The bike was running rough and could not get a constant idle speed. I checked the air filter and it was pretty well shot (contamination, etc.). As I awaited delivery of the new air filter, as a test I ran the bike without the air filter and it had instantaneous throttle response and constant idle speed. Great!
I fitted the new air filter and the throttle response was good but the idle speed was totally erratic. It was OK at 3000 revs but anywhere below that it would run a bit and then drop down and stall.
The plugs, etc. are all good, just this idle speed. Is the petrol feed on a vacuum and not getting proper mix?
Can anyone advise and help, please?