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  #1  
Old 1 Week Ago
normanator27 normanator27 is offline
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Join Date: Jan 2013
Location: paradise
Posts: 1,112
Jetting a CRF450X

G'day,

I've bought a JD jetting kit for my crf450x. The kit says to use the stock pilot jet which according to the owners manual is a #45. Unfortunately the one in it is a 55. I also have a 42 but not a 45. Apart from knowing that the smaller the number the leaner the jet, I'm quite inexperienced with this type of thing. So my question is will the 42 be too lean? I can't find too much online about people using 42's, and not any in Oz.

I've also been advised to run the leanest JD setting which is red needle 3rd clip, 155 main with 45 pilot. From what I can gather most people in Oz are using the 165 main with 45 pilot. Any thoughts on this??

I'm on the coastal fringe on the NSW north coast.

FYI, the existing jetting settings were 55p 180 main with the stock needle on 3 clips up from the bottom. It went ok, but it starts easy when cold, then struggles to idle when hot (and stalls easily) and is a c#*t to start after stalling when hot.

Thanks in advance.
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  #2  
Old 1 Week Ago
Robbie Robbie is offline
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Join Date: Apr 2003
Location: Alice Springs
Posts: 925
Its been years since I played with X jetting but I ended up with stock pilot (screw adjustment only but don't recall how many turns) , 165 mj and a 450R needle on 3rd clip from top.600m altitude.
I had the airbox open, backfire screen removed, 450R header and a very open WB pipe and otherwise stock engine.
Played and tested the jetting quite a bit in temps from quite cold to very hot to get it good and didn't have to change anything once I was there .
180mj would be too rich, I tested with GPS various mains and ended up at 165, 162 was close but 2-3km/h less.
If you haven't already you can check the where the fuel screw is set at and try adjusting it in and see if it improves the idling and hot starting issues. sounds like you have the manual so if you aren't sure on the steps check there for details.
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  #3  
Old 1 Week Ago
andrew300 andrew300 is offline
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Join Date: Mar 2015
Location: Pomona
Posts: 28
As a general rule, manufacturers jet their bikes a little on the rich side, so it would probably be safe enough to at least try your #42 pilot and see how it goes.


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  #4  
Old 1 Week Ago
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Nutty Nutty is offline
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Join Date: Apr 2006
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No mention of PAJ and MAJ? Might as well go down the pub, if these two aren't correct, changing the PJ and MJ will do SFA.

Hint: The Keihin FCR-MX doesn't start on the PJ/PAJ. It has a totally separate starting air circuit and the starting fuel load is supplied by the SJ, NOT the PJ.

Also try to find a R&D powerpump, or at worst a Boyesen powerjet. also, check the squirt from the accelerator pump mast isn't hitting the bridge between the intake valves, it should shoot at the RHS valve stem.

A stock CRF450X with a pipe will rip your arms off when jetted by an expert. They had a serious motor.
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