by GP Kevo » Fri Jun 02, 2023 10:43 pm
Mikuni carbs are additive from the main jet down. So begin with the main jet. Have someone help you to mark 1/4, 1/2, 3/4 and WOT on the twist grip of the throttle. Then run the scooter through the gears and in third gear open the throttle to WOT, then reach over and switch the key off, killing the engine. You can then do a spark plug reading. Start with a too rich main jet, then work your way down. I started with a 400, way too rich on my ported TS1, then surprisingly got good color on a 360. Once you choose a main jet, then it's time to choose the needle and its position, using the same technique to check the plug at 1/4, 1/2, and 3/4 throttle to check jet needle jetting.
I've got to do the same thing on mine, as I've swapped the old carburetor out for a new one. Hopefully I can get up early enough to beat the beach traffic and do my runs on the Pacific Coast Highway.