finally my k&n replcement is in. now i know im gettin a new seat for x-mas to. yay. so k&n with a cobra f1r slip-on exauhst. do in need to rejet. i mean is absolutly necessary?

Not absolutly, no. It will help, but since it's a slip-on, it won't be that big of a deal. The K&N will lean the bike up a bit, and the exaust will richen it up a bit also. If it were a full system, it's good to jet.

 -Anti

Quote from: The AntibodyNot absolutly, no. It will help, but since it's a slip-on, it won't be that big of a deal. The K&N will lean the bike up a bit, but the exaust will richen it up a bit also. If it were a full system, it's good to jet.

 -Anti

How can an exhaust "richen" it up?  :dunno:
Any increase in air flow through the engine will lean it out, either by air filter or exhaust. If you aren't going to re-jet then why even bother spending money on performance parts? I would re-jet!

Oops. my bad. I didn't mean that. Yeah, both lean it out. It's already a bit lean stock. Jet kit = good.

I feel like I'm taking crazy pills.

 -Anti  :dunno:

QuoteHow can an exhaust "richen" it up?  
Any increase in air flow through the engine will lean it out, either by air filter or exhaust.

"How can an exhaust `richen' it up?"

In theory (Bernoulli effect), jetting naturally tends to become richer as airflow through the carb venturi increases.  I do believe this holds true for mods downstream of the carbs such as aftermarket pipes.  The purpose of going up 1 size in main jet would be to cover holes in the powerband that hi-flo pipes create by eliminating useful backpressure.

Also, best not to confuse the GS's EPA strangled pilot jetting for lean jetting overall as the GS is known for spot on jetting in the upper range  
straight off the showroom floor.  Another point to consider is that CV carbs are self-correcting to changes in airflow to a large extent.

Changes to airflow upstream of the carbs (pod filters) increases airpressure throughout the intake tract which (in accordance with the Bernoulli principle) decreases fuel draw making rejetting a necessity.  Note that big jets do not equal big fuel draw or big power.

I mean, yeah, the pipe riches it up...... um yeah. HEHE I'm lost now. Maybe an aftermarket exaust is just magical. Ooooo, something to think about.

 -Anti  

Less exhaust restriction = leaner burn (aftermarket exhaust)
Less intake restriction = leaner burn (aftermarket filter)

Not arguable.  Proven for dacades.  End of discussion.  Rejetting will balance things back out.

Thanks Dad. Isn't it great when John puts his foot down?

 -Anti