Yes the KDX had a bigger cap thread. Interestingly though the KDX has the same thread as the PE 400 and the XR 500
Shouldn't be too hard to find the KX cap
My notes have 2 part No's listed
I think the first group might be the original while the second group / part No will be the superceded to part??
One will most likely be a slightly different shape.
Part # = 51049-1001
Part Description = FUEL TANK CAP,51049-1006
Model Count = 17
KDX80-B2 82 80 KDX80 OFF ROAD
KX80-C1 81 80 KX80 MOTOCROSS
KX80-C2 82 80 KX80 MOTOCROSS
KX125-A4 78 125 KX125 MOTOCROSS
KX125-A5 79 125 KX125 MOTOCROSS
KX125-A6 80 125 KX125 MOTOCROSS
KX125-A7 81 125 KX125 MOTOCROSS
KX125-B1 82 125 KX125 MOTOCROSS
KX125-B2 83 125 KX125 MOTOCROSS
KLX250-A1 79 250 KLX250 OFF ROAD
KLX250-A2 80 250 KLX250 OFF ROAD
KX250-A5 79 250 KX250 MOTOCROSS
KX250-A6 80 250 KX250 MOTOCROSS
KX250-A7 81 250 KX250 MOTOCROSS
KX250-B1 82 250 KX250 MOTOCROSS
KX420-A1 80 420 KX420 MOTOCROSS
KX420-A2 81 420 KX420 MOTOCROSS
Part # = 51049-1006
Part Description = FUEL TANK CAP
Model Count = 62
KX60-A1 83 60 KX60 MOTOCROSS
KX60-A2 84 60 KX60 MOTOCROSS
KX60-B1 85 60 KX60 MOTOCROSS
KX60-B10 94 60 KX60 MOTOCROSS
KX60-B11 95 60 KX60 MOTOCROSS
KX60-B12 96 60 KX60 MOTOCROSS
KX60-B13 97 60 KX60 MOTOCROSS
KX60-B14 98 60 KX60 MOTOCROSS
KX60-B15 99 60 KX60 MOTOCROSS
KX60-B16 2000 60 KX60 MOTOCROSS
KX60-B2 86 60 KX60 MOTOCROSS
KX60-B3 87 60 KX60 MOTOCROSS
KX60-B4 88 60 KX60 MOTOCROSS
KX60-B6 90 60 KX60 MOTOCROSS
KX60-B7 91 60 KX60 MOTOCROSS
KX60-B8 92 60 KX60 MOTOCROSS
KX60-B9 93 60 KX60 MOTOCROSS
KDX80-B2 82 80 KDX80 OFF ROAD
KDX80-B3 83 80 KDX80 OFF ROAD
KDX80-C1 84 80 KDX80 OFF ROAD
KDX80-C2 85 80 KDX80 OFF ROAD
KDX80-C3 86 80 KDX80 OFF ROAD
KDX80-C4 87 80 KDX80 OFF ROAD
KDX80-C5 88 80 KDX80 OFF ROAD
KX80-C1 81 80 KX80 MOTOCROSS
KX80-C2 82 80 KX80 MOTOCROSS
KX80-E1 83 80 KX80 MOTOCROSS
KX80-E2 84 80 KX80 MOTOCROSS
KX80-E3 85 80 KX80 MOTOCROSS
KX80-G1 86 80 KX80 MOTOCROSS
KX80-G2 87 80 KX80 MOTOCROSS
KX80-J2 87 80 KX80W MOTOCROSS
KLF110-A1 87 110 MOJAVE 110 SPORT 4-WHEEL ATV
KLF110-B1 87 110 MOJAVE 110E SPORT 4-WHEEL ATV
KX125-A4 78 125 KX125 MOTOCROSS
KX125-A5 79 125 KX125 MOTOCROSS
KX125-A6 80 125 KX125 MOTOCROSS
KX125-A7 81 125 KX125 MOTOCROSS
KX125-B1 82 125 KX125 MOTOCROSS
KX125-B2 83 125 KX125 MOTOCROSS
KX125-C1 84 125 KX125 MOTOCROSS
KX125-D1 85 125 KX125 MOTOCROSS
KX125-E1 86 125 KX125 MOTOCROSS
KX125-E2 87 125 KX125 MOTOCROSS
KLX250-A1 79 250 KLX250 OFF ROAD
KLX250-A2 80 250 KLX250 OFF ROAD
KX250-A5 79 250 KX250 MOTOCROSS
KX250-A6 80 250 KX250 MOTOCROSS
KX250-A7 81 250 KX250 MOTOCROSS
KX250-B1 82 250 KX250 MOTOCROSS
KX250-C1 83 250 KX250 MOTOCROSS
KX250-C2 84 250 KX250 MOTOCROSS
KX250-D1 85 250 KX250 MOTOCROSS
KX250-D2 86 250 KX250 MOTOCROSS
KX250-E1 87 250 KX250 MOTOCROSS
KX420-A1 80 420 KX420 MOTOCROSS
KX420-A2 81 420 KX420 MOTOCROSS
KX500-A1 83 500 KX500 MOTOCROSS
KX500-A2 84 500 KX500 MOTOCROSS
KX500-B1 85 500 KX500 MOTOCROSS
KX500-B2 86 500 KX500 MOTOCROSS
KX500-C1 87 500 KX500 MOTOCROSS