simple jetting help

I have the Australian , Canadian wr400-99 which was running great untill I started tinkering with it.

Now I have two problem spots with my jetting.

I,ve spent big $$$ on jets & neddles & now I must ask for help. PLEASE PLEASE PLEASE.

I opened up the hole in the end of the muffler from 3/4 inch to 1 1/2 inchs.

Now I have a stumble when I snap the throttle open from the closed position.

I also have a flat spot at half throttle.

I ride at less than 1000ft.

My current settings are,

DRM#3 160main jet,200main air jet,#45pilot jet,#75 pilot air jet,#62starter jet, 1 1/4 turns pilot screw, wr timed, air box lid off,

PLEASE PLEASE PLEASE I don't want to pull the carby apart again.

I'm mostly after strong mid range & bottem end for single line trails & snotty hills.

do the Taff mod to your APJ and go down to a 42PJ. that will cure the bottom end. as for the mid top would you describe it more clearly please?



I'm not up to date with the Taff mod to the APJ. Could you explain this please.

As for the mid top flat spot, it has a dull performance spot of about 3 seconds long at approx half throttle, but only in the mid rev range -one gear too high accelerating out of a corner or climbing a moderate hill when you don't want a lot of revs.

For that approx 3 seconds of dull - lagging performance the main sound I can hear is the air cleaner sucking air with little or no acceleration.

Once the motor gets through this spot it accelerates hard & fast again.

It only has the dull spot in the mid rev range at half throttle, If I was one gear lower & the motor was reving faster but still at half throttle it would run fine.

I hope you can help.


Also could you explain the effects of changeing the pilot air jet size & the main air jet size.

Does increaseing the number make it richer or leaner.?

I'm used to two stroke carbys which don't have these.

Thanks for your priceless help.

Know body in Australia has any idear about carby setups on these bikes.

What clip position is your needle jet in? I just had a similar problem with one of my bikes after some mods. You may need to drop the needle.


I've tried clip positions 2 & 3 from the top.

Position 3 gave me slightly more power in the mid range than position 2.

But the dull spot at half throttle never changed at all. It was the same with both clip positions.

So now I've left the clip in the DRM needle in position 3.

Any suggestions ?

go to clip 1 on that needle. that will be making it leaner which is what i think it needs. are you running an open pipe?

maybe the home made exhaust isn't helping things. anyway drop the needle and put taff mod in the search. also go back 30 days and find the bottom of "jetting Qs". it was used only about 11 days ago. for pictures there is a "Taff Mod" in the suzuki section that has pictures.


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