1978 KZ650 C3 - Not firing on one cylinder

I freely admit to knowing f**k all about the inner workings of bike engines
so be patient here. Recently fitted new plugs and and fuel filter. Starts
well but over the weekend lost all power over about 3k rpm. It's got
steadily worse. Whipped the plugs out and one looks almost as good as new. I
changed that plug but no difference. Does it sound like a blocked carb jet
or something? Or maybe the ht lead? I've not checked either yet as i have no
garage, it's dark by the time i get home and it's stark bollock freezin out
there. Suggestions?

 

Could be a lead/cap breaking down under pressure as it were. More likely.
Could be lower compression, but less likely.
If it improves under load using some choke then I'd suspect carb to that
pot.

If it is a lead and the case of the lead/cap has broken down start it in the
dark and carefully watch the lead to that pot for sparks or tracking of
current along it, ideal in the dark as easier to see.


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Robbo
1500GL 1988 Goldwing (Rebuild in process)
BMW K100 RS 1984
"Fairly Quick" status. Silver level
BotaFOF #19. E.O.S.M 2001/2002/2003.
B.O.S.M 2003.FURSWB#1 KotL..YTC449
PM#7

 

On the fuel filter front, it was the first thing i checked when power
dropped off. It was clogged full of shit so i cleaned it out. But seeing as
it just happens to be the first cylinder to get the fuel that's affected, it
sounds like some of the shit may have made it past the filter. I'll try
emptying the float bowl and flushing some clean fuel through and get back to
ya. Cheers.