Serious bog

I've got an '04 wee which I picked up in California. It's my second wee, my previous being an '05 I got whilst in Indiana. I never had an issue with my last bike. Recently i've noticed a serious drop off in power at 5,000-5,500 RPM which causes thebike to really stutter and struggle when the throttle is fully open. When I throttle back to 3/4 she surges ahead like a spurred quarter horse.

To try and remedy this, I've had the throttle bodies synced, replaced air filter, oil and filter, and run injector cleaner for a couple of tanks which relieved the symptoms albeit temporarily. I also had the fuel pump out and inspected the pre-filter for crud but it was pretty clean. I spoke with a friend who was a Honda mechanic for 30yrs and he said it sounds like it might be rinning lean. It seems strange that this has just developed though?

My bike has 90,000miles on the clock and has been ridden hard!

What could be causing this? Valve clearances? Fuel filter/pump? Is it some weird sensor issue that I'll need to pay a months rent to fix? Or is it something I can remedy with a couple of hours and a skinned knuckle or two?


Thanks in advance folks...

Nick