Maintenance & Technical > KX500 Original

Keep Breaking Carb Needles

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2-Stroke Tom:

--- Quote from: Twosmokerfan on November 06, 2012, 12:08:25 AM ---I had a spare 38mm carb and too the security bolts out from part of the carb that the main jet screws into (not quite sure of the name) from the bottom, and the needle goes into the top and swapped them over.  It has one of those special torx bits with the stub in the middle of it.  Have a look when you pull your carb off.  You can't miss it.
--- End quote ---

Thanks Twosmokerfan, you were right about this part which I have found out is call the jet block that I can supposedly order from Sudco. Can't find the replaceable needle jet that screws into it anywhere though. I think I may have found a lead to my problem. I just put a new slide, jet needle, clip, and retainer in. I pulled the float bowl and main off to see what the needle looks like from the bottom and in the picture here you can see that the needle isn't centered:



This could be causing it to break, but how odd is it that the bike runs perfect for a year of riding, then breaks a needle. No symptoms of any needle hanging up at all. Now what?? I may just buy a new carb if I have to keep throwing parts at this, some of which may not even be available. Already had to buy float, slide, gaskets, etc, and that was about $100. Plus, this is the third carb needle I've broke at $25/ea. I can get a new carb for around $210 delivered, so this may be the smartest route. I can just swap out the jets.

Also, as usual with these bikes, something was always different and/or modified. Team Green used a notched slide while the replacement oem slide I received is not notched. It's hard to see, but look at the top of the picture for comparison (bottom of the slide):

Twosmokerfan:
Hi 2S Tom,

Yes, that part comes out and then entire internals of the carb comes out up to the venturi part that is in the throat of the carb.

I might suggest that the movement of the needle over the past year has caused fatigue in the clip area, causing it to snap.

I changed mine out from my spare carb (because I didn't know how many miles the original had, and knew exactly how many hours the replacement had done) after I couldn't get it to jet correctly.  After that, no more jetting issues and (so far touch wood) no broken needles.

It is just a theory worked on seeing I had replaced the needles, slide, and mostly every other component in the carb, and still not able to get it to jet.  Just my theory.....

Hope it works out.

2-Stroke Tom:
Well, before my trip last weekend, I went to jet my brand new Sudco replacement carb, and I finally got to the bottom of my issue with breaking carburetor jet needles. Believe it or not, it had to do with the jet needle retaining clip where the throttle cable attaches inside the carburetor. A couple dollar part!! As you can see in the picture below, the new Sudco retainer is relieved underneath so that it does not "trap" the jet needle clip. I had both slide and needle assemblies in my hand (both brand new, one was oem and one was Sudco) and it was apparent that the oem retainer caused the clip on the needle to be trapped, and would not allow the needle to rotate and basically self center.


So, everything is brand new from Sudco with the exception of the new OEM jet needle I installed.


And, everything installed with new compression release modification.


The end result was the bike ran great. The bike ran great with the higher compression head gasket and the 50/50 mix of 100 octane VP race fuel/91 pump gas. Thanks to Motorrad's advice, I was confident I wouldn't have any problems. The only think I'm going to do is go to a N82M needle per Team Green Specs (instead of N82P), now that the compression is increased an race gas is being run. I could definitely feel the power difference, so I'm sure some throttle chops to get the jetting spot on would even help more, but the bike pulled hard with no hesitation, and fired first kick all day, so I never messed with it.

Motorrad:
shouldnt need 50/50    you could get away with just tossin 1.5 gal in a 5gal can.   just to "FIX" the s**tty california fuel problem.

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