It is in the middle of the block. Under left front wheel look for wire and reach in with left hand. Wire/socket to connect to plug points up. I found it but cannot get an answer on plug wrench size. Good Luck had the same problem use the tools under the seat a liitle akward but gets the job done
NGK Plug DPR8EA9
on the motor lol
0.031 to 0.035"
No, you do not have to .....
part #: NGKDPR8EA-9
NGK BR9EG is the correct plug for a 2001 Yamaha YZ 125
Spark Plug fouling is pretty common.
.030-.040
Ngk cr9e
From the 98-01 service manual - .03-.04 inch (.8-.9mm)
NGK plug BP4HS - Gap for PW 50 is 0.6mm.
The 2004 Viper Yamaha spark plug gap is .018. Most spark plugs will be pre-gapped by the spark plug manufacturer.