I have a 1998 ZX-900C1, and after I drive the bike for about 5 to 10 min, it randomly loses power for a split second, like a hiccup. Sometimes it does this going 60+ mph, but it happens much more often at the lower speeds especially off the line. It happens so bad off the line that it dies if I don't keep it revved to 6k while easing on and off the clutch (like a ladder). I have to do a ladder-type engagement of the clutch while at 6k to about 20 mph before I can fully release the clutch. I have also noticed that I hear a backfire occasionally at the low low speeds (during the ladder climb). I have not yet seen it hiccup while the clutch is disengaged (in neutral). The weird thing is that it doesn't do this at all in the first 5 to 10 min of driving. I would also like to mention that the engine itself purrs like a kitten in neutral, whether or not the engine is cold.

A little background...about a week or so ago, it would idle fine, but as soon as you put a load on it (drove it), it would run like dog with very little power. It ended up being that the carbs were "way off" on synchronization according to my mechanic. After he synched the carbs it seemed to run really well but now a couple weeks later it is acting up after the engine gets to running temp (water temp showing half way). It has acted this way through a few gas tanks worth of gas. Also, I replaced the fuel filter right before my mechanic synched the carbs.

My questions are as follows:

1. Is it possible that the carbs need to be synched again? I have read that you are supposed to synch them while the engine is at running temp, and I would like to hope that my mechanic would have done this, but I haven't confirmed with him and I wanted to ask the group your all's thoughts on this before asking him.
2. Is it possible this is due to running 87 octane fuel? My mechanic mentioned that the fuel he saw in the tank appeared to be a dingy yellow color and recommended I run that gas out and use a higher octane gas or a lower octane with a booster added to it.
3. What would cause the engine to behave differently when in gear and when not? Do engines use more fuel after a load is put on the engine?

Thanks in advance for your help!

Trent