Fmf powercore 4 + header
 

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Just got a 09 250s, came with stock exhaust on the bike and a powercore 4 pipe and header too. Buddy said it melted a hole in the airbox and he had to replace it thats why he took it off and went back to stock. Found in searches that some peoples fit funny but not melting anything. Anyone heard of this? Could i wrap the pipe and maybe that could help? Stock looks like it sits pretty close too. Necessary to get the jet kit if i do put it on the bike? Thanks!

How bout you put it on and don't let it melt your airbox ? Whether you melt your airbox, or not, is up to you.

Wrap? Help? No! - it'll come into direct contact with the airbox, or close what little gap there is - things to be avoided..

You must install the system successfully enough to avoid melting the airbox.
If you can't find proper clearance during install, you will need to provide the "correction" to the system. Tractor jack handles, crowbars, 6' pry bars, Vices to allow bending mounting flanges, etc, will do the trick - to bend and tweak the system enough to provide the needed clearance.

Better yet - do both. My FMF system could be installed with good clearances, I tweaked it to provide even more..

Who knows what has or hasn't been done to your '09's carb.. But with a stock carb and airbox, no rejetting is needed as no real increase in power levels will occur. You begin to unleash more power with a snorkle delete and DJ kit (2152 or 2206). Go all the way to about 24hp with lidless airbox and the DJ144/1N carb setup - for this, read the correct link below.