Clacking, stuttering, and sputtering - oh my!

My 2008 wr250x clacks and stutters under heavy acceleration. I've found a couple of other threads describing similar issues, but they end with the problems going away as the bike warms up. My bike clacks and stutters consistently, even after being ridden around for a while with a just-filled tank. When I baby the throttle it usually doesn't clack or sputter. I recorded a video of the sounds to see if anyone here has any troubleshooting suggestions.



The clack doesn't seem that loud in the video, but I can feel it through the frame/seat when it happens. It sounds like it's coming from the back of the bike. The stuttering can get pretty severe - you can see in parts of the video that the front bounces as the forks compress/decompress with the stuttering.

Backstory:
I bought the bike about 6 weeks ago from a dealer. This particular bike had been damaged during shipping and sat around some Yamaha shops in western Canada until a local dealer bought it and fixed it up for sale. The plastics at the front have some pressure marks (slightly lighter than the surrounding blue), which fits with how the dealer described the shipping damage - the crate the bike was in was squashed. The dealer replaced the headlight and front signals and took off some stickers that had been scratched up before putting it up for sale. It had less than 20 k on the odometer when I bought it. So even though it's a low k bike, it has been sitting around for a few years before I bought it.

I've checked the chain tension - there's about 35mm play, but that's not on a proper stand since I don't have one handy in my parking garage. (The shop manual says it should be between 40 - 45mm or something like that - I figure with both wheels on the ground the slack should be a little less than the service manual spec.)

From the other threads I've read, here's the list of possible causes:
- bad fuel pump: the stuttering doesn't match up with the descriptions of bad pump issues, and as far as I can tell the pump isn't making any funny noises.

- chain slipping: the clacking sounds could be that, but I'm not sure I know what chain slippage actually feels like. The sputtering and stuttering doesn't have a harsh attack... it seems more like it's a fuel delivery issue? Assuming the chain is the original four year old chain, maybe the lube from the factory has gummed it up or something as it sat before being sold?

- bad gas: I've filled the tank twice with premium since I noticed the issue, so I assume that would have flushed out any bad gas if that was a cause.

- loose front sprocket nut? I have no idea how to troubleshoot this one further.

- accelerating too hard: I'm a bigger guy (275 lbs without gear) - maybe I'm "too big" for the bike? I've seen pics of other riders at least my size, though... and none of them have reported similar issues.

- I'm clutching out "wrong": possible, but I'd have no way of knowing otherwise. Feel free to critique that if it's obvious from the video.

- an aftermarket fuel programmer / exhaust pipe / magic farkle will fix it: I do intend to mod the bike after I'm done breaking it in, but I refuse to believe these issues are just part of how the bike performs unmodified.

The bike is currently at 350km on the odo, and I've been very aware of these issues ever since I tried some wheelies after some light dirt riding about a month ago. The bike was so new, though, that I may have been babying it or ignoring the issues if they were present before that. The dealer test rode it before I picked it up and they seemed to think it was good to go.

While I consider myself a pretty responsible rider, I bought this bike to hoon around on in my own way, and it bums me out that I can't flog the bike. It's also a bit scary when I try to pass and the bike starts stuttering and bouncing at high speed! If I can't pin down some leads on this I'll take it in to the dealer - I've got until the end of the month on a power-train warranty.

Oh great and wise wrr/x folk - I appeal to your knowledge and compassion!

yeah - not a good sound.

You bought from dealer?

Take it back to dealer.

It's not you being too hard on throttle or clutching wrong. It's not you being too big for bike.


A few things you can try, or I would try.

See if you can get a friend in a car to video you in a parking lot doing same acceleration drill.
Have friend video the chain and swingarm area specifically.

Some of the "clacking" might be chain slap on swing arm.

You don't need a special stand to check chain tension. You can do it on side stand.
Push up on chain under swingarm about half way between axle and swingarm pivot.
Chain should come to within about a half-inch of touching underside of swingarm.

A "loose front sprocket" is easy to check. There's a plastic cover with three bolts you can remove to get to front sprocket.
Place your left foot on footpeg. The cover is by your left ankle. Countershaft sprocket is behind that cover.
remove that cover before you do the video (if you can do video).

