Motorcycle Classics Blogs > Tech Corner

Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


1977 Yamaha XS650D

Motorcycle Classics tech expert Keith Fellenstein

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.

Yamaha intake question

Q: I’m in the process of restoring two 1977 Yamaha XS650Ds. Upon attempting to synchronize the carburetors on one of the bikes, I noticed that there are rubber plugs or “reducers” going from the air filters to the intake. There is nothing in the Clymer service manual that shows these. My question is, what do they do and are they needed? Do I leave them in when I connect my vacuum gauges? — Ron Wandler/via email

A: I’m not sure this is the part you’re talking about, but there are intake silencers that fit inside the air cleaner elements that are specific to the D model and not found in the E and F model. Their purpose is to quiet down the intake roar. This was done to reduce the overall noise level the bike produced from intake and exhaust noise. Since they were eliminated on the models following yours you can probably remove them with no ill effect other than that satisfying sound you get when you open the throttle. If you take them both out it shouldn’t affect your synchronizing efforts. I’m guessing a previous owner of the bike that is missing them liked the intake sound without the silencers. MC