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Leak jet/AP

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Leak jet Check valve.

Oservations have been made regarding the Boyesen quick shot and its second ports ability to be effective. Some felt that the check valve was the limiting factor. Now after veiwing the pic's of the 07 CRF450 carb I can see the check valve has been removed all together and began to wonder. Any thoughts out there??

Has anyone else out there tested a mod to remove or modify this check valve. Based on the number of posts I read out there I gathered this would be an important test. Thanks to James Dean for the pic's.


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Join Date: Apr 2000

Location: Washington

Posts: 4,355

2007 CRF450R Carburetor Updates

The 2007 CRF450R has some major changes to the bigger, 41mm FCR carburetor. These updates mostly focus on the accelerator pump cover and linkage that works the accelerator pump.

--The new carburetor has a revised accelerator pump linkage that "pushes" the pump diaphragm with more pressure, unlike the flexible "spring" linkages of past years. The pump timing adjustment screw now turns OUTWARDS to add freeplay, opposite from past years pump timing screw.

--There is a new cam and roller arrangement that determines the pump stroke instead of a bottoming rivet on the diaphragm. Therefore, the diaphragm is new and lacks a bottoming stud.

--The pump now has a fuel inlet on the BOTTOM of the cover. The pump's inlet check valve is located IN THE COVER, and no longer in the float bowl.

What this results in is a pump that gives an immediate, stronger squirt of fuel, which finishes it's full stroke in the first half of the throttle range. The pump force is comparable to a wired or stiffly banded 2006 linkage, with a stroke limited volume.

--The carburetor now has a different needle, with only 5 clip position, and new retainer bolt in the slide. The needle is longer and cannot fall thru the slide when the clip is removed. The retainer is more like a bolt with hex head instead of an Allen screw. The larger size requires a new top cover for the carburetor also.

Pilot jet- #42

Pilot air- #100

Needle- NJYR #3

Main jet- #178

Accelerator Pump Leak Jet- #50

See pictures at-



Linkage- 2006 (Left) - 2007 (Right)


Linkage Cam Roller-


Pump Covers- 2007 (Left) - 2006 (Right)



Pump Diaphragms- 2003-6 (long stud), 2002 (shorter stud), 2007 (flat rivet)


Carburetor Needles and Retainers-



'06 450XC

'05 CRF450X

'04 CRF250R

Last edited by James

_Dean : 08-05-2006 at 09:32 PM.

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