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Needle Shimming confusion and suggestions

  • Thread starter Thread starter Do Little
  • Start date Start date
D

Do Little

Guest
Ok, so I got an 82 550 with the BS32SS Carbs on it and K&N pod filters. The guy I paid to rejet it did a bad job, so I've decided to try it myself. He at least got the synch right though.

So anyway, on good ole Basscliff's site (http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html#A05), it says to make the spacer at the top thinner, thus lowering the needle, to make it richer. Then, on the site BC links to that explains carb theroy (http://www.iwt.com.au/mikunicarb.htm), it says to make the spacer thicker because the higher up the needle is the more gas can get through. So which is it? The carb theroy site's explanation seems to make sense, but I figured it'd be a good idea to check.

Also, any suggestions on needle height for my situation? Right now it's running very lean at stock height and the throttle is very sketchy around 4,000 rpm and up. And just for the sake of information, size M3 washers fit perfectly.
 
A spring pushes the needle up against the washer on TOP of the clip. With a thinner washer the needle rides higher, which allows more fuel through the needle jet. The washers or shims below the clip really have no effect. So you pull out the thick washer above the clip and put in something thinner. One trick is to swap the thick one above the clip with the thin one below it.
 
When I shimmed the needles on my 550 I removed the thick plastic spacer above the circlip, measured it with the vernier caliper (0.099"), then worked out how many of the washers made up that same thickness (think it was four from memory), removed one washer and put it back together. So the final assembly just to clarify was from pointy end of needle: spring, original washer, circlip and three thin washers in place of the plastic spacer.

The distance between the clip positions on the needles with the five clip grooves is 0.040" (40 thou.) and the ideal adjustment is half of that which is 0.020" (20 thou.) so if my maths is correct 0.099" - 0.020" = 0.079" or 0.080" (80 thou.). So the thickness of the three thin washers placed above the ciclip should be about 0.080" or 1/2 a needle groove.

Hope this makes sense.

This proved ideal in my case and the motor pulls away from cold without any hesitation once the choke is turned off after about a minute after start-up.
 
Last edited:
I understand now. So basically your raising the needle either way. I guess I forgot how the needle is setup on these carbs, and the carb theroy page showed one with the clips so I thought I would be pushing up on it with the washers instead of creating more clearance room. Makes perfect sense now. Thanks guys.
 
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