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Another Jetting Thread: 2005 WR450 JD Jetting

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Hey guys. I finally got my WR fired up after a carb cleaning and JD Jetting kit installed. Looking for some feedback on next steps to get my setup dialed in. I set up the carb per the JD instructions, but while attempting to set the fuel screw per the forum instructions (starting at two turns out @ 1500 RPM), I could turn the screw in completely and the idle increased and idled just fine completely closed. Based on my mods (mainly the opened airbox and Q4 silencer), I was expecting I'd be running lean, but as I understand the fuel screw instructions, I should actually go to a leaner pilot jet since I idle just fine with the screw fully in.

I also have a JD fuel screw, and the instructions indicate "if the fuel screw has no effect or idles faster when turned closed, set the screw at 1 turn out or consider using a smaller pilot jet."

Idle is smooth. No popping with throttle blips. No hanging/dropping idle with blips. I was able to run the bike around my yard for 15 minutes to get it hot, but I don't have the space to really open it up, so I can't comment on anything other than the idle performance.

So, I guess what I'm trying confirm whether or not I should make a change (PJ or otherwise), if something seems amiss based on my setup, or if I should just run it this way for a while and monitor performance.

Here's the details based on the jetting database format:

Year: 2005

Model (400 - 426 - 450): WR450F

Cam Timing (WR/YZ): WR

Main jet: 170 (from JD Kit)

Pilot Jet: #45 (installed from JD kit)

PAJ: #80 (stock)

Leak Jet: #50 (stock)

Starter Jet: #65 (stock)

Fuel screw (turns out): 1 turn out on JD FCR fuel screw (per JD instructions). Idle increases as screw turned in.

Needle Model/Clip position: JD Red / 4 (per JD instructions)

Grey Wire Mod (Y/N): Y

TPS Connected (Y/N): Y

Airbox Snorkel/Lid (on or off): Snorkel removed, opened airbox

AIS Removed (Y/N): Y

Airfilter Brand: UNI filter

Exhaust Brand: FMF Q4

Average Altitude: 950ft

Average Temperature: 75F

Average Humidity: 65%



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You adjust the fuel screw for idle speed, not turns.

Hot motor, put the fuel screw at 1 turn, then lower the idle as low as it will go.

Now turn the fuel screw out to raise the idle. Should be about 1.5.

You need a smaller leak jet, and a APump upgrade, both the linkage spring and the diaphragm system. That will give you good quick throttle response.




If you keep the ACV system, the fuel screw adjustment will always be somewhat random.

If you block it off (remove the floating piston and make a full blank gasket under the cover) then you will need to change the pilot air jet to 100.

Then the pilot circuit will have no 'overriding' features that make tuning it difficult.

Everything else seems fine, but the 170 might be to big. If at wide open throttle, under load in 4th or 5th, backing off the throttle a bit makes it run better, then it is too big.


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