down gear back fire

Hi all, I've looked arround the site for info on drz 400s backfire when down gearing and I haven't come up with a definate answer. What I've been experiencing is when the bike is at high rpms and I let off the throttle, as the bike down gears the back pressure causes a popping sound like a back fire. It doesn't happen at any other time during acceleration just on decelleration. Is the bike running too rich can I make any adjustments.

Does anyone have some insite to this issue.




Poppimg is a sign of lean. What carb and what is your current jetting? Could also be an exhaust leak.

Are you talking about actual backfiring, or the deceleration popping? My bike is stock and it's always popped on deceleration. It's not a booming backfire, just popping that I contribute to the bike being on the lean side.

Regards Sonny

My bike does the same, it's really frequent like a machine gun. I also have yosh exhaust, and my dad's drz (completely stock) does the same, just a little more discretely than mine.:worthy:

The fix is the fuel screw i think, and i'm not sure what direction. Maybe somebody could input more?:D

Proper jetting is really worth the effort. Search the jetting forum. Ian

The DRZ is a bit lean from the factory. Everyone needs to invest in a jet kit and do the 3x3 mod, especially if you've changed up the exhaust.

that popping is after burn not backfire and its caused by the excessively lean condition from high engine speed and no throttle causing the high vacuum to draw from the air bleed in the carb bowl not letting in enough fuel , most carburetors have an air cut valve which is a diaphragm operated by high vacuum when the engine speed is high and the throttle plates are closed allowing the passage in the air bleed to be temporarily blocked causing rich mixture to flow for a few seconds to reduce popping, you really don't have a problem unless its excessively loud or constant you can try removing the diaphragm and cleaning the ports and it should help other wise its completely normal on decell to experience an after burn like that.

In my case popping and backfiring was due to PAIR valve thing. By removing it I got rid of the issues, but I guess you don't have one in Canadian models.

my drz 400 is a 2003 S model and its stock carb, jets and exhaust. I don't think its the exhaust its mint.

It sounds like its a common issue, it doesn't effect performance, and its not consistant. I only notice it when I'm on the throttle hard and let off to decelerate, then I hear the popping but not so loud I can't live with it. I'm sure rejeting the bike would work with the 3*3 mod, but I do alot of trail riding were there is alot of water, and I've seen what happens when water gets in the air box. My buddy went down in the water (he has the 3*3 mod) and the bike required a new head gasket. Does any one else feel the same about the 3*3 mod, or are my concerns not relevant?:D

The 3X3 mod only matters regarding a water depth difference of a few inches. Bascially, from the top of your knee cap to just under it with the 3X3. Chances are at that depth, you have other issues to worry about.

Regarding your popping, it could be an exhaust leak at the head (try a fresh gasket) or a cleaning of the carb, perhaps a fresh pilot jet abd adjustment of the fuel screw may resolve it

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

  • Similar Content

    • By Bgringo
      I've read a lot of threads about this but still haven't found exactly what I'm looking for.  I'm pulling my 2004 DRZ400S out of storage sometime this week and getting it ready for the season.  I live at 9,000 ft, but my first ride of the year is probably going to be at around 5,000 ft.  I was going to pull the 145 main jet I'm running and put in the 150 adjusting the needle from the 2 clip to the 3rd, then re-jet once I got home.  I already have the extended fuel mixture screw in place so I started thinking that I should just run the 150 jet set up and adjust the fuel screw to compensate for the higher elevation where I'll be doing most of my riding.  I will be going down in elevation for rides until late May or June depending on snowfall, but riding on the street when I'm able.  Are there any disadvantages with this?
      I'm new to posting on this forum, so please forgive me if I didn't get the right search words in and there is already a post about this.
    • By Markl5557
      I am currently running 10w 40 Belray non synthetic and I want to switch to full synthetic amsoil .... is it ok to switch from regular to synthetic? I have read it’s not safe to go from synthetic to regular can someone explain if it’s safe to go from regular to synthetic!? Thanks !
    • By RockyMtnMark
      Good Morning,
        Last night I measured my valve clearances for the very first time (I know...) on my DRZ400S.  It's a 2002 and I've owned is since 2011.  I bought it with t's got about 15,000 miles on it and most of it's miles these days are on dirt.
      Intake specs are 0.10-0.20 mm.  Exhaust specs are 0.20-0.30
      My intake valve clearances are in spec, forgot to write them down.  My exhaust valve clearances are between 0.1778 and 0.2032 which is slightly out of spec.  They are no more than 25 microns out of spec.  My question is, do I really need to shim these?  Will this kind of out-of-spec cause performance, mechanical, or other losses?  As far as I can tell, I'd have to buy a whole shim kit which is like $80.  Thanks!
    • By Zach440
      Selling my 2009 Drz400sm. Been a great bike but it’s time to let go . