Topic: cb550 part throttle carb problems

[philgresty]

Hey guys
I have a cb550f, it is running k&n filters, i bought it with them, have since gone over the whole bike (valve clearences. carb sync, timing etc) and it is running great, accelerates up to 90 easy, with no hassle. the problem is when i'm cruising on the motorway about 50-60 mph at part throttle, the bike feels like its struggling to stay at that speed. But if i give it wide open, it will get past it until im at part throttle again.
Part throttle below 45mph there is no problem
will changing the needle position solve it?
Hopefully someone can help
Thanks in advance
Phil

[jonda500]

If the needle clips are still in the standard #2 slots (2nd from the top), I reckon moving them to #3 slots (middle position) would be worth a try (then you'll need to vacuum synchronise the carbs). Have you checked what size pilots and mains are in there?
John

[calj737]

Before you jump to conclusions on your carb jetting, you might also verify some other aspects of the bike, like sprockets, ignition timing, and plug colors. When cruising at 50-60, what gear and RPM range are you experiencing? Its possible you're "lugging" the motor and no engine enjoys that nor responds well in that state.

If your K&N filters are "pods", then you very likely have some carb tuning issues ahead of you, and flat spots are indicative of that effort. But do verify and confirm other aspects also. And before changing needle positions, plug chops are a must.