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Old July 6th, 2011, 10:49 AM   #1
placetobe
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idle/stalling issue - ive read the million threads on this topic. i swear.

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:
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Old July 6th, 2011, 11:08 AM   #2
choneofakind
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how's the choke assembly look? it seems to me like it's acting as if the choke were applied from what you describe. does the choke work when you use it?
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Old July 6th, 2011, 11:12 AM   #3
choneofakind
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also you said you checked for leaks around the vacuum lines. did you check for leaks around the boots between the airbox, carbs, and engine?
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Old July 6th, 2011, 11:18 AM   #4
placetobe
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ah. forgot to mention the choke.

i have to apply fully choke to start it up. after about 5 sec with full choke, the engine runs up to about 5k and hangs there. i usually let it run at full choke for about 30 sec then to half choke for another 30 sec before cutting it off. the engine runs at about 5k when choke is full and 3.5k when choke is half. when i cut it off and before the bike is fully warmed up, it idles at about 1.5k. then after warming up, without choke, the idle either hops to 2-3k, hangs at about 1.5k or below 1.5k in which it tends to stumble and die.

i also examined the choke assembly when i removed the carbs and it seems to be in good shape. the choke lever on the bars has a good amount of play before engaging and seems to slide smoothly.
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Old July 6th, 2011, 11:24 AM   #5
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your pilot circuit passages in the carb sounds like they are clogged. were they cleaned out when the carbs were cleaned previously? sometimes it's not only the jets that get clogged, but also the passages the fuel flows through.
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Old July 6th, 2011, 11:33 AM   #6
placetobe
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to check for vacuum leaks i checked all the boots mentioned as well as around the fuel petcock.

i did notice a very slight leak around the left airbox boot, not because of cracking but because a slightly loose fit to the carb intake. however, it is my understanding that that leak should not greatly affect the performance of the carb because the carb intake is not under significant negative pressure and is a leak before the mixture of fuel and air... i could of course be mistaken.

could this be the source of the problem?
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Old July 6th, 2011, 11:35 AM   #7
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are you saying a clamp is loose?

any intake leak is a bad thing and yes, that could be the source of the problem.

also, when was the last time the valves were adjusted/checked?
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Old July 6th, 2011, 12:10 PM   #8
placetobe
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Quote:
Originally Posted by kkim View Post
are you saying a clamp is loose?

any intake leak is a bad thing and yes, that could be the source of the problem.

also, when was the last time the valves were adjusted/checked?
i sent the guy who cleaned the carbs out the first time an email to check on the circuit passages.

as for the intake, i dont mean the clamp is loose. it just isnt as tight as any of the clamps on the carb to engine boots. when i checked for vacuum leaks before i and noticed the slight leak around the airbox boot, i tested the issue by completely removing both boots (i ran it for a very short amount of time because it was running on unfiltered air) and the same problem existed.

and as for the valves, i dont know when they were last adjusted. do you think checking them will help?
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Old July 6th, 2011, 12:18 PM   #9
placetobe
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oh. and thanks kkim and choneofakind for your help. i really appreciate it.
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Old July 6th, 2011, 12:18 PM   #10
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checking/adjusting valves couldn't hurt. you should be coming up on your third check at 12k. if they've never been done, I would say it would be a good idea to check them, regardless if they are the cause of your problem or not.

http://faq.ninja250.org/wiki/Do_I_re..._6000_miles%3F

if you're saying the air leak isn't the cause of your problem, I go back to clogged pilot circuit passages as a possible source.
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Old July 6th, 2011, 02:47 PM   #11
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Valve check time, previous owner would never cough up that kind of dough. Also I'd replace all those rubber hoses and filters. How's the rubber on the tires, in fact what tires are on the bike (make, size and especially year).
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Old July 13th, 2011, 01:26 PM   #12
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Quote:
Originally Posted by coondog View Post
Valve check time, previous owner would never cough up that kind of dough. Also I'd replace all those rubber hoses and filters. How's the rubber on the tires, in fact what tires are on the bike (make, size and especially year).
Well. I did a valve check this morning. The valve clearances were way off for the exhaust, not so bad for the intake. I adjusted them to about 0.105 mm for intake and 0.140 mm for exhaust and resync'ed the carbs. Hopped on and rode for 20 or so min, and noticed the idle had jumped to about 3k (from 2.5k). When I tried to reset it to 1.5 k, it stumbled for about 15 sec and stalled. The engine definitely runs smoother since the valve check but that pesky idle problem still exists.

Both tires are relatively new, 90% tread still exists.

