1980-1981 Honda Odyssey FL250 Shop Manual, Page 37Get this manual
8 ENGINE
Decarbonize with scraper, screwddver ,or wire brush taking care not to score sclratchFig.5 CyUnder HeadExhaust Port Decarbonizing
Standard
69.936,9.95 mm (2.15312.7:539 in 69.8mm (2.7480 iin