WR400F / YZ400F (need tech info on carb differences)

[Terry Burke]

Finally got to ride my new WR, but not before a frustrating day at the shop.
The WR has extra plumbing on the left side of the carb, from what I can
figure out it has something to do with the pilot air system, but thats all I
know. The bike when warm would flat out die if the throttle was cracked
wide open from a idle. I know that is commom with some four strokes but
having tried the same thing on the YZ400F only produced instant RPM's. I
tried removing the device altogether and sealing the pilot air jet #2 and
the vacuum port, but there was no improvement and the idle became very rough
or lumpy. Comparing specs on the two models both use #45 Pilot jet but the
WR uses a #DTM Jet needle and the YZ uses a #DVR Jet needle, also the WR
uses a #168 main and the YZ a #175. The differences in the main size I
think is relative to the difference in the taper of the Jet needle. I would
really like to remove this vacuum device because it hangs out in the open
and is a prime candidate to be riped of in the first tight bush section. If
anyone has insider knowledge of the workings and purpose of this stuff I
would appreciate their insight and assistance. Feel free to E-mail me or
reply to this post.
P.S. having owned a KLX650 I can safely say that this 400 truly rips.
Terry Burke
ts_com...@bc.sympatico.ca

[ROB HUNTER]

I've had problems with the adjuster screw & locknut that connects the
throttle shaft to the slide lifting arm. At first it was loose (from the
factory) this resulted in the bike idling too fast on minute, then
coughing and stalling the next. I foolhardly just nipped this up and
started the bike again. Now it wouldn't idle at all, and appeared though
it had a #65 pilot jet in the carb, also it backfired when the throttle
was closed from mid throttle.. After some messing around we set the
screw tight with the throttle shaft in the idle position with the slide
just bottomed in the carb. The bike now runs correctly.

The problem is the TPS is very sensitive to change and this cocked up
the timing in the ecu.

Rob H (NZ)

[Terry Burke]

Rob, you didn't say what model you have. I'll check the TPS settings. On
the idle I also found that even with the idle screwed all the way in, idle
is barely hight enough. changing the pilot setting from 1 3/8
to 1 5/8 seemed to help responce a little but did not raise idle RPM. This
was done at 1200 ft elev. Have any thoughts on a pipe yet, I'm trying to
get some info from Dirt Squirt today.

[ROB HUNTER]

I was refering to the YZ400F. The trick is to make sure the slide is
bottomed with the idle screw backed right off before you set the
throttle shaft, with the TPS hopefully in the right place. Also check
the idle mixture once you have the bike running. This then gives you
enough range of adjusment to set the idle speed. Your problem sounds
very similar to the one we had. The Yamaha book is very vague about
setting up this carb.

See http://www.lifenet.com/brm/fcr-jetting.htm
Although this is a road race site these guys have been tuning these
carbs for years, so they may be of assistance.

Rob Hunter (NZ)