Blown76mav Posted September 15, 2013 Report Share Posted September 15, 2013 Ok first I'm new to the 2 stroke world. Always been a 4 stroke guy until my brother bought a banshee then I rode it. I went out and bought one and being a car guy this is all new to me. The guy I bought it from said it just needed to be jetted for the big bore kit. It runs great until you go full throttle then it seems to fall flat. Plugs are gray and dry. a little about the Banshee Its a 1999, suppose to be a 421 ( but I'm not sure if it isn't a 392) Athena Jugs and heads Not sure how to tell the difference between the 421 and 392 without taking it apart. It has the stock Mikuni carbs with a 280 main jet (this is where it runs best). The sprocket is a 13 tooth on the engine Exhaust is FMF Fatty Gold's It has carbon fiber reeds on stock cages and new carb boots K&N air filter with stock air box with vents and drilled lid. Ok so I changed the main jet out from a 270 to a 280 no difference in plug color but it did seem to run a little better. So I went up to a 290 main jet, now if I go wide open it bogs down and damn near dies. Plugs are still gray and dry. At 1/2 to 3/4 throttle the pipes seem to ping or gargle on and off. I really don't want to blow this thing up and could use the help. I do have some Mikuni 44 carbs with 240 jets but wasn't sure if those would work, they came with a parts banshee. Thanks Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted September 17, 2013 Report Share Posted September 17, 2013 First things first,pressure test that motor,check compression,make sure plug caps are good and all electrical checks out,you can chase your tail jetting a motor that has an air leak or electrical issue Quote Link to comment Share on other sites More sharing options...
kedge82 Posted September 18, 2013 Report Share Posted September 18, 2013 when a motor falls flat or loses all power when trying to achive full throotle and or cant make it through all gears because you can not reach the power band you are rich and need to drop mains once you achive wot with out probleoms ride and tehna djust needles from there leave needles alone until u get wot probleom fixed. but 280 seems pretty lean for what u are running so i assume you are at sea level? but all indications besides your plugs point to rich lean would run like raped ape Quote Link to comment Share on other sites More sharing options...
Blown76mav Posted September 18, 2013 Author Report Share Posted September 18, 2013 sorry, forgot to include that. I'm at 875 ft above sea level. Quote Link to comment Share on other sites More sharing options...
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