I have a 2005 Honda Rubicon with 2900 mi.Latley it sems to lack power(It works & pulls but doesn't have the same "Omffh" it once did.This problem started all of a sudden one day after filling up with regular gas.There is a noise that sounds like spark knock when the engine is pulling or working harder than normal.This noise happens when you give it full throttle. Also the spark arrestor causes a chirping sound when the throttls is applyed.I've removed & cleaned it but it still chirps.Could these 2 problems be tied tohether

 

The chirping sound can be rid of by removing the spark arester and cutting the bell off the end of it ( the end that points into the muffler). If you look at it when removed, the bell has a split in it. This split is where the whistle is coming from. Removing the belled end will not affect the performance of your Rubicon.
The power loss could be as simple as valve adjustment, I would gamble that the decompressor on the camshaft has gone bad and is partially holding a valve open

----- Gimpster -----