Hans,
Here's what little I know about these carbs' needles.
They are Keihin N427-48-xxx 66mm needles, with the last 3 digits being a three-letter code (taper 'A'/straight length 'L1'/straight diameter 'D'). These are available from http://www.motorcyclecarbs.com, but it's not quite that simple.
Here are half-assed specs for the three I have (number is stamped below the clip grooves):
271302: D .0988", long L1, mild taper (leanest) '76 CR250M 36mm
271006: D .0983", short L1, mild (dual?) taper (medium) '76 MR250 34mm
271309: D .0972", long L1, heavy taper (richest) '73 CR250M optional 36mm
The problem is that even if you're able to figure out exactly what needle you need (and believe me, it's not easy), not all of the letter code combinations are still available from Keihin, and if the straight diameter isn't fairly close to the OEM spec or otherwise doesn't match well with your needle jet, the bike may not even start. For example, the closest replacement needle for the 271309 needle above may be a N427-48-BGA; it's not available, and even if it was, the 2.465mm diameter doesn't even show up on the chart, although it does on the N427-46 57mm needle chart. N427-48-DCA and -ECA needles are available, but may end up as expensive toothpicks if the length and taper don't work for you. I believe some of the Honda needles were OEM-only as well, as the L1 and D specs are off the ends of the Keihin replacement charts.
Your best bet would be to try and find a needle on eBay. I got one recently along with the slide and spring (apparently it's pretty common to remove a carb for sale and leave the slide etc. on the cable).
All this is assuming your carb looks like the one in the picture.
Ray
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