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Long story short:
bike was running great until about a week ago, now throttle response is jerky under 4,000 rpm. As of this morning, it seems like hard throttle application produces weaker-than-normal acceleration and a crappy exhaust sound (sounds more like a long, high speed fart than the normal growl). I wouldn't say I'm mechanically inclined, but I can do some basic stuff and I have the manual. Any thoughts, ideas, or suggestions on how to get the bike running smoothly again would be appreciated.
Long story long:
I think my old Ninja is starting to have some problems, and I figured I'd turn to you guys for some suggestions. I've had the bike for about a month now, and shame on me, but I'm just now starting to get around to making sure that it's mechanically sound. As it just so happens, the bike is just now starting to show signs that it might have some problems.
Two weeks ago, I started the bike, let it warm up, and took off. I immediately noticed that the engine sounded a little strange under 4000 rpm (the best I could describe it is it sounded more buzzy than its normal purr) and in that same rpm range the throttle felt relatively unresponsive. Anything above 4000 rpm, however, felt/sounded completely normal. After riding for about 2 or 3 minutes, the problem went away. At first, I thought I just needed to let the bike warm up for a longer period, so I tried letting the bike warm up well into the mid-range of the thermostat, but the strange sound/throttle response has just lasted longer and longer into my rides.
So this morning I start the bike up (leaning on its kickstand) and the revs were way below normal, even with the choke fully on (in fact, I had to give it some gas to keep it from dying). Normally, it revs to about 2500-3000rpm with the choke fully on, today it was at just under 1000rpm. As the bike warms up, the revs come up a little, but then the exhaust starts making little popping noises every now and then (it sounded like the pops an exhaust will sometimes make if you come off the throttle quickly while decelerating).
Well, I sit on the bike to get it back into the garage, and as soon as I straighten it up, the popping stops, the revs come up, and everything seems to be back to normal. I took it out for a quick ride, hoping all was well, but the jerky acceleration under 4000rpm was still there. To make matters worse, the bike didn't want to respond to hard acceleration. A hard throttle twist just produced weaker-than-normal acceleration and an exhaust noise that sounded more like a long fart than like its normal growl. Definitely not good.
My thoughts:
The owner cleaned the carbs about a week before I bought the bike, so for the moment, I am going to assume that the carbs are ok.
First, I think I need to just make sure I take care of some basic maintenance before anything else, and in particular, I need to change the oil/oil filter (the oil is very close to the bottom line on the glass gauge, and it's dark as hell). Maybe pick up a new air filter. I was thinking about replacing the spark plugs, too, just because who knows how long it's been.
Second, I've been filling the tank with premium gas (93 octane). After searching around today for some answers, I've read that this is apparently a bad idea. I'm going to switch back to using regular and run some seafoam through the tank.
Third, I've read a lot about these bikes having fuel pump/filter/relay issues, so I will probably pick up all three and keep them handy if my first two ideas don't produce any results. And in the event I try to install a new fuel pump/filter, I will definitely take the time to re-clean the carbs.
Finally, as odd as it might sound, I'm actually looking forward to doing a little wrench turning and getting to know my bike better. I just wish I had another bike that I could ride in the meantime.