[stoinkythepig]

My bike is apporaching 60,000 miles. I notice that when I roll on the gas at lower RPMs that it will pull harder at 1/2 to 3/4 throttle than it will at full throttle. It does not bog or anything at full throttle, just does not pull quite as hard.

I don't recall that it ever was like this in the past, so I'm wondering if perhaps my carb slide springs have softened up and are allowing the slides to open too much under WOT at low RPM.

It's a 2001 ZX9R, bone stock, except for a slight enrichening of the idle mixture done when it was nearly new to cure (successfully) an abrupt mid to high RPM off/on throttle response issue.

Any thoughts? I can live with this "problem" forever, if necessary, it's not a big deal since it's easily controlled by just gradually rolling on the gas. I'm just curious if it's just a matter of swapping in new OEM springs or not.

[SSearchVT]

The springs shouldn't wear out or change rate - it might be the carb slides not running as smoothly in the bores. If they're vacuum carbs - one or more of the diaprhams could have developed a pinhole leak.

My advice (free) - Live with it until you have time (winter) to and give them a good cleaning and inspection...

[TLRMan]

Actually putting in heavier springs will delay the slides, thus making them pull harder....
I'd look at your camchain for stretch first...