Faults:

Valves frequently wear out and go out of adjustment. If they are poorly adjusted, the motorcycle is very difficult to start.

The nut on the right side of the crankshaft is made of aluminum and can loosen or break, causing a loud metallic noise (this is resolved by replacing it with the steel nut from later models).

The Keihin carburetor's "mid-body" gasket dries out over the years.

It tends to overheat in traffic or at traffic lights due to its compact radiator, so I don't recommend leaving it running for long periods without moving.

General Comments:

The EXC is one of KTM's top-of-the-line models, even though this particular one is getting on in years. I had the opportunity to take this bike to various places across Europe, and I rode it across practically all of Denmark.

As soon as I got on the KTM, it was clear I was on a competition machine. The high-quality Magura handlebar, set in a high and aggressive position, helps the rider properly distribute weight over the front wheel when entering corners. The long, narrow black seat makes it easy for the rider to lean forward or, if preferred—slide back to improve traction.

And traction is easily lost if you let the 510.4cc, four-stroke single-cylinder engine get out of hand. I couldn't imagine needing more power than what the KTM offers. It delivers tremendous low-end response (available right from idle) and feels very manageable and sure-footed when navigating challenging terrain. Power builds gradually into a strong mid-range before delivering an addictive surge at the top of the rev range. Even more impressive is the fact that the liquid-cooled engine runs quite smoothly for such a large-displacement single-cylinder.

A 39mm Keihin MX FCR carburetor feeds fuel to the formidable engine from a small 8.5-liter tank. Carburetion is excellent; the KTM never showed signs of faltering, and throttle response was smooth in any situation, crucial given the available power. The throttle has a fairly long pull, which aids control; a quick-action throttle would not be desirable on the 525. The bike starts easily from cold with the choke engaged and a quick press of the electric start button. However, the choke is somewhat tucked away, requiring some finger contortion to engage or disengage it.

Shifting gears is a breeze thanks to an incredibly smooth six-speed gearbox. Not only are clutchless upshifts extraordinarily fluid, but the clutch can also be dispensed with for downshifts in certain situations.

As for the brakes, they act on 260 mm front and 220 mm rear wavy, slotted discs. Both brakes perform well, though their stopping power is not exceptional. The levers are high-quality and feature adjustable reach.

A digital speedometer with optional trip functions makes navigation easier. Interestingly, the dashboard lights up whenever the vehicle moves, even when the engine is off. It is wired directly to the battery, as the vehicle lacks an ignition key, relying instead on a simple start/stop button.

In my opinion, the KTM is better suited to the experienced rider than to the casual off-road enthusiast. Furthermore, its handling is more physically demanding than that of some of its more docile competitors, which further reinforces my earlier point regarding rider experience.

Faults:

Nothing.

General Comments:

Awesome bike, super fast and reliable. The rider is the problem in my case.

I have de-restricted, re-jetted the motor because it does not come set-up to run right, it comes set-up to pass emissions test. It is the price you pay to have a race bike with a license plate.

I have added a radiator fan, and I run Evans NPRG+ waterless coolant. Never had any problems with overheating.

I have also done a fair amount of customization:

Taller softer seat.

Bigger tank.

Different sprockets.

Hand guards.

Engine guard.

Exhaust guards.

Brake rotor guards.

Fork tube protectors.

It goes on.