Adjustable Accel Pump Options

Hick and others have either done this or are considering this modification:

The '00/'01 Flat CR carburetors have a some convenient adjustment features for the accelerator pump that the '98/'99 FCR's do not.

Under the black side cover on the carb is an adjustment screw to set the accel pump starting point. This is set to leave 1/2 to 1 turn of freeplay before the accel pump starts. You can feel this with your finger on the linkage by the light to firm tension on the springs when the pump starts. Turning the screw in DELAYS the pump starting point.

There is also a tab cast in the body for mounting a pump STOP. This will make an adjustable stop for the stroke on the actuating rod. After just having mounted a stop on my WR, here are a few suggestions. A 4mm x .7mm threaded bolt or screw fits very well. Use a 1/8" drill before tapping. Drill in the direction of the linkage cam. It will be clear where the bolt is to be mounted by the flat landing on the cover and casting. Cut the bolt to 18mm and use a 7/32 diam x .030 wire x 5/8 long spring to tension the bolt and hold it's position. File the end smooth where it rides on the cam/linkage. The black cover will need to be trimmed around the bolt and spring.

A stroke of 1.5mm is made at about 1 1/2 turns out with this setup. This is close to what the P-38 Lightning is made to produce.


The stock '00WR uses a 3mm stroke which is about 3 turns for comparison.



For us unlucky owners of 98/99's, is our only option the P-38?


'99 WZ with all YZ mods, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, forked over by Pro-Action, OEM YZ tank and IMS seat.

i'll say my bit & i'm sure JD will add his.

the problem of stopping the APJ can be tackled by twisting the pronged leg(as clarke mentioned)the system is incredibly crude. if a tickle of APJ is the ultimate answer then we '99ers are in trouble.

if however no APJ is involved we have no disadvantage at all & infact those of us who never bought the P38 have saved a lot of money beacause they'll be worth &%$#@!all secondhand.

i also believe you'll find that ideally there should be a delay in the START of these things. quite frankly we haven't got a hope in hell of getting that right.

why don't you hope, with me, that no APJ is required!


For the '98/'99 owners the P-38 is an option to set the end of the stroke. There are a few different heights available, the shortest was for the YZ with it's smaller flywheel. Bending the pronged leg was for the starting point which can add or reduce the total stroke.

Sudco also suggested putting a disc below the diaphram about 1mm thick to stop the stroke. A 1mm thickness would leave the stroke at about 2mm. This would work for any year.

A thicker disc would reduce stroke more.

I AM hoping, Taff!

what's a &%$#@!all?

"f****** worth nothing at all secondhand" can be abbreviated to &%$#@!all.


order the PAJ-SCREW & the 50 PJ.



Did you understand that bottoming the screw and spring does not measure the delay as I have described? Backing out the screw reduces the delay, which you must feel by rotating the linkage under the cover by hand and recheck as you adjust (not by turning the throttle either).

The setting on my 'WR was at about 3/4 turns. This was a used bike and the idle speed will have an affect on it. The measurement will decrease if the idle speed is turned up. There is no manual reference on this yet.


James, what is the factory setting on the screw you talk about? mine only went in 1/2 a turn before it bottomed out the spring.

I'm happy as a Titmouse in a Disney movie with my P-38. Factory R&D knew what they were doing. Yamaha followed their lead in '01.

[This message has been edited by Boit (edited 03-06-2001).]

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