We sell a high performance UNI air filter for the GS250, 2 stage run dry foam type. We recommend re-jetting and can supply you with jets. Do not cap off the crankcase breather, you'll build up pressure and toxic fumes in the bottom end and will damage your engine over time. If you've ever noticed there's a small clear resovior on the air-box, its there to collect the oil from the breather. If you go with an aftermarket air-filter, you need to create a new resovior out of a small platic bottle, route the crankcase breather here and empty the bottle periodically as you would the stock resovior.
John
Economy Cycle
