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Broken choke flap

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The Choke flap on my xr400 broke a few weeks and ago, which eventually led me to this forum. After searching and reading old posts it seems some people don't think this can happen even when warned, or think its the screws that come off. For me the bottom of the choke plate broke off after the flap beat it off and that approx. 3/8x1-1/2" piece made its way into the combustion chamber and luckily only closed the gap on the plug, since I didn't know about the choke flap problem at the time I thought the timing chain must have slipped and was quite surprised when I found that piece of the choke flap sitting on the piston and had to try and figure out where it came from. I am still amazed that big piece managed to get through one of the intake valves and into the combustion chamber with no damage to the engine, not even a bent valve! There was a warning about 5 minutes before that happened and that was that the throttle got stuck at about 1/4 throttle for a second. This is a '99 my brother got in '02 so it does have a bit of time on it, but if you haven't yet, at least silicone/rtv your choke plate or get an aftermarket one.

I have pictures if anyone wants to host them or see them.

Joel

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This is old news, the old "broken choke butterfly" was a reasonably common on high milage XR600's and has happened on the odd XR4. It happened to one of my XR6's and unfortunately did a little more damage than a closed up plug gap, it put a deep score in the cylinder that rendered it useless as it was the nickelsil coated cylinder model (1988-90). As a precaution ever since, I've been removing these choke plates and replacing them with an aftermarket type bought from Ballards Xr's only in OZ, these have no flap which eliminates any weak point from the plate!

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I bought my bike used and the first thing I did was to replace the flap with one from XR's Only. Man am I glad I did as the stock flap was cracked almost halfway through.

Cheap and easy to install and will save you some big money if it were to fail.

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I know its old news, but I wanted to make sure everyone knew that it can and will happen if you don't do something about it. I would post the pics but I don't have anywhere to host them.

hxr400:

I was going to e-mail you the pics but this forum doesn't seem to have the e-mail through the forum feature....or at least I didn't find it yet.

Joel

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The real maytery is what causes it to happen. With a used bike, you have no idea if the previous owner had brain fade and rode around all day with the choke on the 1st notch. (I'm guessing that something like that may be the thing that does it in...)

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You can host your Photos at: http://www.bikepics.com/

Then link them to this forum.

I have also changed my choke plate. I got a Precision Concepts Billet choke plate. I change it as soon as I found out they break.

But I think its more common on the XR600's.

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The real maytery (mystery) is what causes it to happen.

A good explanation of how it comes loose can be found here.

I would not recommend trying the temp repair shown, just replace the stocker with the aftermarket choke plate (I went with XR's Only).

And use the newest #2 phillips screwdriver you have (or a fresh apex tip) to get the stock screws loose... :cry:

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Some of the guys were making their own out of old 2smoke reeds, the carbon/graphite ones, so if they broke, they were "digestable". I've never owned a 2, but am looking around for somebody with some old reeds to try. :cry:

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old 2smoke reeds, the carbon/graphite ones, so if they broke, they were "digestable".

Digestable :cry: We use air filters to keep ultra fine dust out because it damages engines, but you want to run the risk of lunching some carbon/graphite!!! :cry:

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Well I was all set to upload the pics to bikepics, but I decided not too when I read this:

"Due to increasing traffic I am now deleting all non bike photos that are uploaded. If you upload a photo that does not have a bike in it then it will be deleted within 24 hrs. This also includes forum avatars and other pictures that are uploaded solely for forum posts to link to."

I cropped them down to 280k total, so it wouldn't be much traffic but I rather not annoy the guy.

I got a new plate from XRs only and its way nicer than that crappy pic on their website. Oh well, its a good excuse to rebuild the top end. While I'm waiting on gaskets and such to come in, I'm rebuilding a semi-basket case xr500 and I noticed the carb is almost exactly the same design as the 400 except it has an accelerater pump which is made into the bowl, so it seems like it would be easy to make it fit the 400's carb, all you need is to drill a hole into the throat and put a nozzle, but back on topic, it has a solid choke plate. If the 500 didn't need a backfire flap, why would the 400?

Joel

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Not digestable on purpose, but if something does go through the engine, I would rather it be a carbon fiber than alum. or steel. The carbon fiber reeds were designed to go through a 2 stroke with less damage.

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Nice pics fishbone, after reading most of the post on this topic I took it as the Flap was the problem, now from the pics I see the bottom of the plate is also a weak point. How was it replacing the plate, did you have any issues removing the mounting screws? I've been reading that they are crushed on the one side so they dont fall out.

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I had no problems at all. They came right out. Luckily my son was smart enough to not pull start the bike when it wouldn't start. I guess the damage could have been worse if he had.

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Mine looked just like that but the piece that came off was still in one piece and far less chewed up looking. I say was in one piece because when I handed it to my dad for him to examine, he broke it to see how strong it was. The flap on mine also has marks and is bent from beating on the screws.

I took my brothers '02 apart to replace the plate and its different from the '99. It is made out of a solid stamped plate instead of that weak cast junk, but it still has the flap.

I didn't have any trouble getting the old screws out, but I messed up that spring on the end of the shaft and it took forever to get it to not lock up, don't think I did anything different but it just happened to work that last time I put it together.

Joel

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