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I finally got my carbs adjusted pretty close to correct and my new muff ears fell apart internally. I changed to a new style muffler that I liked better and surprise surprise my carbs are no longer jetted right. I ended up with my Amal MK2 carbs with the left carb needle in the bottom groove and still too lean. I talked to an "old guy" and he told me to shim under the needle to enrich it a little. I have not heard about shiming like that but it appears to work. I added a .025" washer under the c-clip to raise the needle a bit and the plug chop looked a little better. Anybody know the pluses or minuses of that?
 

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If it works, fine, but why not contact burlen (or a USA supplier) and ask what that might equate to?
Then fit a new needle of the appropriate size?

Assume this is the "standard" jetting and needles
 

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Once you go beyond the available notches on the slide needle, you need to go up or down on the jet. Shims are not the proper solution for jetting Amals; although this trick works on modern "nail" needles in CV carbs, TO A DEGREE.

Using shims to overcome improper jetting will not result in proper carburation across the throttle range.
 
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