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Throttle
Valve Emergency Repair
When you
change the needle position in the throttle valve by adding or
subtracting shims (or moving the clip on some needles), you must
remove a gray plastic plug to access the needle. Special care should
be taken when you replace the plug, because the four plastic
"fingers" that hold it into place are easily broken. Here
is a cross-section drawing of the valve (Yamaha part #5EL-14112-00-00)
with the rubber boot removed:
If one of
the fingers is accidentally broken off the plug will not be held
securely, and you'll have to order a new throttle valve. That creates
a couple of problems, 1)it costs about $35 and 2) Almost no dealer
stocks them, and Yamaha is often backordered.
If you've
only broken one finger off, all is not lost. You can make a repair
which should work almost as well as a new valve. Go to your local
hardware store and find a piece of brass tubing, 1/2" o.d. DO
NOT USE copper or steel tubing, as it will be too thick and heavy.
Create a small sleeve by cutting a 3/8" piece off the end:
Clean and
de-burr the sleeve. Using a small pair of needle-nose pliers, reach
into the valve and slip it over the remaining three fingers; it
should fit perfectly. The sleeve should not stand taller than the
tops of the fingers. Here is a cross-section drawing showing the
placement of the sleeve:
Here is a
close-up shot of the sleeve in place, also showing the location of
the missing finger:
Now you can
drop in the needle and shims. The gray plug and spring should snap
firmly into place and will be held securely by the brass sleeve and
the grooves in the remaining three fingers. The large diaphragm
spring will fit perfectly around the sleeve when you re-install the
valve into the carburetor body.
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