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Have to rejet?

867 views 6 replies 5 participants last post by  N1ckel 
#1 ·
This feels like an old topic but j don't think I've seen a definitive answer. I've got pretty damn good at rejetting, shims, needles, pilots etc, and got the bike running nicely.

I recently acquired a used set of Predators to upgrade from the TORS. The TORS are already more open than stock pipes, and Preds more open still.

The question is, do I have to rejet? Just because the Preds might allow more output, surely the engine won't push more than I give it? Does a mixture become more lean just by putting more open pipes with no other changes? So do I go up from my 120's, bearing in mind 42's, Thrux needles with one shim? (I know, but it's where the bike is happiest... ;) )
 
#2 ·
If you haven't made any changes to the intake side of your engine, I doubt that you'll need to rejet just because of the new mufflers - the bottleneck will be the intake, and improving exhaust flow won't make a significant difference. The answer will also depend, I guess, on whether you are a bit rich or a bit lean right now. You might want to think about removing the snorkle and the air box restrictor plate. More information on the various mods/changes to your bike would get you some better advice.
 
#3 ·
Agree with Bill…however….since you said this...

"I've got pretty damn good at rejetting, shims, needles, pilots etc, and got the bike running nicely."

Sounds to me like the prime time to ditch the airbox alltogether. The 790's start to run w/o the airbox and mufflers like the predators.:smile2::smile2:
 
#5 ·
Yes snorkel gone and filter cover carved, but airbox restrictive still in place. Yes they are loud lol.. I've put mini baffles in, which I cut in half and bent the flanges in, so there's just the slightest bit of baffling, which just takes the edge off the noise without killing it.
 
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