Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Q: I just bought a 1969 B44 BSA 441 Shooting Star. My initial ride on the bike was fine, but I was getting just a bit of a pop out of the exhaust when I roll off the throttle. I ran it for a while, hauled it home, and then took it for another ride. This time it started popping a lot every time the throttle was shut. This is my first British bike (except for an AJS Stormer motocross bike I rode in the ‘70s), so I have no experience with them. Before I start fiddling about, I figured I should ask an expert. Does this sound like a timing problem? Or do I have fueling issues? The bike appears to be completely stock. It’s using an Amal carb, and the bike has about 9,000 miles on it. — Rod Jackson/via email
A: Popping on the overrun could be due to a too lean idle mixture from the carburetor. You can test this by turning the idle mixture screw in one-quarter to one-half a turn to richen the mixture. You may have to adjust the throttle speed screw to get your steady idle back. Then go for a ride and see if things are better. Another possibility is an exhaust leak at the head to exhaust pipe junction. Air sucked in there will cause popping in the tailpipe, too. MC