So ive been having problems with my 25det, where at (mostly) high rpms, the motor would stutter , kinda bog and sound like a subie at WOT.
pulled out coilpacks, cleaned the corosion out of the contacts and sanded the spring where it contacts the sparkplug and coilpack.Also added electrical tape to the coilpack underneath, to prevent arcing.
simple fix and only cost about 15$ in supplies
information was found at gtrcanada.com and skylines australia, and its worth a shot since many of our motors are a decade old already!
