Leaderboard

I'd get 3 bungs put in the pipe myself. Like this. A single one past the last collector and one each just past the other collectors. Then you can tune each set individually if you want. Just my thoughts on the matter.

Absolutely! Mine was a leaky mess as is. I yanked that BEFORE I did the MTB and my idle changed a touch, which tells me it wasn't exactly working per spec anyway. You can argue about flapper mods, and I can see both sides, but I will ALWAYS recommend yanking the PAIR, regardless. But if it's letting fresh air in you straight up won't get the right readings. Probably run rich and fluctuate based on how you're riding and how much air those valves are leaking in.

The 4.9 version has a smaller plug that is completely oval where the 4.2 is bigger and has a flat side to the oval. I use 4.9's on the VFR and also on the MV F3 I work on. Also, just make sure that if you are sealing the headers up stream of the O2 sensor, use a sealant that is O2 sensor safe. some HT silicones are not. On that note, making sure that there are no air leaks in to the headers, up stream AND down stream of the sensor is extremely important in getting the best and most accurate results. Make sure that the PAIR system is completely removed and well sealed.

I got mine cheaply at Harbor Freight.