Question on AP tuning for 07 450 XC-W

Hey all ... quick question for you.

My riding buddy has a 2007 450XC-W (RFS) that STILL has a slight BOG or delay when cranking the gas (aftermarket slip on .. non restrictive). It has also been know to backfire a bit when revved up and down (in neutral). It has a JD jetting kit installed and the AP mod done (using o-ring)

I have tried every jetting combo, fuel screw adjustment, etc. ... so these can be ruled out.

Here is what I am thinking might be the culprit (based on a DRZ400 I used to own with the same carb).

I was going to try ADVANCING the AP timing by turning in the AP screw about 1/2 a turn and wiring the AP linkage together. Sound logical ???

Has anybody else done this ??? Is this fairly common for this model bike??

The thinking behind this is that the AP pump is "lagging" a bit behind when the throttle (carb slides opening) is being twisted.

Any input would be appreciated :smirk:

How to eliminate the 'Bog'

You are on the right track. Fuel screw is for idle only. Needle, main is for steady throttle. None is dealing with accelerating.

Confirm he has a good squirt BEFORE you mess with anything. The oring, if it is in good shape, should be fine. JD often gave two, a thina dna thick. The thick one should of been used or both, not just the thin one.

Yeah I have the thick o-ring installed, so that is why I am focusing on the AP timing screw.

Anybody adjusted the screw before ?? I am going to go in 1/2 turn and check to see if the "delay" is gone.

Thanks

How to eliminate the 'Bog'

You are on the right track. Fuel screw is for idle only. Needle, main is for steady throttle. None is dealing with accelerating.

Confirm he has a good squirt BEFORE you mess with anything. The oring, if it is in good shape, should be fine. JD often gave two, a thina dna thick. The thick one should of been used or both, not just the thin one.

PS .. just noticed that you "linked" to another post.:smirk:

WOW ... maybe the BEST write up I have ever seen on tuning the FCR Carb ... and I see you are the author.

Well done :smirk:

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