Suzuki's 'ton-up 2-stroke', the
GT250X7, was hailed on its introduction in mid-1978 for its startling
acceleration
and mid-rpm pulling power. But would its performance figures hold up after,
say, a full year's riding? And how
does it rate for ease of servicing? Road Bike tested two X7s to find out.
TheX7 is not a revamp of theGT250 C,
its predecessor, but a completely new design from the wheels up. The
overall approach to the X7 has been aimed at lightness and acceleration for
the sports
market.
The new engine is very
compactabout 7.2 kg (16 Ibs) lighter than the previous model. It features
Suzuki's Power
Reed valve dual induction system which increases engine breathing for better
response through the rev range.
This new dual induction system
is the key to the X7's better pulling power over the GT250-C. The older
models
relied only on the conventional piston controlled fuel induction port,
whereas the X7 utilizes both the piston port and a
reed valve which is operated by crankcase pressure.
The X7's piston-controlled port
is designed to provide ihe fuel induction in the mid-rev range
(3.000-6,000rpm). and this is what gives this 2-stroke its mid-rev pulling
power. At the top-rev range (6,000-9.000rpm), the crankcase suction pressure
causes the reed valves to open, drawing in more fuel, giving extra power in
the lop rev band.
The gearbox ratios have also
been altered from the GT250 C to give the X7 a more even ratio between each
gear. The firsi gear ratio has been The X7 sports design of alloy wheels,
new exhausts and streamlined seat tank unit gives it style to match its
speed lowered so that the change between first and second gear is less
abrupt than was noticeable on the GT250-C.
The rest of the gear ratios have
been increased slightly making use of the X7's greater engine pulling power.
The kickstart
lever has been moved to the righthand side on the X7, compared to the left
on the GT250 C and can now be used while still in gear as long as the clutch
is disengaged.
The frame has been redesigned
and the twin downtubes found on previous models have now given way to a
large diameter single downtube. This increases frame rigidity and decreases
overall bike weight
On the road On seeing the bike for the first lime, its compactness and sporty lines are
most impressive. Once on the bike, the
lightness is immediately obvious and all the controls are easily accessible
and visible. Starting the bike at all times was easy
and the choke was necessary only when starting from cold. The choke is
either on or off and once the bike was running. the choke could be switched
off nearly immediately. The choke control lever which is awkwardly situated
on the lefthand carburcllor can be switched off
before pulling away.
Once under way. the bike had a
definite Jekyll and Hyde character. For between 3,000-6,000rpm the bike
would pull easily away in any gear without dropping down a gear—quite
encouraging for a lightweight 2-stroke. This was useful in heavy traffic. However. above 6,000rpm
and up to 9,000rpm the power up to 128 km/h (80mph) is breathtaking.
When accelerating hard in first
or second gear, it is very difficult to keepthe front wheel on the ground
and care must be taken not to over-rev.
Gear changing
The six-speed gearbox
is slick and smooth to use, but sixth gear is really useful only as an
overdrive gear above
112 km/h (70mph). Neutral was sometimes difficult to find. Accelerating was very smooth as the gear ratios were spaced
to
make maximum use of the mid-range pulling power. If extra acceleration was
required, it was instantly available by dropping down a gear to bring the
revs up into the 6.000-9.000 power-band.
The clutch coped with the power
and Ihere were no slipping problems. However, when the clutch was
disengaged, the clutch noise was very loud.
Road holding Overall, the road holding and handling were extremely good. When travelling
solo, the lightness of the bike made cornering superb. Only a slight shift
of weight on the handlebars was required to bank the bike into a corner
and it remained stable even on rough road corners was as due to the
suspension and dampers. At high
motorway speeds, the steering became very light; thus the bike
tended to follow any road faults. This wandering feeling was disconcerting,
especially when coupled with the wind buffeting felt when passing lorries on
motorways.
'Two-up' travelling
When
travelling two-up. the bike's characteristics were very different. On smooth
roads and motorways the bike was much slower and required constant gear
changing to maintain speed. The extra weight with a passenger stabilized
the bike at higher speeds, overcoming the light steering problem noticed
when driving solo.
Over bumps two-up, the bike developed a lurching feeling. As the forks hit a
bump, the front disc brake seemed
to snatch on, compounding the effect of the suspension. Even with the rear
damper settings altered the problem
persisted.
