Broken throttle slide plates/ aka direct METAL injection

Please Help!

I have now reassembled my carb with the second slide plate but am unshure if I have put the accelerator actuating arm back on correctly as it does not seem to move much (about 3mm).

From the picture: does the spring and arm look like they are installed correctly.


As I cannot get my pic to appear. Could you please take a look at the following location:

Just had same problem on mine. The part is called the vacuum release plate. Im in Uk and Yamaha want to charge me £90 english pounds for replacement. Tryin to find a cheaper replacement elesewhere. After sales service is very poor in UK. Does anyone over there know how much a new one in the states is?

Here in Canada I think I paid somewhere around $170 for the slide plate and rubber seal.

I can't remember who it was on here but someone made one or bought a custom machined one. Throw out a new post about your carb slide plate and see what kind of response you get. Maybe contact TT store, maybe they can help.


I see that Ronnies store ( ) sells them for about $70 USD. This is the only place I have found them so far. Still waiting for a reply from manufacturers Sudco.

Had thought about the guy in Singapore who sells metal/aluminium ones but worry about what internal damage that could cause if it broke.

Anyone else got a price out there?

Well, it's happened again. I have broken slider number 3. This slider had about 2000 miles on it. I had the o-ring installed properly. I was doing wheelies and then chopping the throttle. This may be the weak link in the chain. This time, I got the pieces stuck in the cylinder. I had about a mile to get back to the trucks so I figured I'd just ride. About a minute later, the engine started making a LOUD rattling noise so I shut it off. When I went to start it later to let a mechanic friend of mine hear it, the motor was seized up.

Once I got it home, I verified the slider was cracked and took off the cylinder head. The piston and head were beat up and there was the remaining chunk of the slider sitting on top of the piston. Looks like the piece got jammed sticking straight up and would not let the piston go past TDC. Actually, the damage to the engine was purely cosmetic and basically took little bits of the surface carboning off the inside of the combustion chamber.

Now I have carb slider number 3 on order and am waiting for it to happen again. I will be much more careful from now on with my throttle chopping.

One major thing that has happened with my riding since the slider first broke back in '03 is that now I try to do wheelies as much as I can. Before that, I never really tried them. Since I have discovered how much fun they are, I do them all the time. Unfortunately, I don't have a smooth throttle hand and I end up chopping the throttle instead of rolling off smoothly when I am wheelieing. I think this has contributed more than any other factor.

I thought I remember seeing a post in the past that this may be caused by cutting your throttle stop to short. Don't remember for sure but you may want to measure it to be sure.

Rex, if that is true then it should only be happening to WRs with modified throttle stop screws. YZs should be unaffected. Has anyone with a YZ also experienced this problem? That would at least give us WR owners some piece of mind if the problem is related to cutting the screw too short and we chose to use a YZ replacement screw instead of cutting.

Anyone had this problem on a 01 or newer bike?

the 00' models onwards r running on the second genration of fcr far i've neva heard of people running this carb having dat problem..the design of the carb is different. the newer carb slide is position vertically straight whereas the 98-99' model carb slide is slanted at an angle...i suggest those wr running wif the first generation of fcr get n aftermarket slide or juz change to fcr2 or fcr3 carb..btw i cnc-machined my own throttle slide n been running them for almost 2 years wif out any problem.. stock slide plate is way too soft n brittle...juz my opinion :)

I just read a post from a dude with a 2000 model that has had a carb slider crack.

Are there aftermarket options available for this?

I bit the bullet last night and got a carb off of an '04 WR450 off of eBay. I paid $295 shipped to my door. I didn't want to do it because I have my carb dialed in so well. It has stock jetting but it has been deoctopussed and the accelerator pump is adjuted perfectly. But I am sick of worrying about the carb slider. Plus, this new carb will give me someting to do.

I'm planning on just taking the needle and all the jets out of the old carb and putting it in the new one. I have a feeling that the new carb's jetting will not work on my bike. Anyone know the answer to that question?

I think whats going on here is the carb body wears a bit where the slide sits and allows the slide more room to accellerate before striking the front of the carb and causing metal to fatigue. remember that when youre braking with the motor youre getting strong vacuum pulses through the intake trying to pull that slide forward. especially at high RPM..

Maybe the only way out of this is to have the thing machined and something inserted so the gap is what its supposed to be.

A really good test of this would be to check the gap in there occasionally over time with a small vernier and see if it grows.

Ive seen some carb designs where the slider rolls on wheels, maybe thats the way to go.

The slider carriage rolls on 4 wheels.

Not sure if the problem is eliminated yet.

Here is my 04 WR450 slide after about 3500miles. It hasn't broken but I am ordering a new one to put in soon, just in case.


Hey Luke

Check very carefully for cracks at the circular part of the stamped depression. Only one side of mine broke. The other side looked fine until I checked with a magnifying glass and a bright light. The side that hadn't snapped off was cracked around the entire circular depression. I wiggled it a bit and it opened right up.

Rex, if that is true then it should only be happening to WRs with modified throttle stop screws. YZs should be unaffected. Has anyone with a YZ also experienced this problem? That would at least give us WR owners some piece of mind if the problem is related to cutting the screw too short and we chose to use a YZ replacement screw instead of cutting.

I can't see how the stop could possibly be causing the plate to crack. The wear marks and breaks are at the bottom of the plate. When the throttle is closed the plate is trapped in a slot in the carb body while the slide itself is free to vibrate in it's shaft. I'd say the main reason that YZ's aren't breaking is that they don't do as much trailriding, low rpm lugging.

I have a 99, wr 400, bored out to 426, and have had the slide plate crack twice, I just called a Yamaha Rep and they say it's due to backfire, which seems to me a reasonable cause. Still i would like to have a steel or plastic plate that i would not have to worry about cracking, and alowing metal to enter the engine. Carb adjustments are not my stong point, and my bike does backfire once in a while. Not really something I would expect to harm the slide. But over time. The newer part has an "L" on it, where the older one has no marking on it.

My throttle plate just broke .....can I assume this problem has not gone away, and people are still getting broken plates ???

After breaking my throttle plate twice I decided to have my own plates made through a performance parts machining outfit. The new style plate that is in my 98 WR 400 has lasted a year without a problem. I had a few extra made and I am willing to sell them to anyone wanting a better part in there bike. I am tired of those stock plates going through my engine. One actually made it into my muffler. It is all balled up from the heat. My bike does not back fire either, and is completely stock, and still broken plates, except for my new one.

thanks for the offer ....I am looking into having some plates made here in the UK .....

these carbs are used on lots of bikes ....there must soon be loads of them coming up for a breakage :thumbsup:

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