I have a 2008 yfz450 that I bought from a friend about two months ago it sat for about 4 years. I cleaned it up, carb rebuild, put hmf slip on on and it was running fine, took to on a small dune trip to Bowie az ran great for two days. The friend that sold it to me showed up and took it for a ride and said it's back firing which it did not do when I rode it. So ever since then about three weeks ago it back fires and bogs only when I stand up. If I sit down it runs great but standing immediately causes popping and poor running. I'm at a total loss as to why this is happening but think it's the seat pushing on a wire or switch/relay somewhere when I sit down. I thought it as the relay above the battery which is under the seat but today I started the bike and pulled the relay out and the bike did the same thing, ran fine when sitting but not standing or with the seat off. Messed with the plug that goes into the starter switch under the seat between the two fuses same thing. Does anyone know what this could possibly be? I do have the relay in order but don't know if this would be the issue as I thought it as only for sending power to the starter switch.