Did a search through some threads in relation to this problem but thought I'd post it here anyway to see if I get any different responses
I've got a 2011 WRF 450 which is stock standard, no mods at all yet (Had the throttle stop etc removed) - only 150KMs on it and just had it's first service.
I purchased a new FMF Powercore 4 slip on muffler and put it on - bike started cold with no choke pretty easy - normally I need to put the choke on and takes a few kicks. The bike does not start if I have the choke on either..
Bike sounds good!
Once it warms up after about 2 minutes and I crack the throttle it backfires so damn loud - it also shoots flames out of the exhaust that reach up to a foot long. Bike idles fine with no flames - mid and high revs it backfires when I release the throttle.
Here's a video of the flames - although it didn't seem to backfire when I recorded it. I turned the lights out so the flame could be seen.
I've ordered a JD Jet kit which has just arrived so I'm going to mess with that later in the week. I recall there being a thread on here once where everyone posted there mods and jetting specs? is that still around? I couldn't find it.
I'm going to go with the problem being the jetting but would like your opinion too please
Edited by xsmilinx, 10 August 2012 - 03:32 AM.