1977 Suzuki RM370B - 8-Page Vintage Motocross Motorcycle Test Article

Description

1977 Suzuki RM370B - 8-Page Vintage Motocross Motorcycle Test Article
Original, vintage magazine article.
Page Size: Approx: 8" x 11" (21 cm x 28 cm) each page
Condition: Good
They call it “big-bore” racing, but there
certainly isn't anything boring about
Open-class motocross. Give a group of
fiercely competitive, throttle-wrenching
hotshoes a half-liter of snarling, earth-
chewing horsepower each, add a few shots
of fast-running adrenaline and the breed
of racing you end up with is about as
subtle as a 50-car pileup. It’s a world where
finesse seems less important than sheer
daring, and the straightaway acceleration
is best likened to the muzzle velocity of a
cannon. From a purely practical stand-
point, it is power overkill al its knobby-
tired best. But it can be wildly spectacular
to watch and lots of fun to do.
When Suzuki's mighty RM370 first
showed up on the scene last year, it
brought with it all the forms of controlled
violence needed to be competitive in that
big-bore free-for-all. but it also added a
new dimension to the class: Affordability.
You could buy and maintain a 370 all
season long for about the same amount of
money required to get the other competi-
tive Open-class machines out of the
dealer’s showroom. The bike had its flaws,
some of which were obvious and others
that an average rider wouldn't notice in a
month . . . er,year of Sundays. All in all.
the 370 was a dynamite motorcycle that
quickly became the hot tip for the Open
class.
On another day in another lime,
Suzuki’s engineers might have kicked back
and taken it easy after completing the
impressive RM 125. 250 and 370 motocross
bikes. But they obviously knew that at this
point in history, the sport of motocross is a
particularly poor place for resting on one’s
laurels. Today’s successes quickly become
yesterday’s news. Motocross riders will
buy what works now, not what worked last
week or last night.
So for 1977 comes the RM370B. a sec-
ond-generation version of the top Open-
class econo-racer of 1976. With more
power, improved handling and other re-
finements, it’s clear that the few perfor-
mance shortcomings the bike had last year
were not overlooked, and that Suzuki
doesn’t intend to let the RM370 become
“yesterday’s news.”
THE BIKE: The RM370B remains
basically the same bike as before, but it has
incorporated numerous refinements de-
signed to correct problems or complaints
registered about the '76 model.
The engine was given a slight boost in
horsepower by lowering the bottom edge
of the intake port three millimeters and by
the use of a new spark advance curve built
into the CD1 system’s “little black box.”
The 36mm Mikuni carburetor now has a
300 main jet (vs. a 310 in the '76 model)
and an R-2 needle jet (vs. a Q-4 in the *76).
The small “by-pass” hole above the ex-
haust port (for easier kickstarting) is no
longer used. There is a new lightweight
piston, a higher compression ratio (7.6:1
vs. 6.9:1) and a longer locating pin for the
Keystone-type piston rings.
Otherwise, the 372cc engine is identical
to last year's power plant. The bore and
stroke are 77mm and 80mm respectively,
and the piston-port/case-reed intake sys-
tem remains unchanged. A two-petal reed
assembly sits in a vertical passage which
leads from the conventional piston-port
intake manifold directly into the crank-
case. With this design, the crankcase can
begin filling as soon as the piston starts
moving upward, even if the piston port is
not yet open. Too, the crankcase reed
supplements the piston port al those times
(like al high rpm) when the conventional
part of the system reaches its maximum
power output.
The rest of the porting is run-of-the-mill
from a design standpoint, with four large
transfer ports for delivering all that incom-
ing mixture up to the combustion cham-
ber, and one big exhaust port for getting
rid of it once it’s been burned. A through-
the-frame high pipe snakes the noise and
gases over, between and around the 370’s
vitals to terminate in a straight-through
silencer below the left rear edge of the seat.
The '77 muffler is almost one-and-a-half
inches longer than the '76 unit, but the
silencing efficiency is about the same. The
’77 bike registered 102.5 decibels during
our sound level testing, whereas the ’76
registered 103.6 decibels.
Straight-cut gears provide power trans-
mission to the huge wet clutch and drum-
And much more...
11080-7701-09