hey guys. to introduce myself, i am a rising senior at MIT and doing a summer-long internship at Caltech this summer. more importantly im a new (to me anyway) ninja owner.
a couple of months ago i took the BRC in va to see if i like riding. i fell in love with it immediately. and so after i got my class m designation i bought a '89 250 ninja with 12k miles in so-cal (where my internship is for the summer). I bought it from a private seller and upon the test drive found that it ran great, except for the last couple of minutes in which it idled at ~2.5k. but for the most part, it idled at ~1.3k and the throttle opened and snapped shut cleanly. from my inspection, the wiring was in great shape (as flawless as it can be for an 89) and all signals and brake lights were in working condition. The battery was brand new and the oil had just been changed. Before my test drive the owner told me that the last time the bike had been ridden was 6-weeks prior. because the bike had run well for about 10 minutes, i ignored the high idle in the last 2 minutes (mistake).
So i purchased the bike and left for a 30 min ride back to my apartment. after exiting the interstate 20 mi later and stopping at the first stop light, the bike stumbled and stalled. i had to pull to the sidewalk and after a minute or so, I got it started again. If i let the rpms dip below about 1.5k, it would start to stumble and eventually die. to prevent this, I set the idle at about 3k (where it seemed to be content to sit anyway) and made it to my apartment. Later that evening, I took the bike out again to re-evaluate the issue. after about 20 min of riding, the same problem arose. if i tried to set the idle at ~1.3k it would invariably stumble and stall. the only way to prevent this was by setting the idle really high (3k).
I am by no means a gear-head, but am very familiar with engine related issues. Because the bike had sat for 6-weeks, it was my initially impression that the carbs just needed a good cleaning. Because i just moved into my apartment, I didnt have the tools to do it myself. so i gave the seller a call and he agreed the carbs needed cleaning. i took the bike to him the next day and he cleaned and sync'ed the carbs. But after picking the bike up and warming up the engine, the same problem existed. I couldnt stick around with the seller and figure it out because i had to get to work.
I noticed that when i blipped the throttle there was some hanging, which would suggest that it was running a little lean. even though the vacuum lines looked like they were in good shape, i used some wd-40 to test for leaks. there werent any. I also tried adjusting the idle mixture to richen it up a bit. at about 3 turns out, I could get the engine to idle at about 2k but still had to be wary about it dropping below 1.5k, when it would stumble and die.
frustrated and out of ideas, i checked this forum for other ideas. some one else did post about idle issues and how replacing the pilot jets, even though it was clean, fixed it. i ordered two new pilot jets and two idle mixture screws (figured while i was there to replace them too), bought an excessive tool set and removed the carbs to replace them. The old pilot jets were perfectly clean and in good shape. the same for the idle mixture screws. even so i replaced them anyway. i did notice that the previous seller had done a very thorough job cleaning and syncing the carbs. but that did not fix the problem either.
now i am completely out of ideas. my throttle cable has a good amount of play, same with my clutch. the engine runs great about ~3k all the way to WOT. I have tried adjusting the idle mixture from 2 turns to 4 turns, and while richening the mixture brings the idle down, if i let the rpms dip below 1.5k, it stumbles and stalls when the engine is warm. i have scoured this forum looking for similar problems but havent been able to find a solution.
Does anyone have any ideas? I would so very much appreciate it. Thankss
my bike:
