wr450 backfire on decelaration


22 replies to this topic
  • davo ttt

Posted November 10, 2006 - 06:06 PM

#1

:cheers: can anyone possibly help sometimes when i back off the throttle im getting a backfire sound would anyone know possible causes

  • boer

Posted November 11, 2006 - 02:22 AM

#2

Either you have the AIS installed or are possibly running lean.

  • raistlin89

Posted November 11, 2006 - 03:03 AM

#3

you are running to lean. try 170m

  • MountainMax

Posted November 11, 2006 - 11:42 AM

#4

A larger pilot jet and/or more turns out on the adjustable fuel mixture screw will fix you up......

  • AUS_WR450

Posted November 11, 2006 - 09:44 PM

#5

Airleaks in the exhaust system around the muffler/headpipe join, even though are rare, ould be a cause of backfiring. If all else fails, might be worth a check.:cheers:

  • MarkCRF

Posted November 11, 2006 - 10:21 PM

#6

A cracked header pipe, these can sometimes be hard to see, you will have to take it off to inspect. Even if it has a small crack, don't ride the bike as it will crack more and become irrepairable. Trust me, I know.

  • davo ttt

Posted November 11, 2006 - 11:10 PM

#7

thanks all:ride: l

  • hall1012

Posted November 19, 2006 - 02:10 PM

#8

I've got a 172m, and it still backfires. I wouldn't worry about it.

  • squirrel1

Posted November 19, 2006 - 03:34 PM

#9

I've got a 172m, and it still backfires. I wouldn't worry about it.


changing a main jet wont affect backfiring on decelleration. That is where the pilot jet comes into play. try a larger pilot jet.

  • mtrablue

Posted November 19, 2006 - 04:02 PM

#10

first off, what year is your wr? if you have the ais on your bike, it will pop a bit on decel. it's not a lean condition as much as how the ais works. if you don't have the ais ('03-'04), you should consider your jetting. running a 48 pilot jet is a good base line number and should take care of the popping. if you run a 48 and do not have the ais, it will be harder to find. you will be looking for an air leak. make sure the hot start cable is not kinked and not letting the plunger seat.

  • MountainMax

Posted November 19, 2006 - 04:45 PM

#11

I have a huge pilot jet on my bike and she still backfires on decel with the fuel screw at anything less then 3 turns out, but then i get alot of black smoke on initial acceleration. can't win them all (without fuel injection)

  • JSanfilippo

Posted November 19, 2006 - 08:43 PM

#12

I have a huge pilot jet on my bike and she still backfires on decel with the fuel screw at anything less then 3 turns out, but then i get alot of black smoke on initial acceleration. can't win them all (without fuel injection)


Try one up on the pilot and one down on the main

  • davo ttt

Posted November 20, 2006 - 03:15 AM

#13

thanks again everyone:ride:

  • MountainMax

Posted November 20, 2006 - 08:42 AM

#14

im already up to a 50 pilot, never heard of anyone going any higher then that.

  • drtbk4ever

Posted November 20, 2006 - 09:24 AM

#15

first off, what year is your wr? if you have the ais on your bike, it will pop a bit on decel. it's not a lean condition as much as how the ais works. if you don't have the ais ('03-'04), you should consider your jetting. running a 48 pilot jet is a good base line number and should take care of the popping. if you run a 48 and do not have the ais, it will be harder to find. you will be looking for an air leak. make sure the hot start cable is not kinked and not letting the plunger seat.


I agree. Another thing to check for is a clogged up pilot jet. I was running a 48 and early in the year it started popping on decel, running hot, and really surging a constant low throttle speeds.
Being a newbie, I didn't know where to begin. But after many SEARCHES, I kinda narrowed it down to the pilot jet. I pulled it out and ta da, it was clogged up with gunk. Once cleaned out, the bike was back to normal.

P.S. The people here are amazing, but please do a SEARCH before asking any questions. And if you do ask a question, please provide more details about your bike.


Cheers.

  • Fullbore4

Posted November 20, 2006 - 11:34 PM

#16

I agree with someone that mentioned possible air leaks....check the header connection at the head and make sure the bracket isn't bent and the copper gasket is okay. I'd replace the copper gasket for kicks.

  • MountainMax

Posted November 21, 2006 - 02:35 PM

#17

the exhaust header? how could this cause the problem? there is no sign of black suit, which im sure would be there if it was leaking.............

  • Fullbore4

Posted November 21, 2006 - 11:02 PM

#18

Air leaks from as minor a thing as a cracked header can cause back firing. Not sure exactly why but this bike really needs to have a tight exhaust. My dealer cinched the header/exhaust bracket to tight and bent the bracket and hence caused a little leakage. I fixed it and largely reduced backfires.

I do know that carb jetting on a wr450 has little to do with backfires unless you scrap AIS and do the carb mods in "..Performance Mods" thread which effectively reduce backfiring. I have done ALL the mods listed and still have a few backfires. I have a 45 pilot....1-1/2 turns but I'm at 3500 ft.

  • emtrvt

Posted November 27, 2006 - 04:45 PM

#19

Had the same problem with my 06 wr450f. did all the free/cheap mods and new fmf pipe. got it to stop by using some high octane race fuel (112). try that

  • Fullbore4

Posted November 27, 2006 - 09:49 PM

#20

One thing I don't think has been mentioned is the float bowl vent tube In the carb bowl or the clear plastic drain tube itself could be clogged not allowing proper venting and creating a lean condition. First loosen the hex drain screw on the bottom of the carb and make sure gas runs out the clear drain tube. It is near the large (17 mm) carb drain. If it does you have to take your float bowl off and blow through the vent tube OUT to make sure it is clear. DON'T blow in or you'll push crap in the carb. All vent tubes should be clear.




 
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