Check to see if any teeth are missing on rear sprocket. Or if teeth on rear sprocket are starting to look worn or bent around the points.
(to see if chain might be jumping teeth)

Can you look and see if your bike has the "chain slider" or "swingarm protector" piece on it? The very front edge of the swingarm should have a black plastic piece covering both sides to protect swingarm from chain clap. Should be easy to see without touching bike with a wrench or any tool at all.
Again, look at swingarm by area around where your left footpeg is (but behind frame rail).


Since bike was damaged before you purchased it there's no telling what could be going on.


Is bike 100% stock? Stock exhaust? Stock airbox?

I would take back to dealer immediately, and show them that video too.

I tend to think it's a final drive (chain/sprockets), or even a clutch issue. I'd have that thing back at the dealer if it's still under warranty.

The clacking sounds exactly like the chain skipping sprocket teeth.
My guess is the chain has some kinked links that won't straighten out and/or it's simply too loose.
(Just don't overtighten it, either.)

Since it was sitting for years, has anybody inspected the airbox inlet and the innards of the airbox and the air filter, itself, for rodent infestation?
In fact, the entire bike (wire insulation, for example) for rodent munching.

Back to where you bought it from for repairs.

Whatever it ends up being, be sure to come back on here and explain the mystery.

Adjust the chain so that when you push up on the lower side in line with the mudflap (about mid chain) there is about 1/2" or 13mm between the edge of the chain and the bottom of your swing arm. This is done ON THE SIDE STAND per the owners manual.

I think you are setting it too loose but I also think you have frozen links. Check the front of your swing arm (bottom side) I bet it's chewed up pretty good as a result.

Man that sucks. Was not expecting to hear AND see that in the video. Do the tires spin freely? Can you put the bike up on a stand or 5 gallon bucket and spin both front and back tire? Sounds and looks like to me that something is binding. How do the brakes feel?

Could also be a loose chain and some missing teeth on the front sprocket given the miles... I had 3 missing teeth on the front when I changed sprockets/chain around 12K miles.

My guess...
The 08s had the rear sprocket with the rubber coating, this combined with an old stiff/kinked chain will cause the chain the skip.
The bike may have next to no miles on it but the chain will rust and get kinked links sitting around.
Have a look at the chain, kinked links should be easy to see and if the links are stiff and stay bent when you bend them by hand its toast.

Derp derp derp... well, this is embarrassing.

So I adjusted the chain as per Arkmage's suggestion and both the clacking and the sputter have cleared right up. Here are some pics of the before and after:





I looked over my (Canadian) owner's manual, and it says the slack should be 1.38 to 1.77 inches with the bike on the side stand... which is similar to what the service manual says it should be with the bike on a service stand?! Arkmage's procedure and measurement makes much more sense to me... but I wonder why Yamaha would give such a different value? Maybe I'm not measuring the slack correctly according to Yamaha's procedure...

Although it seems tight to me (my other bike is an F800GS which has a notoriously loose slack spec), it worked. I also check the swing ar guards (above and below) and although there's a bit of plastic eaten on the bottom guard, I can't find any sign of actual swing arm being chewed up. *sigh* Sorry for getting all of you involved in such a simple issue!

Here's a quick vid of how it accelerates now, just for kicks:



Thanks again for all of your input! I'll try to make it up with a really interesting mod thread once I start modding the bike.

PS - The tool kit included with the bike is hella sweet. My beemer came with a useless screwdriver thing and a plastic shock adjuster paddle that must of cost BMW about $0.25 total.

PPS - I'm pretty sure the bit of sputtering in the video is me hitting the limiter.

yup... that's the limiter.

I couldn't find the picture, but the method I described is what Yamaha revised the procedure too in the 09+ manuals. They realized after '08 that they screwed up.

Sweet! Don't ya just love when it's a simple fix?

For revised chain adjustment: click me - see jager's post first page

I do mine a different way, but comes out pretty much the same. Where the black guard ends on the top of the swing arm, I insert 3 fingers on top of it.. The chain should not cause any pain on your fingers, just snug. Easy way to check chain when stopped. You might need to check the other way if you have very small fingers or very large just to see where you are..
ymmv../