Busting Carb Needles, anyone ever seen this???

[Shum]

I have a 2003 RMK 700, has run great for the 2 years I have owned it. Last week I was out and I lost my left cylinder, diagnosed it to find when I stuck my fingers in the carb the needle was missing. Took it apart and sure enough right at the step down on the needle it had sheared off (1/2 of it still in the slide, the other 1/2 sitting in the jet and bowl). Don't see how this happened, so I got a new needle and replaced it. No binding, nothing feels wrong, strange...

This weekend 22 miles into a ride same problem, lost my left cylinder, fingers into the carb, and same exact thing. needle sheared straight off (very cleanly) right at the stepdown in the needle.

So now I am confused how this can happen. There is no bend, no bind marks, nothing in the jet. Has anyone ever experienced this? if so what did you find was causing it? First break I chalked up to happenstance, but 2 busted needles in less than 30 miles??? I must be missing something.

 

[Jay]

Thats bizzare, I can't imagine what would do that.

 

[WyoUltra]

Is there something in the cap that would cause the needle to not remain in place?? Is your cap coming unscrewed/somehow too tight? I really have no idea, I'm just trying to come up with ideas and suggestions for you. I wonder if it somehow got bent, and continually tried to work until it broke? Is it somehow misaligned? The first time it broke, did you clean your carbs right before that? (Could have somehow assembled it incorrectly?) I really find this baffling...

 

[kirk]

This may be a long shot, but check crank runout. It could be getting a bad harmonic/vibration in that side

 

[BB454]

If the "j" clamp is in place correctly it will hold the needle down so it doesn't come out of the needle jet. If that is there then vibration is your next possible problem. Does it have billet carb adapters or hard motor mounts? Either will cause excessive vibration and as mentioned above crank going out will make them vibrate too.

 

[Shum]

Is there something in the cap that would cause the needle to not remain in place?? Is your cap coming unscrewed/somehow too tight?

No, the needle slides nicely, no binding at all, and nothing coming apart...

I wonder if it somehow got bent, and continually tried to work until it broke?

The first one that broke had a ever so slight bend in it, but it had been in there for 2500+ miles. The second is perfectly straight and lasted 25ish miles (2 hours)

Is it somehow misaligned? The first time it broke, did you clean your carbs right before that? (Could have somehow assembled it incorrectly?) I really find this baffling...

No I have not had it apart, the first time It broke I simply replaced the needle. My plan now is to tear it apart and see what may be in there no though...

Thanks for the reply,

 

[Shum]

This may be a long shot, but check crank runout. It could be getting a bad harmonic/vibration in that side

Seems fine...

 

[Shum]

If the "j" clamp is in place correctly it will hold the needle down so it doesn't come out of the needle jet.

"j" Clip is in place was still holding the busted off top 1/2 (both times)

If that is there then vibration is your next possible problem. Does it have billet carb adapters or hard motor mounts? Either will cause excessive vibration and as mentioned above crank going out will make them vibrate too.

Nope stock rubber mounts, vibration seems as it has always been (normal). Nothing compared to my 900 The 25 mile bust was 100% trail riding (20-25 mph max) no full throttle.

still baffled, I'll let you all know if I find anything when I tear into it.

Thanks for the ideas...

 

[WyoUltra]

Did you find out what was wrong?

 

[Hardass]

Needles go through the slides are the slides moving forward and back in the giuides of the carb

 

[MARV1]

Is the small plastic washer under the e-clip to properly set it in place?

 

[sled_guy]

What color are the slides in those carbs? Carb slides worn which let them rattle back and forth? I haven't seen it on a 2002 or newer, but have seen it on older triples.

sled_guy

 

[turbodoc]

Busting needles

I have seen that a lot on rack carbs. Replace the slides they are worn out. Warm up idling rattles them back and forth and wears them out.

 

[Vincenthdfan]

Yep...I had a KX500 dirt bike that would break needles every time I would set the clip two from the top or above.

Once it did it when I was leading a desert race with a HUGE lead!

Another time when I was trail riding in the mountains, go figure.

I finally got so mad I called the Team Green racing hot line and talked to their race techs.

The mechanic told me "Oh yeah, we never run them above the middle like that...they'll break everytime from the vibes"!

Terrific...

Went to a different taper, ran the clip in the middle and never broke another one, ever.

 

[Shum]

So Last week I tore the carb apart looking for the issue. I think whomever said the slide is worn is mostly on. However In moving the slide front and back, back and forth I can not make the needle bind with enough force to cause a mechanical break (it barely rubs), but I am convinced somehow that the slides are too loose and that is causing my breakage. My thoughts are that the pilot for the jet is worn, but this is a press fit part and not a replacement part so lets just move on...

I have ordered a used carb for $125, at this point I have busted 3 needles at $26 each in less than 50 miles so buying a different carb I think will be the cheap route to fixing my problem. (in addition there are no needles this size left in Alaska)

Thanks all for the advice, if this new carb starts busting needles I 'll be back. with even more confusion.

 

[sled_guy]

It isn't a mechanical failure... rattling back and forth they fail.

sled_guy

 

[Shum]

It isn't a mechanical failure... rattling back and forth they fail.

sled_guy

I'd agree with you, but the failure rate is way too fast to blame vibration in my opinion. 3 needles busted in 40 miles. The mean life of the last 2 pins was about 45 minutes. Vibration would not just turn on like this would it?

If your correct my new carb should bust a needle as well?

 

[whoisthatguy]

Just buy another pair of carburetors and be done with it. People are giving them away, almost.

 

[sled_guy]

I'd agree with you, but the failure rate is way too fast to blame vibration in my opinion. 3 needles busted in 40 miles. The mean life of the last 2 pins was about 45 minutes. Vibration would not just turn on like this would it?

If your correct my new carb should bust a needle as well?

If they have hit a point where they rattle at a harmonic then it could happen quick... think about how many oscillations that needle can go through in 45 minutes at 8000RPM.

sled_guy

 

[hooky]

Wondering if the new carb fixed the issue? A buddy of mine has broken 2 in 50 miles or so. Slide was definately worn, replaced with a good used one after the first break, now broke another. I have worked at a Polaris/Skidoo dealership for 13 years and have never seen this.