connected to left cylinder spark plug was now connected to the right one. Started up and now the problem moved. Right side exhaust heating instantly and left not at all. I also checked that the battery was charging when running and it is so stator ok. I also swapped stator/pickup assembly with another and it made no difference - I wanted to rule out the pick up. so 2 different coils no difference 2 different stator/pickups no difference I am wondering about the spark plug caps? I had them off earlier and measured resistance- on the 20k ohm setting one was 11.82 and the other was 12.01 doesn’t seem a significant difference?? I would be interested to hear some suggestions im thinking the cdi unit is ok because in a twin don’t both ht leads spark at the same time with one spark wasted? Any thoughts/ideas welcome- I think she’ll be a nice bike once I get it sorted Quote
barneyb32 Posted March 22 Author Posted March 22 I think I’ll unscrew the caps and swap them across. If the problem switches cylinder it will point to caps if not points to leads/coil. That will be hopefully sometime tomorrow Quote
Simon Davey Posted March 22 Posted March 22 Hi @barneyb32 I'm in agreement with @curlylegend regarding leads. A chap that serviced my old bike last year, cut the ends from the leads to "refresh" them. Made a heck of a difference. Perhaps that's all you need to do? Quote
barneyb32 Posted March 23 Author Posted March 23 Thanks to both of you I will definitely try that and report back Quote
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