Varooming around the world on a Triumph 500; Jupiter's Travels, by Ted Simon. New York: Double-day. $14.

On a rainy October night in 1973, Ted Simon loaded up his factory-fresh Triumph 500 motorcycle and set off from Britain on a trip that was to take him around the world in four years and 78,305 miles.

Simon, an English journalist, chronicles that far- flung journey in "Jupiter's Travels," a story already told in part through on-the- road dispatches to the Sunday Times of London, which helped sponsor the trip.

It is for the most part an engaging account, a lightly entertaining, easy-flowing diary of Simon's travels across scorching deserts and rain-drenched mountains, through high-tech metropolises and remote villages locked in a bygone era.

Simon's talents of observation stand him in good stead. He writes vividly of Sudanese mountains "with smoothly rounded tops like mounds of ice-cream half licked," and of Argentine plains where "only the chocolate melancholy of the tango followed me across the Pampa."

At his best, he is also a sympathetic and intuitive portrayer of the vastly different individuals he meets, including a wonderfully comic trio of black Kenyans and a rowdy band of Australian truck drivers, or "truckies." The narrative is peppered with bits of humor, and it is also, as might be expected from a travel diary, laced with a steady stream of inner reflections which include some rather provocative probings of the roots of fear.

But to expect remarkable insights or enthralling escapades in these pages is to expect too much. For one thing, Mr. Simon's observations lack consistency. While he lavishes great detail and care on chosen places and people, he peremptorily dismisses others with a shallow tip of the hat. Of his three weeks in Johannesburg, for example, he grudges the reader only this much: "I saw the sights, lived the life, visited the black township, and learned something of the good and bad side of South Africa."

Perhaps even more disappointingly, given the course of recent global events, Simon offers virtually nothing on his journeys through Afghanistan and Iran -- countries through which he traveled at the end of his trip, as he barreled his way home from India.

Further, his personal reflections tend to be painfully self-conscious, awkward intrusions on the narrative. Simon's mental meanderings hit an abysmal low in India where he toyed with the absurd concept of considering himself to be a god - a self- important notion he eventually backs away from, but one which nonetheless is the basis for the title, "Jupiter's Travels."