2004, WR450f backfires & sputters

Hi I'm new here, this place seems awesome and lots of activity....... Joined a couple supermoto forums and haven't had much luck.

Anyways here's my issue, I bought this bike as an off road, but I've now got it street legal'd as a Supermoto. When on highway holding throttle at a steady speed the motor gives a tiny cough or sputter. It also backfires on down shifts (which doesn't bug me too much). Last thing is the black residue on the end of my pipe and on signal light and fender. The bike is now fully piped (pro circuit Ti-4) but had the sputter with factory pipe. The guy I got it from says it has factory jets which is what pro circuit told me I need to run this Ti-4 system.

Any input would be great

Thx in advance

" Factory Jets" ?  You mean stock jetting?


That's no good.


You have a lean condition stock, and adding the pipe makes it way worse.



You need to determine exactly what jetting you have, and read the FAQ section at the top of the forum on how to properly jet the bike.


I would read all the FAQ's then come back and post with questions.


There is so much to cover, and we have no idea what you know, or what you are able to handle.

Yes it's stock jets, and pro circuit says that's what I'm to run..., I thought that was odd 4sure

Which procircuit pipe

This is what you should be runnning according to procircuit, and these are not stock jet specs'




NFNT  ( I'd use a NCVS)
fixed / 4 th clip


Edited by Kah Ran Nee

I have a mate with a similar issue with his WR at constant throttle. I really don't know too much about it or why it does it but the Throttle Position Sensor  is the cause of his issue. He generally disconnects his for road riding and puts it back on for the trails. I am not sure that this is the best approach but it may be worth disconnecting yours and going for a ride to see if it helps to fix the problem or at least rule it out.

The head pipe/silencer is a Ti-4.

Here is a pic of my email reply from pro circuit ImageUploadedByThumper Talk1405331492.260099.jpg

That might explain all the black crap all over end of pipe and fender

That might explain all the black crap all over end of pipe and fender

Yup. Thats putting a heck of a lot of fuel when starting and going to mid throttle. I would bet its a pain to start when hot. Typical fuel screws are between 1 1/2 and 2 1/2 depending upon elevation and temp.

If you get above or below those settings you need to drop or get a bigger pilot jet.

If your at lower elevation you could go to a 48 pilot and 2 turns. I would t change the pilot anything above 3500ft.

I ride between 4k and 9k. I found better performance at the 3rd clip on the needle. Everything I know is because of the man that has responded above Mr. K.

Your lucky the fuel screw hasn't fallen out at 4 turns.

Edited by RMK800

You pretty much have to take charge of the carb yourself

Do a full rebuild, upgrade, and re-jet

They come 'unfinished' from the factory.


The FCR carb is essentially the same for all pre 2009 dirt bikes.....






Unfortunately, the ignition system that comes on all pre 2012 WR's is defective from the factory; it exhibits a 'toggling / stutter' at constant throttle. Unplugging the TPS from the harness fixes it. 

Keep this in mind.

Guys I appreciate all your knowledge cause most of my experience is with 2-strokes. This TPS, I gotta get this baby unhooked but I gotta ask ..... Where is it?

The bike actually starts mint hot or cold, don't even need hot start.

I read in a thread from you Mr. K, that the fuel screw is anodized red....am I correct on this? Here is a couple pics of pipe and of fender and little guard infront of rear signal (prevent melting it again lol) the guard was plan aluminum...... Hard to tell

ImageUploadedByThumper Talk1405379665.792222.jpgImageUploadedByThumper Talk1405379698.062624.jpg

Other thing is that it has no bad spot at all, low/mid/high..... Throttle response is awesome and lots of power

NO WAY!!!! I will forsure. Thx again

TPS unhooked, '03 manual downloaded!!!! (Close enough)

Just got back from a 15 min test and it only had a couple teany tiny coughs when held throttle steady. Now just to get the black soot from coming out of the pipe

Good news about the TPS helping the problem.


How quickly does the black soot build up? and is the exhaust visably sooty as it comes out from the muffler?


One of my old bikes used to have this build up even though it was running very clean (spark plug was a nice chocolate brown all the time), I found that by shifting the number plate so that it was no longer catching any of the escaping exhaust I no longer had the sooty build up.


Does your number plate get hit by the exhaust gas?

It builds up almost instantly, the number plate doesn't really affect exhaust flow I don't think. Here's a picImageUploadedByThumper Talk1405418140.533697.jpgImageUploadedByThumper Talk1405418192.202214.jpg

Edited by ONTHEPIPE33

Looks like the indicator might be in the way a bit? That wouldn't help the issue but it seems like there is more to it. Mine was a slow build up over time. Jetting could well be the problem and i am certainly no expert on that.

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