Cylinder 1 not firing on tickover

[Wozza]

Hey guys,
Had this problem with the bike since I bought it nearly two years ago - at tickover cylinder 1 does not fire. It starts to fire as the revs pick up, I think around 2-3k rpm.

What I've done:
Spark plugs - replaced as soon as I got the bike.
Carbs - last balanced about 1 year ago. Recently stripped and cleaned, pilot screws reset, float heights reset generously, main jets upsized.
Engine - replaced recently due to a loud rattling. Replacement engine complete with new iridium plugs.

After all this the problem remains. I've checked the spark at tickover and it looks fine. I'm thinking it must be something still wrong with the carb, or possibly an air leak, but I'm fairly sure my inlet rubbers are airtight.

I won't be home to fidle with the bike for about 5 weeks, but any suggestions to get me thinking would be most appreciated.
Cheers,
Wozza

[c7ll]

Try swapping over the coils.

Trace the HT lead back from the spark plug to the coil and then swap this with another one of the coils if this shifts the non firing problem to another cylinder then you know what to replace.

Failing that corroded earths can sometimes cause firing issues.

C

[Wozza]

But the spark looks fine, is that still a possibility?

[Cammo]

Sounds like a carb issue.

I would suggest adjusting the pilot screws to make sure the idle mixture is correct, but sounds like you've already tried that.

There's a possibility that an idle passageway could be blocked not allowing fuel through at idle. Best solution for that is ultrasonic cleaning but you'd need to strip the individual carb down.

You could also try some carb cleaner in the fuel (from a reputable brand, most are snake oil!), my pick would be Motul efi system/injector cleaner.