First, a confusion worth clearing up: this Kawaguchi is not the lake town at the foot of Mount Fuji, which is spelled Kawaguchiko and lies far to the west. This is Kawaguchi city in Saitama, a big, busy place of nearly half a million people just across the Arakawa river from northern Tokyo. On a ride to Shosenkyo and the Fuji lakes, it is where you leave the capital behind, or where you come back into it, and it is a sensible place to eat before or after.
Kawaguchi has an honest working past. For much of the twentieth century it was Japan's great cast-iron town, full of small foundries with tall cupola furnaces, and it was famous enough for a 1962 film, Foundry Town, starring the young Sayuri Yoshinaga, which showed the life of working families among the chimneys. Most of the foundries have gone, replaced by apartment towers, but the city still has a certain no-nonsense character. In the Angyo district, to the east, nurseries have grown garden trees and bonsai for centuries, supplying the gardens of Tokyo, and the area is still full of greenhouses and plant markets.
As a food stop, it offers everything Japanese towns do well: ramen shops with counters and ticket machines, family restaurants, gyudon chains, curry shops, and convenience stores where you can grab onigiri, cold tea and coffee in a can. Look for places near the stations, especially Kawaguchi station, where there is a lot of choice. Parking for motorcycles can be tricky in central areas, so look for designated bike parking rather than leaving it on the pavement.
The riding here is urban and slow. Traffic in Saitama is heavy, with lots of lights, trucks and delivery scooters, and the main roads, like Route 122, are wide but crowded. The Shuto expressway and the Tokyo Gaikan ring road cross the area and are quicker, though they charge tolls and have rules for two-up riding. Once you head west towards the mountains, things change completely, and the roads into Yamanashi climb through forests and valleys toward the granite cliffs of Shosenkyo and the lakes under Fuji.
Fuel is easy to find, and many stations in Japan are staffed and will fill the tank for you. A good meal and a full tank here, and you are set for the long day west.