Braking
The braking is through a single front disc brake and rear drum brake. Both
brakes were very positive when used. If too much pressure was applied on the
rear brake at low speeds the back wheel could easily be locked. The front
disc was particularly sharp and had to be used with care. Once this was
realized, the effectiveness of the front brake was a definite benefit and we
hardly ever used the rear brake. Even in wet
weather the front brake worked well. For a bike of such performance,
only light pressure was required to brake effectively. One bad point
overlooked by Suzuki
is the lack of a front brake warning light. Since this brake is the most
commonly used and most effective, a warning
is a must for drivers behind you.
The front headlight was good for
night driving up to about 96 km/h (60mph) and the dip switch was easily
operated by the left thumb. No bulbs blew during the test but with the
vibration which occurred around 5.000 rpm, we half expected one to go.
The vibrations were noticeable
through the footrests and handlebars. The
vibration did not make riding uncomfortable and had no adverse effects on
long distant touring, save a slight tingle in the fingers after 100 miles.
The riding position was very comfortable
with the rider inclined slightly forward. This tends to put more weight on
to the wrists when riding and can cause some stiffness while getting used to
the position. The seat absorbs all bumps and vibrations, and all journeys
were accomplished without soreness.
Economy
Petrol consumption was hard on the pocket with an overall average of 12.8
km/1 (40 miles per gallon). The petrol consumption is better than the
GT250-C in all respects. When riding the bike sedately, over 16 km/1 (50mpg)
was possible.
The X7 250 definitely leads the
250 cc class in nearly all departments—acceleration, top speed, road
holding, braking and manoeuvrability. The X7's performance easily matches
larger class machines and represents good value for money if this is what
you are looking for. To ride the bike at its maximum performance requires
concentration and skill and this is not a bike for
In the workshop
Routine servicing of the Suzuki X7 is straightforward and, being a 2-stroke.
it is relatively simple compared with a 4-stroke. The toolkit is adequate for
simple service procedures. Specialized equipment you will need is an impact
screwdriver and strobe timing light.
The air filter is easily removed and the two bolts at the front of the
lefthand
side panel.
The spark plugs should be
cleaned every 1,000 miles as 2-strokes tend to oil up. The best method is to use your fingers
to insert
and tighten the plug, using the plug spanner for the final turn. As this
bike has capacitor discharge electronic ignition, it is unlikely that
the ignition timing will slip, but as an extra precaution, it is a aood idea
to check the ignition timing regularly. If system does break down, the whole
unit will have to be replaced, and this is an expensive business.
Timing
The timing must be checked regularly with a strobe light because if it slips
on this high-performance 2-stroke, the result could be a holed piston. An
impact screwdriver is needed to remove The CD ignition system requires no
maintenance and is more efficient than
the previous models' points systems the left-hand engine side cover; the six
cross-head screws have to be loosened, and the gearlever removed.
The engine should be revved to
6,000rpm and the middle notch on the alternator should coincide with the
crankcase While the cover is off, the oil pump adjustment can be checked.
This entails removing the plate behind the gearbox sprocket. You do this by
loosening the three cross-head screws which hold The throttle valve
dent mark is on the left-hand carburettor and can be seen by removing the
brass hexagonal nut. You position the dent at the 12 o'clock setting, by
turning the twistgrip, coincide with the aligning mark positioned to the
right of the cam.
Clutch adjustment
Clutch adjustment is necessary when play in the lever is over 4 mm. Cable
slack can he taken up by adjustment at the lever. If there is insufficient
adjustment at the lever, then adjustment must be made at the crankcase. This
is achieved by loosening the cable adjuster lock nut on the top of the
left-hand crankcase. Then the rubber cap at the
centre of the left-hand side cover has to be removed to gain access lo the
main adjuster. A ring spanner is necessary to loosen off the lock nut on
this adjusting screw. The adjusting screw is then tightened to take up any
slack and then
backed off a quarter turn. The two lock one on the crankcase cable
adjustment, should then be tightened. Chain adjustment and rear wheel
adjustment is simple with the use of the adjuster marks and bolts. You just
remove the cotter pin from the spindle
crown nut and then slacken the bolt off.
The chain is tensioned by
screwing in the adjuster bolts, until the centre play on the chain is 15-20
mm. Check that the adjuster marks arc the same on ment. On the test machine,
the chain needed adjustment after every 500 miles. At the same time as
adjusting the chain we also lubricated it by spraying
The transmission oil has to be
changed every 3,000 km (1,900 miles) and this was an easy procedure. The
drain plug is the 14mm bolt underneath the right-hand side of the gearbox.
Refill it with 800ml (1.4 pints) of a reputable make of SAE 20W.40.
Any corrections or more information on these motorcycles will be kindly appreciated.