Ok here is what we did on a 88 883, the owner had been racing a cb 750 up till that point.
We got a 1200 kit,but in those days there was no drop in. What we bought was,OEM 80 inch pistons (ie 1340 twin) STD size, a head template, head gaskets. That would be 3.50 bore.
When the EVO engines came out in 84 they went from a halfround head, to a bathtub shape, the template was to show the shape that a 1/2 round chamber looked like, you would remove material, to make it look like the older design. I did this gratis for my buddy, to help him out.
Next we bore 1/2 inch out of the barrels, yes 500 thou, and fit the new pistons.
I make up a fixture, to hold the stock mufflers, and cut the inner core out, leaving the outer baffles, not straight pipes, but very throaty.. alot like the OEM Screaming Eagle pipes. I think we left the crossover in place. We look at the aircleaner and we decide to pull out the element.. so stock carb, stock cover, stock pipes, with partial baffle removal.
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Now I recall starting to build pieces around this time to extend the swingarm 4 inches, but I am pretty sure , its not done by its first outing. we did not know what to expect of it. I think at this point, bone stock clutch, gearings, and maybe jetting)
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We get to the track, and he says it runs pretty good, by the end of the afternoon he runs a 12.7
We were were a bit surprised.. I think he spent around 600.00..