So I just got a '90 CBR 600 a few weeks ago and ever since I got it, the bike would begin to sputter and cut out when under WOT past 5k, but will get to higher rpms if i just ease the throttle up to it. A few people told me that it probably wasnt getting enough air since it has an aftermarket exhaust and a stage 1 jet kit in it.

So what I did was take out the two foam filters that are in the airbox to see if that was the case. Took it for a ride and was able to give it full throttle and hit high rpms without any problem. I rode it for about 25 miles, and then it started to sputter again like it was outta gas and then died. There was a tiny bit of gas in the bottom of the tank, so I figured that it was flooded, waited about 20 minutes and it started back up with some trouble. Rode it for another 10 miles, then it did the same thing.

Then I put the foam things back into the airbox on the side of the road and tried to ride it but had the same problem where it was difficult to start, and almost killed my battery in the process. Eventually got it back on the road, but it kept acting like it wanted to cut out.

What do I need to do? I'm pretty sure I flooded the carbs, but was it from too much air going into the system? I'm kind of a newbie to sportbikes, so I am unsure of what to do.

 

Best way (IMO) to tell is get it up to where it's acting up...shut off engine and check a plug. They never lie.

 

If you don't want to mess with pulling a plug (I know they are a pain on the 600s) you could get it up to rpm that it starts acting up and slowly apply choke and see if it helps or hurts.

 

I was going to try the choke, but for some reason mine doesn't work? Even at idle if I pull the choke back, the engine does nothing. But I'm going to pull the plugs this weekend to see if it is fouled or not.

But do you think it would cause it to flood if there was too much air coming into the carbs right?

 

The term "flooding" refers to too much fuel, not too much air. If you had too much air coming into carbs, it would lean out and run rough. It could be any of a dozen (at least) things. First thing I would do is tear carbs down and see what you have and where everything is set. Then I would clean them. People go crazy with jet kits. Unless it's a high dollar/quality full exhaust, it shouldn't need much more fuel than stock setup. Too much is definitely not a good thing. When you remove needles, if it has notches where you can adjust it, you know it has a jet kit in it.
But before you do all that, take it out on road. It'd help if you had a long stretch in front of your house. With bike in at least 3rd, run it up to rpm's that it starts cutting out...then pull in clutch and hit stop button at same time. Then coast to a stop and pull a plug. Anything other than a light brown/beige color on the plugs will tell you some idiot has jetted the crap out of it and it needs to be retuned.