2004 wr450 with bad backfiring issues

45 replies to this topic

Posted February 11, 2011 - 01:48 PM


First off I tried searching but don't have unlimited access to a computert, so after 20 minutes of no luck searching I decided to post. I just picked up this 2004 wr450 from the original owner. The bike is really clean and he claims the odometer has only rolled over once which would put the bike at 1800 miles. I believe him because it looks so new, it still has the factory rear sprocket and very minor paint rub by the shifter. He has only upgraded to a drd pipe and that is it, no free mods yet. He went on to explain as I was purchasing it that it had sat for 3 years without a ride. The first thing I did upon returning home was drain the gas which was way bad. I refilled with new and tried to start the bike. I got it started with the choke but it runs really bad, and will not idle once the choke is off unless you give it at least half throttle. The bike bogs when you try to accelerate for 2 to 3 seconds backfiring 4 to 5 times before it finally picks up. I figure I am just going to get all the necessary gaskets and jets and rebuild my carb. I was wondering if there are any kits on the market that contain all necessary items for a rebuild or if you guys have any suggestions on other things to do or check while I have the carb out. Any help or ideas will appreciated, thanks.

Oh yeah he siad the dealer in vegas jetted the bike for local riding but I am not sure of the size of the jet.

  • jayh300

Posted February 11, 2011 - 02:42 PM


with gas left in it like that... i would almost guarantee it is a plugged pilot jet/ circuit... I have not had much luck cleaning one either and usually replace.. but you will have to pull the carb to see what is in it, unless they remember..
did you get a manual ?


Posted February 11, 2011 - 02:51 PM


Yeah the bike came with what looks like the factory manual about an inch thick from yamaha, I am going to order the parts you specified and gaskets and start from there. It will be good to tear into this new bike and learn about the carb from the very begininng.

  • davidl9999

Posted February 11, 2011 - 02:59 PM


If you've decided to buy jets, pick up a JD Jet kit. You'll be $$ ahead instead of getting factory jets and trying to clean parts that don't clean very well and then getting a kit later. Definitely clean the carb inside and out. Do not dip the carb or take out the center gasket. It will ruin that gasket (which is not replaceable or damn hard to find if you can get your hands on one).

  • jayh300

Posted February 11, 2011 - 03:16 PM


agree with david... jd jet kits are way cool.. you really should not need any gaskets..just read the manual on it and be very careful taking it apart..
there are alot of parts in that carb... first one i pulled apart, i laid the parts out in the order they came off...


Posted February 11, 2011 - 03:40 PM


Thank you so much for the quick replies and info, I just ordered the kit and it should be here tomorrow or monday with a new tire from rmatv. Hopefully I can get this bike running and post some pictures next week.

  • William1

Posted February 11, 2011 - 04:02 PM


Not sure if the JD kit includes a new pilot, if not, be sre to get one. Do not bother to try to clean your gunked up one.


Posted February 11, 2011 - 04:15 PM


Not sure if the JD kit includes a new pilot, if not, be sre to get one. Do not bother to try to clean your gunked up one.

I hope it does or I just spent $80.00 bones for nothing, I tried calling them before I ordered but they were closed for the weekend. Could anyone confirm weather or not the kit has a pilot jet so I can cancel my order if not.

  • davidl9999

Posted February 11, 2011 - 04:36 PM


That kit is worth every penny of $80 bones, even if it didn't come with a PJ (my oops for not saying something). If the kit doesn't have a PJ, Sudco will have them: www.sudco.com. Many dealers and shops do too, although some don't stock many (if any).


Posted February 11, 2011 - 04:45 PM


Alright I will call them Monday, and if it doesn't come with the pilot jet I will order it separately. Does the jd kit come with an actual adjustable main jet or do you have to switch different jets out as you change elevation. I commonly ride from 2,000 to 10,000 feet in a single day and like the adjustable ones more than changing jets constantly.

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  • davidl9999

Posted February 11, 2011 - 04:50 PM


Switch them out through the 17mm bolt in the bottom of the bowl. No need to remove the carb to do it.

  • CanadianWR450

Posted February 12, 2011 - 02:35 PM


The JD kit does not come with a pilot jet.
It comes with 2 O-rings for the accelerator pump mod, 2 needles (red and blue), and umm...3 main jets? (memory failing me a bit there....) And of course, what your REALLY paying the $80 for...the jetting instructions...follow them to the letter, and do not try to second guess them.


Posted February 23, 2011 - 03:50 PM


Update, So I have replaced my pilot jet with a 45 instead of 40, installed my jd kit with the red needle in the 5th position and the 165 main jet. I replaced my hot start plunger and nut with an alloy one, and installed a msr fuel screw and left it a turn and a half out. And I also installed the yz throttle stop. The bike starts right away now with the electric or kick start but still it will not idle once I turn the choke off. Originally it wouldn't run with the choke off unless it was at least half throttle, but now it will run with less than an 1/8 throttle, it just won't idle on its own with my hand off the throttle. I tried adjusting the idle screw also but it didn't seem to make any difference. Could I need to replace/clean my starter jet? Also I didn't actually take the whole carb apart and clean it all, I just replaced jets so could there be a clogged passageway or something causing this issue?
Any ideas or suggestions are appreciated, Thanks

  • davidl9999

Posted February 23, 2011 - 03:54 PM


Yes, there can be a clogged passageway. If you can turn the fuelscrew all the way out (2.5 turns) and the idle doesn't rise or drop from 1 turn open, then the pilot circuit isn't working properly. Time to clean the carb.


Posted February 23, 2011 - 04:09 PM


Thanks, I will mess with the fuelscrew to check the pilot circuit tomorrow, I guess
I should have been less lazy and just cleaned the thing the first time I had it off.

  • William1

Posted February 23, 2011 - 06:11 PM


Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

  • CanadianWR450

Posted February 24, 2011 - 01:15 AM


Also, JUST in case, make sure the rubber hose that attaches your idle adjustment hose to the actual idle adjustment on the carb is intact, and working correctly to actually turn the adjuster. I remember I seemed to turn mine all the way out one time and actually seemed to "unseat" it


Posted March 09, 2011 - 10:31 PM


Update, I got the carb off and thoroughly cleaned it. I reinstalled the carb and now the bike will start and idle fine but when I ride it still backfires a lot on deceleration and seems to bog and surge really bad past 1/2 throttle. I set my jets according to the chart in the 3rd post on this thread www.thumpertalk.com/forum/showthread.php?t=411240 for 4 to 8 thousand feet and 75 to 90 degrees but test drove it at 3,500 feet and 45 degrees, would this difference cause these issues? Also, I have installed a yz throttle stop and have opened the air box for the doctor d pipe but had forgotten to cut the gray wire before I test drove it, could this have cause my problems?
Thanks for any input.

  • Sknight

Posted March 10, 2011 - 08:17 AM


Setup for 4K feet and riding at 3500 isn't a big difference but 45* isn't helping. On mine it doesn't like sucking 50* air at all. Basically it's running a bit lean for the conditions.

The backfire on decel is normal depending on how much yours is popping but I'll bet since you're running a bit lean it's worse. I doubt the wire will change much in this instance but I don't have a whole lot of experience regarding how much the map changes.

  • davidl9999

Posted March 10, 2011 - 10:50 AM


The Main Jet circuit sounds lean for 3,500' and 45* air as posted by Sknight. Go up a size on the MJ. That should help a bit. Since every bike is different, you might need 2 sizes up. The grey wire mod would probably make things seem worse since it advances the timing a bit. It doesn't cause a problem however. It's just a tuning issue, IMO.


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