Before you buy

Expensive parts.
Part name Price Pattern (Euro) Price Genuine (Euro)
Clocks (complete) 0 1100
Rear shock absorber 380 (Hagon) 650
Fork tubes + bushs 300 (ABE) 550
Carburettor parts 0 very expensive
Keyster carb repair kit 30 0
Front brake disc 200(EBC) 240
Complete rear wheel bearing carrier 0 180
Fuel Pump 0 150
Full set of pistons and seals, front caliper 130 140
Rear wheel bearings 0 110
Battery 50 110
Clutch friction plates, springs, lock nut and gasket 90 (EBC) 100
Air filter 25 60
Steering stem bearings 45 50
Starter motor 0 650
Cam chain 60 90
Spark plug wrench 0 15
Chain adjust C-spanner 0 15

Engine

Check cylinder compression.
Listen for unusual noises.
Check for oil leaks.
Check for engine oil contamination.
Check clutch.
Check that gears select and engage properly.
Check splines on gearbox output shaft.
Check spark plug threads in cylinder head.
Check for ugly corrosion etc.
Check for blue/black smoke from exhaust.

Clocks

Check that the clocks are working (duh) (If the speed clock is not working it might be the speedo cable).
Check that the pointers are not sticking in any position.
Look for fading on the clock faces.
After you drive the bike for a while check for fogging inside the clocks.

Shock absorber

I Don't really know how to check a monoshock but I suppose you could do the following:
Sit on the bike and hop up and down so that the monoshock compresses and rebounds.
If the damper is working properly I think it should compress, slowly rebound and then stop.
If it rebounds rapidly, that's not a good sign,
The monoshock should stop after it rebounds, but if it continues to bounce up and down that's not a good sign.
If the monoshock bottoms out very easily that's not a good sign.
If the bike feels bouncy or unstable while driving then the shock is probably gone bad.

Fork tubes

Check for "pitting", rust or nicks on the swept area of the fork tubes.
Sometimes when fork tubes are worn out you can notice that the chrome plating has
nearly worn through and it has a slightly different shade on the swept area of the tube.
Check that the fork slider does not jog with respect to the fork tube, if it does then the bushings may need to be replaced.
Pump the forks and check that they move cleanly and continuously and that the rebound is slightly damped.
If the robound isn't damped then there may be no oil in the fork.
If there is little or no oil in the fork it may just need an oil top up or new oil / dust seal or even new fork tubes.
If the fork bottoms out too easily it may need more oil or new springs.

Carburettors

Check that there isn't a strong smell of petrol from the exhaust fumes (Don't inhale exhaust fumes, very dangerous).
While driving the bike check that the engine responds consistently and properly to throtle changes.
Rev the engine to 7000 rpm and then release the throtle, check that the engine smoothly and quickly returns to idle speed.
Refer to the spark plug page on this website for futher info on spotting carb disorders.

Front Brake disc.

Check the disc for warpage (0.3mm run out sevice limit).
If the disc is badly warped then you may notice a pumping effect through the brake lever.
Check the disc for wear, 4mm minimum thickness.
Check that all the rivets are sound and tight.
Check for cracks between the holes on the steel part of the disc.

Rear wheel bearings / steering stem bearings.

Look at "Check your bearings".

Fuel pump.

The fuel pump is positioned near the rear wheel on the right side of the bike, it's cylindrical in shape.
With the engine running check that the pump "clicks" every few seconds.
Check for fuel leaks.

Front brake caliper

Check that the brakes fully release (some small bit of dray is inevitable).
Take the caliper off the disc and check for rust / corrosion on the pistons.
Squeze the front brake lever about 3 mm and check that all four pistons move slightly.
If one or more of the pistons are seized you may need to remove the pistons,
clean them and install new seals, if the pistons are damaged you will have to replace them, 30 Euro per piston.

Battery

Turn the engine kill switch off so that the engine doesn't start,
then turn on the starter motor for a few seconds to see if the battery dies.

Clutch

Drive at full throtle over humps and bumps to test the clutch.

Starter motor

Use your imagination.