Good morning from sunny AZ. Just about given up on diagnosing this Mikuni BS40SS carb problem. It is on the sidecar tug bike,2002 MY. I understand it was removed by the PO because it didn't work right after he worked on it, believe it ran very rich. I think I found and corrected that problem. #4 washers replacing the nylon spacer had a oversize OD so the needle was raised very high, because it didn't allow the needle to sit in the recess. It starts and runs fine, but won't go past about 1/2 engine RPM. Is just flat at that point. Ihave had the diaphram and slide assembly out and checked it for proper installation, no visible holes in the diaphram, slide moves up and down freely, and holes are lined up in the needle retainer plate. It acts like the slide isn't raising at all. I did bring the AMAL carb that was on it but the mileage was in the 30's with it and as I am not at home with all my tools, changing it back is going to be a challenge. I modified a metric allen wrench to R&R the intake manifold screws and aparently did not bring it with me. The questions are: what else could the PO have done to cause this symptom that I missed? Will the OE intake flange work with the AMAL carb? if I decide to change back to it and work on rejetting it. Weather is nice (high 70's days) and surface street are just right for scootin'. Got 60 MPG on last tank of the bagger as speeds were mostly 45 MPH or less. Did 130 before hitting reserve and then only took 2.1 Gal. Thanks for any input or ideas. Max.

Agree With Verslagen....  check the jets... BUT,  look at what size jets are in there.  Mabe the PO didn't put it back together correctly.....

I think Greg has sizes in the Tech section somewhere.   Or maybe it was SavageWahine.....