Hi all. Last week I purchased my first bike, an 87 CBR600F for $400 not running. After fiddling with the wiring, if fired right up and I've been driving it for the past few days. Very happy with my $400 purchase

I've noticed some odd acceleration problems in the higher gears. The bike will pull very hard with great acceleration through first, second, and third gears. It will go up to 70+ mph in third gear and feel great. However, once I get to fourth, fifth, and sixth, it will barely accelerate and feels really bogged down. I can cruise in the higher gears and accelerate with about 1/4 throttle, but if i give it any more gas than 1/4 throttle the bike bogs down with no acceleration and won't rev up.

Thoughts? Other than the odd acceleration issue, everything else on the bike works great! Very fun!

Here are some pics, all work was done by previous owners, the only things I have done are oil change and messing with the fuel pump wiring. Sorry for low-res.

 

maybe it's running lean, though you'd think you'd see that in rpm range too, not sure how to check that beside a plug read and that doesn't tell you much, could be jetted wrong given the different exhaust but that too would seem like it would show up in other places too, not just 4/5/6.
or maybe tank vent issue, should try running with gas cap cracked open,

 

seafoam in the gas and running it seems to be clearing it up, I'm told