@lanny3 , Lanny, How well did you clean the oil in the filter box, did you replace the oil drenched filter as it could be clogged choking the engine, also make sure the clutch and belt are clean of the oil. There are a few things that could cause your engine to bog. Bad fuel, fuel line collapsing(pinched), clogged fuel filter,dirty carburetor, fuel pump failing, Carbs out of adjustment, bad plug wire, wires/plugs shorting out/loosing connection, weak coil/ignition box/CDI, wrong/fouled plug, vacuum leaks/bad crank seal, stick valve/reed, etc. I will post a link below to the service manual which may aid in your diagnosing and repair and a 2nd link to a forum diagnosing your issue. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://coodie.com/polaris/1999-Polaris-Service-Manual.pdf
http://www.snowest.com/forum/archive/index.php/t-127644.html