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Yoshimura mechanics have experimented with plastic scoops and shrouds
around the cylinders. a type of ram-air cooling. Thew say the system lowers
oil sump temperature 50°F on hot days.
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The Yoshimura R&D of America technical team: (from left) mechanic Don
Sakakura. vice president Suehiro Watanabe. mechanic Dave Wolman.
A close look at the GS750 reveals worlts GS 1OOOR brakes. titanium
fasteners. hand-made aluminum triple clamps; exhaust system is stainless
steel with aluminum silencer,
Yoshimura has experimented with two intake tract variations. One version (above) involves porting and polishing the stock ports. which are
slightly curved. The other (below) involves milling the stock ports and carb
spigots off the cylinder head. welding up the holes. and machining new.
straight ports. The new ports extend into bolt-on manifold blocks and are
highly polished. In testing. Yoshimura mechanics have found that the
straight-port engine makes more peak horsepower with a powerband
from 8600 to 12000 rpm; the standard-port version makes less peak
power with a powerband from 8000 to 12000 rpm. As a result. Watanabe
says the straight-port engine configuration will be used if Yoshimura races
the bike at Daytona; elsewhere they prefer the standard-port configuration. Note external oil feed lines.
Yoshimura mechanics add idlers to the cam chain tensioning system. as
seen above. On the left side ofthe photo is the Yoshimura version. adding
idler sprockets between the cam sprockets and above the cam chain
tensioner; the tensioner itself is changed from being spring-loaded and
automatically-advancing to being mechanical. with a lock bolt. The rear
cam chain guide is shortened to work with the rear idler sprocket. The cam
sprockets are also lightened; the crank is polished. Below is a complete
Kokusan Denki COl ignition system.
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