australian 03 wr 450 backfiring on decel

8 replies to this topic
  • thumpawoody

Posted August 27, 2005 - 04:04 AM


hi guys ,
i know that this subject has been covered to some extent and I have searched and read postings about similar problems.
after checking for all of the obvious faults
1. lean idle mixture.
when i pull on the hotstart with the bike idling the revs increase and infact i have to use the hot start to start the bike once it is warm 90% of the time, so im convinced the idle mix is tending to the rich side.
2. loose exhaust fittings .
I replaced the muffler - header pipe gasket as it looked sus and i got some improvement.
I still loudly backfire on heavy decel
I am running the standard 03 aus muffler (has only 20mm outlet)
i do not want to change muffler, the bike makes enough power for me and noise is becoming a problem where i ride
any suggestions would be great


  • bdmmotard

Posted August 27, 2005 - 08:28 PM


in the thread "going fcr1 to fcr2" there's a lot of info. i had the same problem but it turned out to be a loose header fitting. Have you seen if your pipe needs repacking?

  • flatnacker

Posted August 28, 2005 - 05:03 PM


Im having the exact sam e problem...its like riding with a freaking shoit gun going off every couple of mins!!!

  • gregwr450f

Posted August 28, 2005 - 10:58 PM


I have spoken to a mechenic about this "problem" he reckons it's completely normal under heavy de-cell, it's just a bit of excess fuel burning off, I think you will find the Gas Gas 450 will never back-fire due to it's fuel injection.

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  • 450high

Posted August 29, 2005 - 01:41 AM


I rejetted and the backfirring is gone.Also have better bottom end.You try turning out the idle jet 1 full turn.

  • Indy_WR450

Posted August 29, 2005 - 04:29 AM


Try an 04 needle in clip #4 and a 48 pilot jet. :D

  • Matty05

Posted August 29, 2005 - 07:11 PM


Make sure you have that header in exactly perfect.

My bike was so bad it was spitting blue flames about a foot out of the Procircuit with
the spark arrester in place. I got a mate to help me line it up properly and it has
stopped the back firing and changing the jetting actually does something!!!!!. It still has a bit of a bad popping when the throttle is closed so I think the gasket is still suss.

Put a 48 pilot in it and set your fuel screw. I can start my bike first touch of the button (or first kick for something different).

  • cruise

Posted September 04, 2005 - 04:02 AM


I think u will find its the cooller weather making your bike run leaner rejet it i did my bike dont back fire but then again it will start to warm up soon :D :D

  • 450high

Posted September 08, 2005 - 01:47 AM


I had the same problem until i rejetted.Get the jet specks of indy as there spot on.Theres a bloke down gipsland way that goes by the name M.C EXHAUSTS he can mod your original muffler so it goes alot better but isn't much louder.Do the air box mod aswell.Also a bigger start jet 72 if you can get it will help in cold starting.48 pilot jet.The pilot air and main i'm not sure but ask indy.Once i rejjetted it made such a difference especially on hills.


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