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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


1994 BMW R1100RS Ethanol Troubles

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, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Ethanol troubles

Q: As it’s very difficult to find ethanol-free gasoline these days, I’m curious as to your thoughts on the long-term effects of that concoction on daily riders? My last experience was with my not exactly vintage 1994 BMW R1100RS. Through 65,000 miles the effects of the less-than-ideal fuel was noticeable, with ventures into the tank to change out fuel filters and rubber hoses. We hear of additives to calm the effects, including Stabil and the like, but nothing is very confidence-inspiring. This bike was injected, so the injectors were a concern, along with every gasket and plastic part contacting the fuel. Then there is the “coat-the-tank” exercise that is commonly temporary and necessarily repeatable for steel-tanked bikes. So while I’d love to go back to the Honda CB500 four of my earlier days, I have my doubts. — Terry Meyers/via email

A: While it’s certain that ethanol in gasoline damages fiberglass tanks, the effects on the rest of the fuel system are more subtle. If your bike has a fiberglass tank, you should stay away from gasohol, as the ethanol dissolves fiberglass. Ask anyone with a vintage Bultaco and you’re sure to get an earful. It is becoming more difficult to get ethanol-free gasoline. Websites such as pure-gas.org show where you can buy ethanol-free gas in the U.S. A more expensive option is aviation gas, assuming the local airport will sell it to you. It may be technically illegal, as I don’t think avgas has highway taxes added to the price. The problem there is that you can’t travel and be certain of a good supply. That brings up my modus operandi, which is that any gas being burned right now is good enough. It’s when you let it sit in the tank for any length of time that problems stack up. You should make sure the fuel lines and any rubber parts in the carburetors or fuel system are alcohol resistant. For storage, I usually try to not leave a partially full tank of any fuel; the extra air space above the fuel invites condensation and rust. An ethanol treatment additive can help with the long-term effects of storage, too. MC