In this motorcycle tutorial you will learn how to calculate the manual valve shim size. Both exhausts have the same spec and both the intakes have the same spec so the video only shows one side being done.
The shims aren't made in 251, 252, 253, 254. It's either 250 or 255.
The two boxes represent the clearance and the shim. The two added together is the total area you have to work with. Subtract the desired clearance, this is the space left to be taken up by the shim. That's all there is to calculating the manual valve shim on a KLR650 as you will see in this video.
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