One unfortunate day my Yamaha WR400F would not stop revving high.
I had a hard time figuring out the problem and finding a replacement part for my Yamaha WR400F 1998, I’m hoping this post will help some people out that are having similar problems.
WR400F carbonator fix
Long story short the problem was in the carbonator, with the mechanical help from my dad, we took the bike apart.
Keep in mind that neither of us are mechanics, this post more of a pointer in the right direction.
After taking the bike apart and getting the broken throttle plate out, I spent sometime researching.
Turns out there are a lot of people having the same problem with stock part. I found a guy from America who had improved versions machined.
Luckily the piece got stuck just before entering the engine. In the worst case the piece could reck the whole engine, but I have also heard of others, having smaller pieces running through the engine and out the exhaust.
Keihin FCR “L” vacuum release plate / throttle plate replacement
“These are updated versions that won’t break like the stock units. They are many times stronger and hard clear anodized for a long service life. I designed these parts and had them CNC machined out of billet 6061 T6 aluminum. The stock units tend to break and the pieces run through the engine, sometimes bending expensive valves. I had 2 of the stock units break while in my 1998 Yamaha wr400f dirt bike. The stock units are junk, no matter how many times they claim to have superseded the number. Luckily my engine passed the pieces through. I actually found a corner of the stock plate in my muffler.” – kmb321
Here is a link to his ebay where you can find the Keihin FCR “L” vacuum release plate / throttle plate
(New on the left, old on the right)
REMEMBER to swap over the rubber ring seal from the old plate to the new, and keep note of which side is facing up, as it has a grove on one side.
The new improved throttle seemed to be much strong than the stock plate which I was able to tear the other corner off. We put the bike back together and gave it a service and a clean, and it runs better than when I brought it!