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.
Using pod-type air filters
Q: I own a 1980 Suzuki GS450, which I bought from a guy who had started to “rehab” the bike. He installed pod filters on the carbs. While they look good, he changed nothing on the carb setup, resulting in a typical flat spot in midrange on/off throttle response. He said he threw away the original air filter and airbox, which he said taught him not to throw away original parts from an older bike. The bike has the original Mikuni BS34s carbs, and due to EPA regs, the air screw is set and capped from the factory. I’m not looking to make a screamer out of this bike, but I like the look of the pod filters. If I pull the plastic cap off the air screw and tighten it up a little, wouldn’t I be able to get back to the correct air/fuel mix without re-jetting the carburetors? — Eric/Cincinnati
A: Your problem’s probably not in the air/fuel mixture. The GS450 had a reputation for poor carburetion when new, running very lean right out of the box (see A 400 on Steroids: Suzuki GS450) — and those pod filters are likely just making it worse. I’ve never been inside a GS450 carb, but Suzuki supposedly installed 1mm shims above the slide needles, lowering them for a leaner mixture. Removing the shims may be all that’s needed to fix the stumble. If that doesn’t fix it to your satisfaction, MikesXS.net has richer needle and needle jet setups for that carburetor. I can’t offer any exact specifications; those will vary with altitude, fuel type, engine condition, etc., and have to be found by experimentation with your machine. MC