TO BE stranded at 4,350 metres above sea level on a thawing glacier with a 350kg motorcycle slipping uncontrollably underfoot can be unnerving. Stomping the pedal repeatedly in the forlorn hope of kick-starting the bike proved futile until, in what looked like a measured move, the hapless rider pulled a knob near the engine. After the next shot at the pedal, the bike puttered. A couple of kicks later it jolted back to life. Back in his saddle, the motorcyclist shifted into first and, bouncing over the rocks beneath the icy waters, he made it to the other side. A crowd watching his ordeal from the banks cheered. He had just crossed the "Pagalnala", or the "Mad Stream", a challenging motoring path in Ladakh, a vast, cold, moutainous desert situated in Jammu and Kashmir.

What ensured that he would not be late for supper that evening was largely physics (though, admittedly, composure played a part). On pulling the knob, the choke valve in the carburetor which regulates the air-fuel mixture that keeps the engine going swung into action. The job of the choke is to reduce the airflow to the combustion chamber and increase fuel intake. The resulting richer fuel mixture burns more easily and helps to resuscitate a cold engine (the technique was often used in the old days when cars still had a manual choke on nippy winter mornings).

On this occasion, though, the rider enjoyed some good fortune, too. Miraculously, the running water had not clogged the exhaust pipe, or worse, snuck into the air filter located near the seat. Had the fluid found its way to the carburetor through the air pipe and subsequently into the combustion chamber, the engine would have seized. Though rare, such problems can be overcome with basic knowledge of bike maintenance. A bigger concern in Ladakh was the altitude.

Take Khardung La, a mountain pass which, at 5,359 metres, is the world's highest road for motor vehicles. Here, it is common to find tourists trundling along and breathing heavily. "Just like us humans, motorbikes too suffer from altitude sickness," quips Yogesh Sarkar, who runs BCMtouring.com, a popular travel blog. The relative amount of oxygen in the air remains fairly unchanged at around 21%. But the air gets thinner and thus a greater volume is required to burn fuel in the combustion chamber. To tackle this, most bikes are equipped with an electronic fuel-injection system which pumps fuel under high pressure through a small nozzle. An oxygen sensor positioned in the exhaust pipe automatically regulates the air-fuel mixture based on the ambient temperature. Thus equipped, bikes are ideal for freeway riding, but are not cut out to ford wild streams or plough through squelching bogs.

Bikes which sustain the rigours of mountain riding rely on the older technology of carburetors to do the same thing. Carburetors lack the precision of electronic fuel injection and burn more fuel as a result. But they are cheap and can be repaired or replaced easily. It comes as no surprise, then, that Royal Enfield, the world's oldest surviving motorcycle company, has wisely continued to cater to aficionados of such rides. Each year, hundreds of them (like the one in the picture) explore the unpaved and remote glens of Ladakh on just such a vehicle. And the biker-friendly trail ensures that, eventually, help will always turn up and no biker will be left in the lurch.