Home Forums 2-Cycle Racing KT100 SA Blueprint Reply To: KT100 SA Blueprint


Walt Gifford

Here we go, my favorite thing in the world, a box of junk parts.

Someone tried to bore this out for WKA and went too far at .960″ perfect for me though. I ground out the choke stop and lettering on the venturi then smoothed it out by hand with sandpaper and polished it with a scotchbrite muff spinning in the drill press.

I lapped the front, back and pumper surface with 600 grit and on the metering side I use a flat file and work around the nubs to take down any high spots. I also drilled the transition jet with a #55 drill to increase the fuel signal to the low needle.

Here’s something I always wanted to try. I opened up the pumper area on the crankcase side to the edge of the gasket seem. Maybe it will give the pump more effective area.

Now I mount the carby euro style and you have to do a couple of things for this. You have to drill new holes in the carb plate and you have to grind the cable arm to fit around the metering plate screw.

You also need to cut back some cooling fins on the cylinder to clear the throttle arm and you need a longer pulse tube. This allows me to comfortably reach the needles while driving. It also makes it easy to clean the screen or change pumpers at the track.

That’s it for now because it’s still freezing outside but I’ll get this thing on the no load dyno when the weather breaks. Hopefully the ground hog won’t see his shadow this year.


FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience