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Discussion Starter · #1 ·
The one time I had a problem like yours was when I scratched a needle while reassembling a carb. Very fine scratch, you could hardly see it, but it profoundly affected the way the engine ran.

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Hey all,
I picked up an 85 Ninja 900 for free at the beginning of the summer. It needed some external work, but seemed to run OK.

After riding it a while, something just wasn't right. After a compression test, I found a couple cylinders had minimal to no compression. I popped off the head to find the valves pretty much shot. I got a good used head an put that on.

It now idles and accelerates fine, but while cruising (2500-3500 RPM) with no throttle, it runs rough, kinda like it's skipping. The second I apply the gas, it runs great.

I have been told to adjust the needles on the slides, but there is no adjustment (c-clip) on them. They just have a couple washers under them. I did try removing the washers (to lower the needle) and adding some (to raise the needle) but there was no change.

I also read something about an after-market single pipe (which the bike has) could cause this problem.
The carbs might even be after-market 'cause I remembers seeing a 1990 date on them while I was cleaning them.

Any help or a new road to take to troubleshoot this problem will be greatly appreciated!

Thanks,
M

[This message has been edited by M67 (edited September 27, 2000).]
 

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Have you cleaned the carbs at all since you
have had the bike? I'm not so sure it's a
needle problem since you said it's gives you
grief with the throttle closed. I would if
you haven't. I would also check for
vacuum leaks. Cracked hoses etc... You are
either leaning out or running too rich.
I'm guessing leaning out. Does the bike 'POP'
at all in the area of bad poor operation??

Good Luck,
Chris


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I really should be working...

[This message has been edited by chris_y2k_r1 (edited September 27, 2000).]
 
G

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<BLOCKQUOTE><font size="1" face="Arial, Helvetica, sans-serif">quote:</font><HR>I also read something about an after-market single pipe (which the bike has) could cause this problem.
The carbs might even be after-market 'cause I remembers seeing a 1990 date on them while I was cleaning them<HR></BLOCKQUOTE>


Is the pipe matched with jets ?
Even when you put on a slip-on on, you should rejet the carbs.


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Watch out where those Huskies go , Don't you eat that yellow snow ....


Adam
 

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Chris,
I have cleaned the carbs.
The problem isn't when the throttle is closed, it's when it's held at a constant speed - no acceleration or deceleration.
The only time I've heard it pop is when I'm decelerating from a high speed.
I will check for cracked/bad hoses.
Thanks for the help.

Squid,
I don't know about the jetting. The pipe was on there when I got it. How can I tell?
Thanks!

Leon,
I will check for a scratched needle - it's very possible, the needles have been in and out a bunch of times.
Thanks.


What about the carb-sync? I know it's off, would that cause a problem like this?

[This message has been edited by M67 (edited September 27, 2000).]
 

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I had a very similar problem a few years ago
on a Kawi. It was cracked intake hoses -
major vacuum leak.

If it is a bad needle you'll want to replace
it ASAP - otherwise it can permanently damage
the carbs.

I don't know that the carbs being out of
sync would cause the symptoms you are relaying.
Leon?? - I guess it's possible however they
would have to be way out of sync!?

If the carbs have a jet kit, you should have
a C-clip (Jesus Clip) on the needles and the
needles should have grooves in them where
you can move the clip up and down. If not
I would suggest getting a jet kit - they're
cheap - like $50.

It could be the pipe - possibly - if so a
jet kit should cure it but I would go for
the cheap stuff first - like leaks or needles
scratches. Let us know...


Good Luck!
Chris


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I really should be working...

[This message has been edited by chris_y2k_r1 (edited September 28, 2000).]
 

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Discussion Starter · #7 ·
Chris, I think that a synch problem would result in rough running & vibes throughout the rev range. I think that one of the answers we've come up with is the right one.
Problems in such a narrow range usually point to mixture. If the pipe was that bad, I think the previous owner would have made a greater effort to fix it, right after he installed the pipe, or he would have taken it off. Would you spend a bunch of money on a pipe and then leave it mounted when it made your bike run that badly? Not only leave it mounted, but ride the valves off the bike afterward? (600 Ninjas are known for soft intake valves). PS M67, I have seen some needles without circlips, just a "base" which determines the needles height. If this is the case, you can get the .020" shims and just slide them VERY CAREFULLY onto the needle from the pointy end up. I don't think that this will fix your problem, but it will probably make your bike run better once you do fix it. Good luck.

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Well, M67, looks like you had fun this summer, seeing the inside of a 900 Ninja and all. Your 2500-3000 rpm stumble sounds like a normal lean-out condition due to either dirty carbs or a Pipe. If you have a full pipe (sounds like it, stock was two mufflers), the lean-out is usually worse. Now the most noticible area when it is lean, is idling (people crank more idle speed into it to compensate), off idle, and steady cruise at up to 3500 rpm. Most guys put an aftermarket jet kit in it, thinking they're done. I'll save ya' the price of a useless "sticker". Take the carbs off, disassemble them, and remove the idle jet.It should say #35 on the side of it. Either procure some #37s, or drill them out with a #39 wire gauge drill bit. The #35 on the jet refers to .35mm, and you need to make them .37mm, understand. This jet controls idling, acceleration up to 3000 rpm, and steady cruise up to 3500 rpm. Put the #37 jets back in, and check to make sure the circuit to the idle bleed hole is clean. This hole is just in front of the throttle plate. There are 2 or 3 transition holes fed off this circuit in the floor of the carb right under and below the throttle plate. Make sure they're open. All these holes feed the gas to the engine until you're really moving, not the main jet! Now put the float bowls back on. You'll need to remove the caps on the idle mixture screws at the top of the carbs in front of the Diaphrapm cover. If you don't have a separate electronic tach to do an idle drop with, just open the mixture screws up between 1/4 and 1/2 turn (anticlockwise as you look down on them). Make sure the synch is spot on, and she should run like a champ. You won't need to bother the main jet, the increased airflow at high rpm will pick up the extra gas it needs without any tricks from you, at least until you put a flowed head and big cams in it. We also used to put a .020 shim (usually a 3mm washer) under the needle flange to give it a little progression, but it sounds like you may already have this. If you want to be thorough, get the specs on all the little pieces in your carbs from the dealer (it's on the microfiche), and check them while you do all the preceding. I've done this to 2000 bikes or so in the previous 20 years, and it works great. Heck, some Suzukis needed it done Brand New, just to get them off the lot. ;)

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function before form....
 

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Oh, yeah, I almost forgot. What Chris_Y2Kwhatever said about the cracked intake manifolds is a common problem on 10-12 year old Kaws, check for leks while it's idling by shooting a little WD-40 on the manifolds, and if the idle goes up, you found a leak. But be careful, don't burn the garage down.....<G>.

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function before form....
 

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Hey Guys,
thanks for the suggestions.
Since we've been getting big-ass surf here (on Cape Cod) the bike has been put on hold while the jet-ski has been getting all of my attention (check out http://www.rheinner.com/m/seadoo/5000.html )

I will probably get to the bike in the next couple days and let you know what I find.

Duke, there's a couple things you mentioned that I don't understand. So I will probably ask you about them when I get the carbs off and can't figure out what you meant.

By the way - you guys know of any easy way to get those @#$%^ carbs back on easily?

thanks for all your help!
M

[This message has been edited by M67 (edited October 01, 2000).]
 
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