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 your subject.
Take off the Aftermarket Carbs on a Suzuki GR650?
Q: I’ve read your blogs and enjoy your knowledge of older bikes. I don’t know if you have worked much with Suzuki GR650 Tempters from the early Eighties. I hope so, because I’m in a quandary. I bought one, and it has aftermarket carbs and a K&N airbox instead of the stock carbs and air filter. It runs lean, but it’s in really great condition otherwise. I have thought about taking these carbs off and selling them and replacing them, but I’ve had trouble finding stock GR650 carbs in good condition. Have you ever heard about this kind of bike and what other carbs might work as a substitution for the stock carbs? I can block up the holes that go straight to the valves from the dirt bike carb, and it might be OK, but overall I’d just rather have a carb that’s a better match for this bike. — Jason Ritchie/via email
A: I’ve not had one of these in the shop, so I had to do a little research to find what you were talking about. It seems Suzuki added a port to these bikes to swirl the air/fuel mixture as it entered the combustion chamber in an attempt to further atomize the fuel. The carburetors for your bike had an additional hose that conducted metered fuel to the swirl port. I doubt those carbs are easily found these days. You can probably close off the swirl ports and just use the main carburetor ports. I wonder if the previous owner made the change because of the difficulty in getting parts? I think if you block off the ports you’ll be fine. If you have the time and the patience, you can work on the jetting, if needed. Other than losing the original look, the bike should run fine if the carbs are correctly set up. MC