Dumb Jetting Question

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Feb 9, 2007
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#1
I pulled this straight from the Canadian Dave page:

1995-2001 KDX200

Stock -Run the stock R1174K jet needle in the second from the top clip position, 45 pilot jet, 155 main jet and fine-tune the pilot circuit using the air screw.

With a performance pipe/expansion chamber, the air box lid removed and the stock or a performance silencer run a 42/45 pilot, R1174K jet needle in the mid clip position, a 152/155 main jet fine tune the pilot circuit using the air screw.


The above seems to imply that with a pipe and airbox mod, I should consider smaller jets (ie with mods maybe use a 42 pilot instead of a 45 and a 152 main instead of a 155).


Question:

Why would I want smaller sized jets with a performance pipe and opened up airbox? It would seem to me (apparently incorrectly) that a performance pipe and modded airbox would result in more air flow, such that I would actually want MORE gas to maintain the same air/fuel ratio. To get more gas, don't I actually want jets with higher (not lower) numbers?

Put another way, would not modding the airbox and putting on a pipe, all else equal, tend to make the bike run less rich than it would otherwise?

Thanks, and sorry if this is dumb.

Brent
 

IndyMX

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#2
Considering for most conditions, bikes ship from the factory way too rich, you will would need to lean it out a bit.
 
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#3
bmcd308 said:
I pulled this straight from the Canadian Dave page:

1995-2001 KDX200

Stock -Run the stock R1174K jet needle in the second from the top clip position, 45 pilot jet, 155 main jet and fine-tune the pilot circuit using the air screw.

With a performance pipe/expansion chamber, the air box lid removed and the stock or a performance silencer run a 42/45 pilot, R1174K jet needle in the mid clip position, a 152/155 main jet fine tune the pilot circuit using the air screw.


The above seems to imply that with a pipe and airbox mod, I should consider smaller jets (ie with mods maybe use a 42 pilot instead of a 45 and a 152 main instead of a 155).


Question:

Why would I want smaller sized jets with a performance pipe and opened up airbox? It would seem to me (apparently incorrectly) that a performance pipe and modded airbox would result in more air flow, such that I would actually want MORE gas to maintain the same air/fuel ratio. To get more gas, don't I actually want jets with higher (not lower) numbers?

Put another way, would not modding the airbox and putting on a pipe, all else equal, tend to make the bike run less rich than it would otherwise?

Thanks, and sorry if this is dumb.

Brent
Not a dumb question at all, your logic is spot on except if you will notice the lowered clip position has a tendency to make the recommendation more acceptable.