Anyone know anything about reed valve on a Vespa, looks a bit of a job to fit. Is it basically there to make a bigger bore carb work? Are the gains in performance, if any, worth the trouble and cost? Any thoughts?
A few reasons. LML did it to reduce fuel consumption and (presumably) avoid the extra maching process of the rotary pad. Plenty of people use one when the rotary pad is beyond repair. The larger ones can create a bigger intake than is possible with the rotary pad. They can also help with increasing crankcase volume and lowering crankcase pressure which can be beneficial. If you want to use a side draft carb, most of the manifolds available are for reed rather than for rotary. Also it allows the potential for greater flow downstream of the reed itself with flow around the crank rather than through the webs.
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