has anyone tried these outI know on a harley they make a little diffrence but just wondered if they are effective on the f4s. I found them on ebay for 34.00 so maybe a cheap power gain, and I guess the next question would be should I rejet the bike

 

Are you having backfires? If you already know that it needs rejetting, then do that first. If you still have backfires, then the block off plate could help w/ reducing the extra O2 in the system. But, there's no power gain.

 

thats all I needed to know bike runs great just looking for that extra little gain other than the normal jet kit and headers