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Issue link: https://magazine.cyclenews.com/i/125858
50 eR, WR and MTkin ds of co m petition riding, I opted to
leave the transfer po rts stock and o nly
have .020 ins. m illed off the top of the
cylinder. Moclifying the exhaust port
s hape gives th e engine fantastic
mid -ran ge, and raising the port one
millim et er lets t he engine rev abo ut
1,00 0 rpm higher than the 6 ,0 00 at
stock.
T he n ex t st ep was to rework th e
in ta ke passage o n the cylinder , using a
high speed rotary grinder, turni ng the
two sm all intake p assages in to one big
on e th at al so feeds a ir/ fuel mi xture
directly into the finger port. This was
th e biggest part of th e project and to ok
an en ti re evening to do. Next, the piston
had to be reworked for t he reed
modification. D.H . suggests using four
hol es in the p ist on , one on top of th e
other on either side of the finger port
hole. This re ally looked fragile, and with
the piston b eing an inch thick where th e
tw o top hol es were and the cr an k pi n
inte rfe ring with flow , I decid ed to
modif y th e p iston similar to o u r past
Yam ah a project bik es, as shown , wh ich
p roved to be totally reliable. Cuttin g o ff
th e bo ttom p ortio n of th e piston skirt
allow s the same flow as four holes
would. without weakenin g the pi st on.
A f ter bolt i ng everyth ing back
to geth er, using th e 34 Mikuni which I
had an d changi ng th e 270 mai n j et fo r a
310, I went racin g. Well, like all
storybook en dings this o ne was happy
too . For the first three tu rns of every
moro, everyone else got to see what the
rear of my Husk y looks like . Second
gear starts are now a realit y , and even
then it to ok a 4.5 0 T rell eborg to try and
co me close to co n trolling the wheelspin.
Po wer is quick , bu t smoo th and
co nt ro lla b le from 2 ,000 to 7, 00 0 rpm .
We still go o n tr ail rides and 3 hour lon g
h ar e sc r a m b les whe n we ' re no t
m o t o cros sin g each we ekend. T he
mainten ance sc he d ule st ill includes only
two items, kee pi ng it wash ed an d the
chai n oiled. Reli ability wis e , after nine
month s it's st ill o n t he o riginal piston ,
reed petals and spark plug. 1 th in k I'm
in love.
•
36m m Bin g carb ureto r. T he 25 0 model
five and six speed Huskys (not
in cluding the 19 74 model 250 CR ) j us t
aren 't port ed radical ly enough to need
th at much carbure to r. Consequen tly ,
low spe ed power and throttle re sp o nse
are very p oor. S talling in tig ht first gear
t ur ns an d slow acceleratio n o ut o f th em
is th e resu lt . T he st ree t legal 25 0 MT is
e ven worse off with its 3 2m m Amal
T he so lu t ion to t he problem was
ver y simple : th e installation o f a 34 m m
Mikuni. The Mikuni h as all th ese n eat
little