Inside Suzuki's X7

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.