I rebuilt the carbs on my 2001 gp1200r, and was surprised to find they had no high and low speed mixture control screws, just blocked off ports, marked H and L. The carb kit included o rings for the screws, and showed the screws on the schematic, but no screws on the carb. What gives? Also, for $50 a kit, you'd think micuni could include a welch plug replacement so you could remove the one on the carb and clean below it, my $9 rebuild kit for my husky chainsaw included the welch plugs, pretty lame

The mixture adjustment screws are blocked for two reasons. First and foremost to comply with emissions requirements. Secondly, they're set on a flow bench. Meaning the carbs are adjusted before they're installed on the engine. They don't want you messing with them afterwards.

To access the mixture adjustment screws drill a pilot hole in the center of the plug about 1/4~3/8" deep. They're brass so go easy. Then install a self tapping screw. Use a pair of vise grips to pull the plugs out.

IMPORTANT NOTE: Make sure you document the original settings before adjusting them. They will not be the same from one carb to the next. For the most part you need to stay within that window of difference when adjusting them. That is unless you modify the engine (exhaust, heads, porting, etc). Then you can go the normal route of dialing in the carbs.


With pwc carbs the 'welch plug' is used to cover passages that are machined unlike other carbs where there are actual jets.

thanks for the info. If I drill out the caps, how is the screw adjusted, with an allen head or slotted screwdriver. The reason I'm asking is that I removed the cat converter on a otherwise stock 2001 GP1200R and would like to richen things up a bit. The plugs are light tan after pulling hard, I would like a little more color in them, or is light tan ok for this machine? thanks in advance

No problem. You will use a small, narrow flat head screw driver. Which can be difficult when trying to adjust the low speed screws. We offer what are known as 'T-handles'.



They make adjusting the carbs a whole lot easier. For your craft you will need the RY1220 set.