Drz 400sm backfiring problems

Hello all, first time poster. Just bought this bike a few days ago it’s an 08 drz 400sm and am starting to notice it has a strange backfire at idle. I understand a little bit at decel might be normal, but at idle too?  It appears to have been jetted already, judging by the fact it has a jd jetting sticker on the bike itself. I know that it’s not an exact indicator it has but it could be. Has an FMF exhaust, it looks like a full system rather then a slip on but not entirely sure. A buddy recommended I mess with the air and fuel screw, haven’t done that yet. Just wanted to see if there was any other tips I should try. 

 

 

Is the bike on choke when it is in the video or does it idle like that normally , if it does that when idling normally (without choke) my best bet if the air fuel mixture srew setting

The choke is off in the video. I’ll give that a shot thanks!

Open mufflers like you have do not muffle well. All engines backfire, just the OEM exhaust quiets it. You should have someone skilled go over the carb, check the jetting in it and that the ACV is working properly.

You should also ensure you have no leaks in the system. A wet towel held over the end of the muffler then listen for hissing at the various connection points. Last, if the muffler has not been repacked, repack it, that helps a lot.

I'd say that is jetted very lean . I'd bet it doesn't start that great when the motor is cold needing full choke even at 70F . I have that same exhaust only mine has the insert in it so it isn't so annoyingly loud and crackly . Definately repack also .

 

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Hello all, first time poster. Just bought this bike a few days ago it’s an 08 drz 400sm and am starting to notice it has a strange backfire at idle. I understand a little bit at decel might be normal, but at idle too?  It appears to have been jetted already, judging by the fact it has a jd jetting sticker on the bike itself. I know that it’s not an exact indicator it has but it could be. Has an FMF exhaust, it looks like a full system rather then a slip on but not entirely sure. A buddy recommended I mess with the air and fuel screw, haven’t done that yet. Just wanted to see if there was any other tips I should try. 
 
 

This should be an easy fix. Could be as simple as the mixture screw adjustment or it could be that the po put on the pipe and JD sticker but left out the jet kit leaving the bike lean. An air leak is a possibility but start with simple and go from there.

Step one, watch the 3x3 mod video on YouTube. This will help you understand the parts of the carb and what should have been done when the po put on the exhaust.

Step two, check for 3x3 air box mod and to see if the access plug has been removed from the idle mixture screw.

Step 3, report back with findings.

Thanks for the input thus far. I tried Messing with the Air fuel screw, no luck still backfiring. I did see it has the 3x3 mod on it. So now I got to either have someone look at the carb to possibly get re-jetted or figure it out myself. I’ll also have to try the wet towel on the exhaust to see if it’s maybe leaking out the system. As well as I’ll look into getting it re-packed. 

Edited by Surfman1
Spelling
Thanks for the input thus far. I tried Messing with the Air fuel screw, no luck still backfiring. I did see it has the 3x3 mod on it. So now I got to either have someone look at the carb to possibly get re-jetted or figure it out myself. I’ll also have to try the wet towel on the exhaust to see if it’s maybe leaking out the system. As well as I’ll look into getting it re-packed. 

Ok, so it has the 3x3 and the fuel screw is accessible. That's good, probably means it is jetted already. Does it react at all to the fuel screw? Any change in the idle sound or speed when adjusting the screw all the way in or out to 3.5 turns?

Watch this.

I also need to mess with the AIr Fuel screw, total noob move but this whole time I think I’ve been messing with the idle screw. Its a white plastic wheel like screw.  Thanks for the help everyone. 

Listen to W1, one of the keys I use to repack the Mighty MRD.

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