New 2.5" heat risers are on Ebay, starting at $44.00 plus $16.00 shipping. 2.5" exhausts are probably too big for a 283, but they'll work OK. A 2" pipe provides better exhaust scavenging for a small engine, especially one with dual exhausts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!