Don 1

The later DT125R's have restrictions in the exhaust, the CDI and speedo(linked to the CDI). Remove the restrictors from the front pipe by cutting the pipe in two at the main weld joint about 12 inches from where it bolts to the cylinder. See here Get a old CDI from an earlier model (1989 would be best, 1990-92 next). Simply removing the exhaust "washers" from a 1999- bike just isn't worth the effort. get an less restricted CDI too. For earlier bikes without the YPVS controller fitted as default, remove the exhaust washer from the neck of the front pipe and ensure the power valve is pegged in the "fully open" position. Consider an earlier CDI unit too.