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Old 03-03-2007, 01:43 PM   #5
potatoho OP
Cheese and Rice!
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Joined: Aug 2004
Location: Sea-level
Oddometer: 4,706
Today I rode on/off road to test things out. The strange AFR dips are occuring only on the street and I finally found a correlation. It only happens beyond a certain speed and when I'm on windy streets. Noting the location of my O2 sensor, I'm thinking that what I'm seeing is a seal leak in my exhaust. Either the joint directly before the sensor or the header/cylinder joint.

As a side note, I removed the dial-a-jet and I haven't noticed any change in readings. It appears that my install location is poor, because I know that these things do affect the mixture quite a lot when installed directly on the carb. Not sure when/if I will reinstall. I actually do believe it was supplying some mix, but it felt like it was only doing it during extreme vaccuum, such as when decelerating. I notice more AFR dip / popping during deceleration than before. That could also be an indication of my exhaust seal deteriorating.

So now, I'm running a stock BST40 (47.5 pilot, 155 main, 2.5 clip position, stock float level). I have an ids2 quiet core w/ 10 discs. Stock airbox side cover, snorkel removed and opening enlarged towards the front. I think it's pretty darn quiet. 2.5 clip is evidently the lowest you can sit this needle in this carb. At clip 2 I was getting an extreme 1/8 throttle lean dip.

It runs well. I can quickly twist the throttle wide open from a low idle and it revs. My idle is extremely low, just for giggles. I don't have the auto-decomp on my cam so I was able to set it to like putt putt putt. Off-idle torque is good, power is electric. No bogs so far on the whoops. Power is not super good, but it's the most this bike has had so far.

The exhaust leak, or whatever it is, is causing a noticeable artifact in the running. When the AFR reads solid, the bike is running smoothly, but when it starts jumping around then it has some vibes and an audible distortion to the exhaust tone. At first I thought it was some airbox vortex due to my removal of the snorkel, and it still could be, but now I think it is the exhaust.

My mileage is currently 45mpg.
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