New conumdrem puzzle

Engine only runs on three cylinders

Front left and right fire,rear right fire but left rear nothing.
Things checked to date cylinder cold,loads of compression and new plugs.

Fuel in carbs OK
Ht coil pack replaced Not firing
Both spark packs replaced Not firing

One possible culprit
The ignition switch is intermittent on the side lights ( you have to wiggle the key to get them to turn on)
Have now ordered a new ignition switch just in case it is not allowing enough amp-age to one spark pack so its only able to spark on one side of the coil pack due to resistance

this is pointing to a bad connection

Odd cos the ignition is shared between two cylinders so if only one is out it has to be an HT lead. Hope that helps…

I replaced both ht leads and caps but still not firing
definitely not sparking at plug I pulled them out

strange fault its just not logical

will have to check the earth’s on the frame

hi windy,try crossing the rear leads over at the coil to see if it sparks on the left cylinder,

you could even try plugging both rear HT leads into the front coil and see if you get both sparking, if you do still get one spark it will indicate faulty plug or lead.

may be worth checking the gap between the pulse generator and the starter clutch, not sure how critical this is or weather it could cause a week spark or not.

just a thought, was the bike running ok before you changed the plugs.


now I think of it when I discovered it a day or two ago I touched the generator output wires to the rectifier and they where close to melting hot to the touch I turned it off straight away.

must investigate why ?