Jet Needle Damage

[riffer]

Well, I found an excellent web page regarding this. See here (http://www.factorypro.com/tech/needle1.html).

Turns out that my problem is definitely slide hole abrasion. It's exactly the same sort of wear that is shown in the diagram.

Now the website says:

"If the needle rotates when it is installed, it will wear into a "funnel" shaped cross section. If it is prevented from rotating when installed, it will wear as shown in the diagram."

So I'm wondering... The needle itself has a c-clip, then a little nylon bush, then a thin washer and a larger nylon bush. So I can't see what there would be that would prevent it from rotating when its installed.

Anyway, sometime in the next 10 days my new needles should arrive and I'm going to try this out, but putting the old ones in there they rotate fine.

Go figure.

And another thought. Two of the diaphragms come away easily from the carb tops, two of them are stuck fast. Now I don't want to force anything in case I rip the diaphragms so I've left them alone, but I'm wondering. Do I need to put any sort of rubberlube on the diaphragms before I put the caps back on the carbs? Well actually they're on at the moment, I don't want to dry out the diaphragms as that could potentially cause a problem.

Anyone here know much about this?

[degrom]

Is the site you included off-line or is it just Telecom?

[riffer]

http://www.factorypro.com/images/logo_vector_and_rastor/suppban.gif

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Please click the above TEXT to navigate

Typical Needle Damage Areas
(and what causes it)
<center> http://www.factorypro.com/images/needlewear,TRX,64000k,AlanEccles.jpg
</center>
Alan Eccles sent in this scan of "Mink's" 64,000 km old, stock non-US model TRX 850 needle - Ouch! :-)
(That's about 35,000 miles for the miles parts of the world)
http://trx850.com/forum/index.php?sid=68abc9fccc975aa296d3594a78b669e8 (http://trx850.com/forum/index.php?sid=68abc9fccc975aa296d3594a78b669e8)

Got another winner? Throw in in a scanner, send a pic and we may put it on this page -
Send bike, mileage and your name -
<dl><dt> </dt>
<center> <table style="margin-left: auto; margin-right: auto; border-collapse: collapse;" border="1" bordercolor="#111111" cellpadding="5" cellspacing="0" width="85%"> <tbody><tr> <td rowspan="5" height="378" width="300">
http://www.factorypro.com/images/worn12.gif
</td> <td align="center" height="1" valign="middle" width="563">
<big>Descriptions and Causes</big>
</td> </tr> <tr> <td align="center" height="127" valign="top" width="563">Spinning E-clips (also known as C clips):
When installing E clips, make sure that they are a snug fit in the needle groove. If the clip rotates freely in the groove, it will "erode" the base groove and will eventually saw the needle into two pieces or the clip will actually fail. Replace distorted clips if available or, if absolutely necessary, gently pinch the clip to decrease its diameter. Replace the clip as soon as possible.</td> </tr> <tr> <td align="center" height="115" valign="top" width="563">Slide Hole Area:
If the needle rotates when it is installed, it will wear into a "funnel" shaped cross section. If it is prevented from rotating when installed, it will wear as shown in the diagram. Eventually, in either case, the needle will mechanically fail, but this wear, unless the needle physically breaks, usually doesn't cause a huge change in richness.
This needle is from a Legend Series fj1200 and is excessively worn, very fragile and should be replaced now.
If the diameter is only .002"-.005" worn at the slide, it won't appreciably affect jetting.
If the needle is worn and the needle jet is made of brass, you should inspect the needle jet for wear - especially if there is a problem with excess richness at low rpm. See Needle Jet Wear. (http://www.factorypro.com/products/Mikuni_needle_jet_buy.html)</td> </tr> <tr> <td align="center" height="115" valign="top" width="563">Emulsion tube rattling damage (base):
If the needle is prevented from rotating when installed, the needle will often show wear or at least a "witness mark" on one side of the needle. Usually, it's not the most significant wear area - with other areas of the needle or the needle jet being much more significant, as far as wear causing excess richness is concerned.
Steps in the needle, as manufactured, do increase wear in needle jets and also cause part throttle inconsistencies.</td> </tr> <tr> <td align="left" valign="top" width="563">
Emulsion tube damage (tip):
If the needle is too long, it may bottom out into the bore of the main jet or the end of the needle tube.
Common in Harley Davidson kits from some carb kit manufacturers.
Also, if a Keihin or Factory Pro K style jet is improperly used in a Mikuni carburetor, the needle tip may rattle on the 2.45mm lead-in diameter. The Mikuni jets have a 2.95mm lead-in diameter.
</td> </tr> </tbody></table> </center>
</dl>

[Lou Girardin]

Emulsion tube wear is common on RF's. If your km's are getting up, it'll pay to replace them too.

[pete376403]

I should pull the needles out of the GS1100 and see what they look like - its done a reasonabally high kilometerage (is that a word?) - 90,000+

While not denying that the needles do wear, I'd love to know what would make them rotate in the carb piston. I'd more expect to see wear at the point they are lifting out of the jet tube.

[riffer]

I'm thinking they should just spin of their own accord inside the diaphragms. I noticed when I had the diaphragms off that there was a bit of dirt - kind of like really fine sand in around the top of the carbs. Probably just a bit of fine road spooge, but if that got in the top of the slide it could stop them spinning.

Anyway, they're cleaned up now, everythings back together, and the bike's running fine. I had a good look at the needle jets, and there's no wear visible. There was also no wear visible at the bottom of the needles either, where you would expect to see wear if they were grinding away in the needle jet. Maybe mine just wore at the top instead.

Looking forward to riding to work tomorrow. :yes: