I'm having the same issue as Donvier. I have an '01 zx9r with only 4000 miles, but mine is totally stock. The bike used to run great, but then it sat for a month or so (with the fuel turned ON) and that's when the issues started. Mainly no power below 3500 rpms. Sometimes it's worse and requires high rpms and letting the clutch out very slowly to start off without falling on its face. Then, at 3500 to 4000 it takes off like a rocket. I ran a double dose of Sea Foam through it and after a good bit of riding it seemed to work itself out. Shortly after this I noticed an increase in the occurrence of an issue I'd been having on start-up where the engine would lock up during cranking. I'd bump the starter button a couple of times before it would finally turn the engine over again and then would backfire on start-up and run very rich for a few minutes. It started doing this any time that it sat for a few hours. I was told by the dealer that there could be gunk on the needle and seat in the carbs that was letting gas leak into the cylinder causing hydro-lock.

I cleaned the carbs out and did find sufficient gunk in two of them, but now the bike runs worse! All the low end sputtering is back two-fold. I was told that I must've missed the idle jet or something, but I don't see how. In the bowl, I saw the float, the main jet, and then a smaller jet located right next to the main jet that stuck up almost as high. (the diagram in my haynes manual appeared to refer to this as the pilot jet) The manual mentioned some models having a recessed pilot jet covered by a plug. Is the E model one of them and if so where is it? Both jets were screwed down tight in every carburetor. That surprised me, but I took note of their positions and put them right back where they were (fully tightened). Also changed the plugs while I was in there. All had the normal rust color, no fouling, no white. The #4 plug was kind of wet when I pulled it out. That's the one that I suspect had the leaky carb, which was in fact the dirtiest bowl. Can someone please offer some insight before I tear everything down again without direction? Am I missing a mystery jet? So sorry for this novel, but details usually help. Thanks so much.

 

well, i'm aware of carb flooding if it sits for a certain amount of time with the fuel on.... i'm no expert at these things but have you tried the AF screws?

 

No I haven't. I didn't even see the screws when I cleaned the carbs. Am I correct in assuming that they're hidden beneath plugs? If so, do you know if the plugs can be removed without separating the carbs? I know I cleaned the main jet and pilot jet well, but I wonder if there could be more junk in there by the mixture screws that's causing the sputtering. Sound plausible?

 

Ok, I think I fixed the sputtering issue. I broke the carbs down and cleaned them thoroughly...again. I also removed the AF screws and cleaned them as well. The bike is running much better, but I need advice on the AF settings? Should all four carbs be set pretty much the same? Cylinders 1 and 3 were set all the way closed while 2 and 4 were backed out about 1 1/4 turns? It seems to me that they should be roughly the same. I thought maybe it had something to do with the different jet sizes, but that's on 1&4 and then 2&3. I had drilled out the plugs and on the two that were closed all the way, the drill bit barely knicked the top of the screws. Does it seem like the bit might've turned the screws in or do the settings seem normal? Help me out guys. I can't afford to just dump it off at the dealer so I'm stationary until I get it right.

 

I have never seen an A/F screw completely closed on a rideable bike.

 

I'm pretty sure that they got screwed in when the drill bit bumped them. I reset the screws to 1 1/4 turns and the bike runs great! BUT...on start-up the engine did the same lock-up and backfire routine as before. I don't get it. Sure seemed like hydro-lock from gas in the cylinder, but the gas was turned off while it sat for four days and the needle and seat had been thoroughly cleaned. No coolant is getting in the oil either.

 

Just recently purchased a -97 Zx-9r (zx900b-031789), with an aftermarket muffler. The engine sputters at rpm's below 3500 or better to say at throttle opening below 1/10th. Otherwise it works fine, and launches well from a standstill w/o any attempt to stall.

Have checked valve clearance and replaced air filter and plugs. If I rev the engine and let off the throttle grip, the rpm's fall below 1000 for a few seconds. Some say it is a sign of a rich mixture. On the other hand, when driving slowly w/ a warm engine and closing the throttle and opening the choke wide open, the engine runs much better and accelerates more speed on its own. This would indicate a lean mixture. I am confused.....do you guys have a cure to this problem?

 

Have you set your idle correctly? May have nothing to do with the rich/lean thing. Is there any slop in your throttle? Any other details available on possible mods that have been (improperly) done by previous owners? The 9's are bulletproof all-around bikes until rookies with flea market Chinese tools go hacking them up, and then wonder why they don't run properly. Once you get them set correctly, they run FOREVER.
More details? What did the old plugs look like? What kind of aftermarket pipe? Packing still inside the can? Is the engine allowed to warm-up properly before whacking the throttle? Have carbs been re-jetted (a-hem, improperly?) Any other aftermarket go-fast items on board?

"On the other hand, when driving slowly w/ a warm engine and closing the throttle and opening the choke wide open, the engine runs much better and accelerates more speed on its own."

So, are you accelerating with the choke on full, or are you idling/driving slowly? (i.e. since you're putting in more fuel with the choke on, yes; the bike will accelerate a bit on it's own.) What does it do when you THEN add throttle; does it bog like it's getting too much fuel, or does it accelerate?

Sorry to sound grumpy; not your fault (unless you're a hack with flea market Chinese tools.)
Welcome to the forums. We can get your bike sorted-out; this is not a tough problem.

 

stay with the basics. It is a '97, so inspect the other obvious stuff like loose boots, are they cracked with age? Know your ride ie... check your adjustment as mentioned, check your idle screws, fuel height and make sure that the emulsifier tubes are clear, etc. Slap on your synch gauges. Congrats on the new ride.

 

^Thanks, Drag.