Horizons Unlimited - The HUBB - CBX 250: Poor performance at high speed

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CBX 250: Poor performance at high speed

My Honda CBX250 Twister which has only done 1500 miles has developed quite a bad surge in power, runs quite erratically at anything over 7000rpm and it is almost impossible to get it to exceed 70 mph. It feels almost as though it experiences fuel starvation and I have checked the fuel flow to the carb, without any success. I would like to try and fix it myself, but have avoided taking the carb off and opening it to for instance, interfere with the float level setting. The idle mixture screw is all but inaccessible, but adjusting it would only affect the idling setting, not so? I'm assuming that it is a fuel problem and it is out of it's warranty, being a 2006 model. Can anyone please assist with advice as I would like to tackle and attempt to solve the problem myself before taking it to a professional workshop.

Quote:

Originally Posted by Bokbal (Post 224095)

opening it to for instance, interfere with the float level setting. The idle mixture screw is all but inaccessible, but adjusting it would only affect the idling setting, not so?

Remember the old saying that carburettor is French for leave it alone. I'd be surprised if a virtually new Japanese bike was delivered with the wrong float level and the idle mix screw is unlikely to be connected with the symptoms you describe.
Restricted fuel flow into the carb would be my first guess. Has it just started misfiring recently or has it been doing it from new? Does it start /idle ok and run well in the mid range but just misfire as you use more throttle? How do the plugs look?

I had a similar-ish thing, though it would also be erratic at idle. turned out to be a split air hose. if you feel/listen around the airbox/hoses you may hear a hissing if there's air being sucked in.