I just rebuilt my engine. (92 Shee) She sounds great except for the backfire. What would cause a backfire. I believe the carbs are sinq. I did jet the carbs to 290. I have fmf pipes and silencers, boysen rad valve with carbon fiber reeds, k&n filter with precharger(outerwear). I think that is about all of the engine mods. So what is you take on that? Oh yea with Wiseco piston and rings.

 

The rad valve is unique cause for some reason the manufacture (boysen) suggests that you rejet down a few jet sizes on the main, it's possible your running too rich cause of this so I would drop to a 260 main and check the spark plug for a good color, also b4 you do this check your plug and it will probley be black(rich) wich could most likley be the reason for your backfireing then lower your main and put the needle in the third position(stock) and adjust your air feul mix until the whole rev range is smooth remember it's easier to start with the main and work your way down, I have a rad valve and had to lower my main jet and place the clip back to the stock position to get the best performance. this happened to my bike cause I got the pipe first went up to a 280 main and one up on my clip but after installing the rad valve I ended up going to a stock clip position and down to a 260 main....
hoped this helped??

 

Actually this helped alot.. I was hopeing someone has done this mod to their bike and has fixed the error. With all of the mods prior to the Rad Valve I was up around 290.. And the directions in the box to the Rad Valve said to jet down 2-4 sizes. I just rebuilt the motor and so many things were running through my mind of what could be wrong with the bike. So you think that if I rejet the carbs to 260 that it would stop backfiring? I think the clip is still in the stock position. I haven't even broke the motor in yet. I heard the backfire and just shut it down. So I will try the rejet and let you know how it worked. Thanx
Mike