Also found out when the seller cleaned the carbs he did clean out the pilot passages thoroughly...

coondog, when you say replace rubber hoses and filters, you mean fuel hoses, vacuum boot etc? Thanks!
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Old July 14th, 2011, 06:40 AM   #13
GeorgeRYoung
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You've tried a bunch of things but I saw no mention of these:

1) Battery voltage, does it drop to less than 12V at the 1500 RPM idle?

2) If you suck on the vacuum tube going to the petcock, do you get a mouth full of gas?

BTW I also have an '89, nice pic you posted.
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Old July 25th, 2011, 05:44 PM   #14
polecat
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got any updates on this? The wife has an 89 250 that is doing the same thing. The carbs have been completely ruled out on hers though as I have had them checked by 3 different mechanics, after giving up on them myself. The last one who used to race a 250 told me he thought it was a vacuum issue with the petcock and I replaced it with a used one but still happens. The tank has been coated so that could be an issue but I am at a loss on this one.
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Old August 11th, 2011, 10:00 AM   #15
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Quote:
Originally Posted by choneofakind View Post
also you said you checked for leaks around the vacuum lines. did you check for leaks around the boots between the airbox, carbs, and engine?
Correct me if I am wrong, but there is no vacuum on the boots from the airbox to the carb. The only downfall at a leak here is drawing in unclean air that didnt pass through a filter.

Double check and hose it down with some carb/choke cleaner or WD40 around where the boots are from the carbs to the block.
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Old August 12th, 2011, 07:38 PM   #16
placetobe
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Today I actually completely fixed the problem. It was actually my fuel petcock that was the issue. Apparently when the bike was idling, the petcock would not allow fuel to flow through. The float bowls were thus full enough to allow fuel to flow through the needles but not full enough to allow fuel to flow through the pilot jet, which are higher in the float bowls. It now idles right at 1300 rpm with no hanging. its been a great day.

Quote:
Originally Posted by polecat View Post
got any updates on this? The wife has an 89 250 that is doing the same thing. The carbs have been completely ruled out on hers though as I have had them checked by 3 different mechanics, after giving up on them myself. The last one who used to race a 250 told me he thought it was a vacuum issue with the petcock and I replaced it with a used one but still happens. The tank has been coated so that could be an issue but I am at a loss on this one.
polecat, sorry to hear you are having similar issues. Before realizing it was the petcock, i was advised to check the spark plugs for oil deposits. the oil could be causing misfiring which could then cause stalling. fix would be to replace the piston seals... i think.

along the same wavelength as my problem, another possibility could be your floats. if they somehow are floating falsely high, they could shut off fuel to the float bowls before they are full. otherwise im as stumped as you.
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Old August 12th, 2011, 07:57 PM   #17
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Originally Posted by d16soda View Post
Correct me if I am wrong, but there is no vacuum on the boots from the airbox to the carb. The only downfall at a leak here is drawing in unclean air that didnt pass through a filter.
right. I was just thinking might as well check for an air leak at the same time. extra air would lean the mix and cause issues
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Old August 12th, 2011, 11:42 PM   #18
CynicalC
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Originally Posted by d16soda View Post
Correct me if I am wrong, but there is no vacuum on the boots from the airbox to the carb. The only downfall at a leak here is drawing in unclean air that didnt pass through a filter.

Double check and hose it down with some carb/choke cleaner or WD40 around where the boots are from the carbs to the block.
Yes there is a slight vacuum. The airbox is not completely free flowing, it's restrictive and the bike won't run quite right if it's not sealed properly. That's why you need to rejet when switching to pod filters.
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Old August 14th, 2011, 10:36 AM   #19
polecat
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Quote:
Originally Posted by placetobe View Post
Today I actually completely fixed the problem. It was actually my fuel petcock that was the issue. Apparently when the bike was idling, the petcock would not allow fuel to flow through. The float bowls were thus full enough to allow fuel to flow through the needles but not full enough to allow fuel to flow through the pilot jet, which are higher in the float bowls. It now idles right at 1300 rpm with no hanging. its been a great day.



polecat, sorry to hear you are having similar issues. Before realizing it was the petcock, i was advised to check the spark plugs for oil deposits. the oil could be causing misfiring which could then cause stalling. fix would be to replace the piston seals... i think.

along the same wavelength as my problem, another possibility could be your floats. if they somehow are floating falsely high, they could shut off fuel to the float bowls before they are full. otherwise im as stumped as you.
good to hear you got yours fixed and I think I may be having the exact same problem I threw another petcock on there that I had laying around and the bike runs 10 times worse and this petcock is leaking fuel much worse than the other one. So I just reordered a rebuild kit for it. Hopefully this takes care of the problem.
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