Stage 3 Jet Kit Questions

[TonyW]

I've ordered a Factory Pro stage 3 jet kit. The Factory Pro rep said that, in addition to the K&N air filter that comes with this kit, that I may need an air filter for a crankcase vent. Does this make sense to anyone?

Also, Factory Pro says that a new exhaust is not required for this kit (although air filter is).  Any opinions on this?

Thanks, T_

[Hi-T]

Stage 3 eehhh??  I'm thinking that it might be overkill.  You need the stage three to keep up with the exhaust... you're allowing the bike more air and fuel to get into the engine but it can't get out fast enough for a real improvement in performance.  No, you don't need the exhaust for it to work but you will for it to work well.

And... you could get the same improvement by buying the jets and filter individually (Do it yourself - DIY Jet kit for $40).

[Gisser]

On your stock bike, the crankcase hose vents into the airbox.  If the airbox is removed it's necessary to connect a filter to said hose to prevent crap from being sucked into the crankcase via vacuum pulse.

Contrary to popular belief, increasing the airflow through the intake and exhaust do not lean out the carburetion.  Stage 3 jetting is to compensate for the weakened fuel draw caused by the increase in air pressure in the carb venturi and main air jet that occur when the airbox is removed.  Nothing to do with the pipe.  

That's not to say a pipe isn't good for a horsepower or two.

[V8Pinto]

Contrary to popular belief, increasing the airflow through the intake and exhaust do not lean out the carburetion.  Stage 3 jetting is to compensate for the weakened fuel draw caused by the increase in air pressure in the carb venturi and main air jet that occur when the airbox is removed.  Nothing to do with the pipe.  

This is the best quote I have seen on this board.  Everybody should read this three times, then harken back to high school physics class.  There is no such thing as "vaccuum".  There is pressure differential.  Less restriction at the air filter means the engine is not creating the hole of negative pressure (relative to atmosphere) because it cannot breathe through the air filter.  Sort of like if you tried to inhale through a 2 liter pepsi bottle.  It would want to collapse.  If you made a small hole in it, you would have more pressure (less vaccuum) inside the pepsi bottle.  If there is less difference in pressure between the atmosphere and the inside of the intake tract, the atmosphere does not "push" as much fuel through the vent tube, through the jet, and into the intake tract.  Increase the jet size to get that fuel back.

This of course ignores the velocity aspect of things but it is true nonetheless.  

Shane
306 N2O Pinto

[TonyW]

Thanks All!  

Any suggestions on a filter to put on the crankcase hose?

My reasoning behind my decision for stage 3 went something like this: if I'm gonna muck around with the carbs I might as well pay for a performance filter and go whole hog -- this especially as Factory assures me I don't need a new exhaust pipe.  

Thought of DIY jets + filter, but since the most I've done with combustion engines is replace oil and plug in a lawnmower, I decided to pay up to Factory's instructions and hand holding.