Motocross history is filled with examples of creative ideas that were heralded as ground- breaking, but, because of the rapid rate of
change in development, many sank into the swamp of
forgotten technology. Although some are best left aban-
doned, others were truly innovative (if not ultimately
successful). MXA reveals motocross’ tech trivia. Do you
remember this idea? The Puch twin-carb MC250.
In the 1970s you could get two-strokes with two
different intake systems. (1) Piston port designs could
be used with or without reeds. It was called a piston port engine because the intake tract was aimed
directly into the back of the piston. ( 2) Rotary-valve
induction was unique in that the carb’s intake was
positioned on the side of the engine cases, where
the intake charge was timed to go into the bottom
end via a pie-shaped disc that spun on the end of the
crankshaft. Each design had its pluses and minuses.
Austrian moped manufacturer Puch entered the
250 World Championship with a totally unique take on
the piston-port/rotary-valve conundrum. The MX250
featured two 32mm Bing carbs—one feeding the back
of the cylinder and the other through a rotary valve.
Although the design was a racing success, with
Harry Everts winning the 1975 FIM 250 World
Championship on a twin-carb Puch MC250, it was
never a sales success. Puch only made 97 production
bikes in 1976. As a side note, Puch also made the
MC400 for Herbert Schmitz and Joel Robert to race,
but it had single piston-port carb.
IDEAS FROM THE ASH HEAP OF MOTOCROSS HISTORY