Horrible idle

[knocker]

I'm now at my wits end with my divvy 600. Since xmas it's had a really lumpy idle, when sat at traffic lights it sounds like it's dropping a cylinder and the rev counter is jumping up and down. On opening the throttle there is a bit of hesitiation before the revs pick up but then it's fine.

Also when i first got the bike it had a definite kick at about 7000 revs all the way upto the redline but this seems to have gone at the same time as the crappy idle started and to be honest i miss it. I could deal with the idle problem if only i could have my powerband back

Anyway i've cleaned the carbs, cleaned them again and cleaned them again, i've set the idle screws as per haynes, i've replaced the spark plugs, i've tried redex in the fuel. Just bought a doodah to balance the carbs but I really can't think of anything else to do to get rid of this problem.

Please - someone must know where my powerband went (and why my idle is so pants)

[metalforever]

have you altered the fueling in anyway recently? such as changed an exhaust or air filter? it almost sounds like its overfueling a little, which could also explain the poor powerband (If a divvy can be considered to have such a thing!)

I'd be checking the colour of my plugs first and then depending on that my float heights!

[cam7777]

Sounds like you have 'lost' a cylinder.
Take out the plugs and see if you have a decent spark.

[CD]

The ignition system and potential air leaks are not mentioned.
It might be a mechanically duff cylinder or it could ber a duff coil or plug lead. It could also be an air leak somewhere between a carb and the engine. This will make the engine run weak at idle. When compensated for by adjusting the mixture, the engine then runs rich.

To rule out something nasty - do a compression test. If that's ok test the coils and spark plugs. Last of all go over the carbs (including the chokes) with a fine toothed comb.

[knocker]

Its definatley running on all 4 cylinders when it's been ridden it just appears to lose a cylinder for a moment now and again when it's idling.

The plugs are sooted up but I think this has a lot to do with the fact that i use the bike for commuting everyday and therefore lots of stopping and starting a pootling about.

The carb rubbers could be letting in a bit of air as they are starting to look a bit aged and do have some cracks on the outside although I have had a closer look and none of the cracks go right through the rubbers.

Not tested the coils but will get on with that at the weekend as it's a quick job. Spark plugs are relatively new.

[CD]

Another thought... are there any vacuum take-offs that could be sucking air? The fuel tap or a badly fitted scot oiler or a loose/leaking carb balance screw.

When its idling the wonky cylinder should have a cooler exhaust pipe. If its weak when started from cold that one will be cold. If its rich that one will be cool(er) when engine is hot.

The choke plungers can also be a pain - are they all moving and seating properly.