DuncanC

Hi,


First of all my bikes a 2000s.
A couple of weeks ago I was out and about when having pulled away from a junction I revved it up to the red line and it cut on to one pot. Due to missing allen keys I couldn't do much with it so ended up limping home on one. As I was limping along I noticed that when I closed the throttle it was popping and banging burning fuel in the exhaust.
When home I checked which pipe was hot and determined that the rear cylinder was the dead one.


Next morning I checked the plug cap was on, pulled the plug (a couple of thousand mile old iridium number) and checked all the connections a round the coil. Nothing was wrong. So I fired her up and went for a 30 mile test ride. She was fine I tried high revs chugging along at low revs all was well.


Fast forward to yesterday I went for another blat. I noticed that after a couple runs up to the red line she was reluctant to rev past 7500. Fine up to there no matter what throttle I used but not revving past 7500/8000.
My tacho is an after market one that uses pulses from the rear coil (easier to get to) I noticed that it started fluctuating when misfiring, several hundred revs either way, so not reflecting the engine speed.


I'm now wondering is the tacho fluctuation caused by a lack of voltage to the low tension side of the coil or would a lack of spark cause there to be no signal from the coil?
If the former is it likely that one signal from the ignition box could break down under load/ when hot?
If the later can I change the HT lead on this type of coil or are they moulded in?
Any other idea about what might cause this sort of thing?
Thanks for your help.