99 WR 400 AIR CUT VALVE?????'S
Tangi8u
??? ON A 99 WR 400
What is the purpose of the " Air Cut Valve"
There is no air cut valve on a YZ.
One end of this valve goes to vacuum side of the carburetor.
The other side is on the inlet side of carburetor.
Has any one removed this valve?
Reason that I am interested-
Ever since I got this bike 300 miles ago, I have been fighting the same
problem.
When one starts the bike cold, it will start on the 2nd kick every time, but if
you take off and the bike stalls on power. Restarts " SUCK"
The bike runs like it is way lean for around ten minutes, popping and
hesitation. After that it ripps.
I have turned my pilot out 2 ½ turns.
I have tried choking no choke, hot air valve out air valve in.
The best way that I have found to restart the bike is to open the compression
release handle and kick thou around 10 times and the start the starting
procedure all over.
Choke TDC 19 Degrees past and kick.
When I go out for a play ride and have the time to let the bike warm up, isle
for about 2 minutes, it seem better.
But when I am at a race (ISDE'S or SCRAMBLES) I am not granted this luxury.
It has cost me minutes………….
I have talked to two other WR owners. One runs in my same class " Open Expert",
and he said that he is fighting the same problem. The other guy running open
amature, and says that he has not really noticed any problem except for the
popping,
I have two other buddies with YZ'S and all one has to do is start the bike,
drop the hammer, and the front end the air.
Thanks for any insight on this Problem
Tang
Mike Hobbs
>When one starts the bike cold, it will start on the 2nd kick every time,
but if
>you take off and the bike stalls on power.
Does it quit as you crack the throttle or at full throttle? My WR will die
once in a great while when the throttle is cracked. I'm going to try a 48
pilot jet and see if this helps.
Mike Hobbs
Jay C
>
>What is the purpose of the " Air Cut Valve"
Wild guess, but that is probably an anti backfire valve that keeps the bike
from "popping" from the exhaust (as the YZ4 is famous for) when you cut the
throttle at high RPMs.
Jay
Drehwurm
>What is the purpose of the " Air Cut Valve"
> ...
>When one starts the bike cold, it will start on the 2nd kick every time, but if
>you take off and the bike stalls on power. Restarts " SUCK"
Before attempting to fiddle with the jetting you should make sure
everything is working fine - like there is no dirt in the carb, the
acc. pump is working, ...
With the FCR carbs the idle/slightly above idle mixture is not only
controlled by the pilot jet, but also by the "slow air jet". While the
YZ has an no. 100 slow air jet, the WR has a no. 75 plus an additional
air jet which is opened and closed by your "Air Cut Valve". Under
normal working conditions both jets are open, equaling the no. 100 jet
of the YZ. But when a high vacuum condition is created (like closing
the throttle at high rpm) the " Air Cut Valve" closes the additional
air jet causing a RICHER mixture. Now this gives you a really easy way
to check if your problems are created by a lean idle mixture. Just
plug the hose (the small one going to the carb body) of the additional
air jet and you will have the same effect like going to a richer pilot
jet. Many people who just removed this "anti-popping-device" without
changing the slow air jet never though about this and their bikes are
still running great. It should be obvious now, that the stock jetting
of the WR is too lean (especially for cold weather and/or open
exhausts).
What are your options now:
1) Just remove the "air cut valve". This will give you a slightly rich
idle mixture without any ill effects and should cure your problems
(remember, you can try this first without removing anything; just plug
one hose)
2) Remove the "air cut valve" and go with the no. 100 YZ slow air jet
and a no. 48 pilot jet. It is more work, but should give you a near
perfect idle mixture.
3) Leave the "air cut valve" as it is and go with a 48 pilot jet.
Haven't tried this, but should also help.
This is just from my personal experience and there is no guarantee
that it will work with your bike and situation.
Michael
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* mpe...@ibm.net
*
* 98 Yamaha WR400
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