Hey guys, my CB250 Jade is running great but one problem is niggling me. The idle when cold Okay first start choke ect ect but even if I turn it off for 30 mins, have to do the same thing as a first morning start. Is this normal? Once warmed fully idle is fine, would it be worth turning the idle up? The carbs are orginal and by the looks of it, never been off the bike. Runners are all orginal. Would new runners and a good carb clean fix this issue?
Suggest you try backing the idle mixture screws out half a turn (richen the mixture) first as having to use the choke after a 30 minutes stop sounds to be too lean.
If it looks like they've never been off the bike then the intake rubbers probably have been cracked. I'd check the air screw setting by turning it all the way in and lightly seating it, and verifying the turns with the manual first. Those intake rubbers really only have a 10-15 year life and once disturbed past that can crack and cause problems.
Murdo's on the money, richen her up a bit and see how it goes. The choke richens the mixture by restricting the flow of air (less air to same amount of fuel therefore higher fuel to air ratio). The pilot screw also richens the mixture but in a different way (by adding more fuel to the same amount of air therefore higher fuel to air ratio). So by slowly working with the pilot screws you'll replicate what the choke is doing and eventually find a happy spot where you don't need it as much. I'd probably start with 1/4 turn out on all screws (in addition to whatever they are currently set at) then see how she goes, then work to another 1/4 turn if required (meaning you've added 1/2 a turn as Murdo suggested). Messing with my FZR I found 1/2 a turn is quite a large jump, you may still end up there but nothing wrong with baby steps.
