The late great Roland Pike knew a thing or two about single cylinder OHV bike heads. Amongst other things he was responsible for much of the development of the BSA Gold Star in the 1950's. Here is an interesting snippet from his memoirs regarding inlet port work that you may find interesting. i have been following your progress having once owned a very fast MOV that had been used for sand racing. Just toadd, I miss my regular dose of French Fowl Longhi exploits
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ttp://www.beezanet.com/beezagent/rolandpike/roland%20pike%20memoirs.pdf
Excerpt from page 18
One of the strangest occurrances to do with carburettors was when one day Reg Wilkes sent an apprentice from the test shop into our,
main shop for a 1 3/32 GP carburettor and he misread the size and gave Reg: a 1 3/16th carburettor and they immediately got quite a
jump in power. They reported this to me and I went to the shop and the test was repeated and there was no doubt it was quite a gain in
power. I suggested to Reg to open the port to match, immediately we lost what we had gained plus a bit more, so we made a thin
sleeve and pressed it in and the power was back. We repeated this on other engines always with the same results. A number of private
owners of DBD Gold Star noticed the carb being bigger than the port and opened up the port thinking to gain power, but not having a
dyno were not aware of the results. Later on we fitted a venturi behind the carb and picked up even more power. The smallest diameter
of the venturi could be 80% of area of the carburettor. We tested this on several engines and it always worked and seemed to improve
carburation.