Hey guys just picked up my '01 426 and took it for its first ride. As I expected, it preforms really well the only thing I have noticed is that there is a slight delay in throttle response at low revs. Its not really noticeably enough to effect the performance but I was just wondering if anyone knew what this might be or how I could get rid of it. The bike is completely stock so the exhaust hasn't been changed or anything.

Sorry if this is a simple topic that has been covered before but I have only recently joined and havent had a bike for years so I'm a little rusty on the details.


also I know this has been covered in another forum but the bike is leaking oil from the breather tube. One guy said this is normal but it seems to leak a fair bit. When I park the bike there is oil sprayed around the rim from when I was riding. Should it be leaking this much?

It should drip one to three drips after parking it, if it spews a lot while riding, it could well be that it's over full, many don't know the proper way to check the oil level in these bikes since there's a bit of a trick to it.

Read the manual on how to check your oil, do an oil change according to the manual, also, if you need the manual, there's a link in the stickies up top to Yamaha of Australia where you can download the whole shop manual for free.

Soco- Good choice, you are going to love that bike. I picked mine up new in '01 and still love it. Don't worry too much about the oil leaking from the breather hose, the yzs do the same thing. I followed the manual exactly to make sure I didn't overfill and it still does it so don't sweat it.

As far as the delayed response, you may want to try a quiet after market pipe eventually. The stock is really heavy anyway and completely corked. This is a must-make sure the throttle stop is taken out-you just limit your power if you don't. I did the gray wire modification and I didn't notice a significant difference even though everyone swears by it. Also, I recently replaced my chain and sprockets and the dealer accidentally gave me a smaller sprocket that was one tooth smaller. I think stock is 12 and he have me an 11 or maybe its 13 to 12. Anyway, it was the best mistake since I have great low end torque which is perfect for hill climbs. I rarely poop out during slow speeds. You will give up top end speed but who cares!

Hope that answers your questions. Have fun on that bike.

thanks for your help. As far as Im aware australian spec wr's dont come with the gray wire or throttle stop so that shouldnt be a problem. Ive been flicking through the manual I might consider adjusting the jetting to smooth the throttle response a little and I was already thinking of fitting an aftermarket pipe once I get a few dollars together so Ill ride it for a little while longer then have a look at it.

cheers guys

Definitely get an aftermarket pipe.

I was lucky enough to buy my bike second hand with an aftermarket pipe already installed.

It wasn't until I put the stocker back on to get a roadworthy that i realised how restrictive the stock muffler is. If you think it goes well now, wait until you get it breathing properly. It's a different bike.

sweet well im looking at a second hand e-series white brothers exhaust at the moment so hopefully that will make a difference

Soco - the bog is what most 4 strokes experience, it's a delay that's supposed to be fixed/helped through the AP (accelerator Pump), however, still ocurrs some times.

You can get a Boyesen AP cover (aftermarket) that supposedly really improves it, or if you're daring, start messing around with the AP itself and adjusting the timing and duration of the squirt which is also supposed to help eliminate it.


I should be getting my White brothers e series next week (also gently used) but won't get to try it until spring.

The above thread reference is a good read. with good explanations of the FCR carburetor and how it functions.

Things to be careful of:

Your carb does not have a leak jet so don't make yourself crazy thinking about it.

The BK mod applies to your year carb. it worked very well on mine. Don't spend a lot of time trying to get your squirt below 1/2 second. 1/2 second is just fine for practical use. http://www.thumperfaq.com/ap_mods.htm#BK

when you have your carb running well set your TPS voltage to the high end of the service limit as described in your manual.

If you want to go crazy reading about tuning your carb and the earlier FCR carb(WR400) search threads by Taffy

Good Luck let us know how it turns out.:cool:

thanks guys. As i mentioned at the top of the thread Im still a bit rusty in the mechanics department so I dont think ill start playing with the carby til I do a bit more reading up so Im considering an aftermarket AP cover. Do u know how much the boyesen will set me back?

I have heard mixed reviews on the AP covers in general, not just the Boyesen ones. However, I would say that the majority of them have been negative reviews. No problems with functionality, but they don't get rid of the bog you are experiencing. Check into the BK mod and the AP Wiring mod, I think you will find it if you look through threads by Redbeard. He kind of pioneered this modification. I would be running it if I had not already done the BK mod, I think it works a little better. Just my 2c, take it for what it is worth and I hope this helps.


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now