Gonzo, Thats exactly right. The set screw on the accelerator pump is the screw that you install when you perform the BK Mod. This allows you to adjust the amount (Duration) of fuel being squirted into the carb when you twist the throttle. From factory, the squirt ussually last 3-8 seconds. After the BK MOD is complete, you tune the squirt down to .3 -.5 of a second. This is the main reason these bikes bog
from factory. They are getting WAY too much fuel at a inconsistant rate. If the mechanic was talking about an allready existing screw on the carb then he was talking about the Slide Timming Screw. This screw also affects the bog however it is not the primary reason. When you twist the throttle the accelerator pump squirts fuel into the carb and in most cases from factory the fuel hits the slide thus causing a bog. The correct setting should be: While looking down the carb, twist the throttle slowly and look at the accelerator jet. When the slide starts to rise the fuel will begin to flow out of the accelerator jet. The flow should JUST miss the bottom of the slide. If you see the slide getting wet, fine tune it some more. Also, while looking down the carb, twist the throttle wide open and hold it. Count how long your squirt is. Again, it's probably 3-8 seconds where it should be a fraction of that. I'm sure you guys know this but if you don't this BK Mod came from Brian Kinney, Tim Ferry's mechanic hence the word "BK". If Tim is running this mod on his Factory Yamaha
you know it RIPS!!! Also, this mod shouldn't effect the warrenty. It's no worse than adding an after market pipe. If you do have problems and have to take the bike in for warrenty work, take the mod out. It can come out in seconds!!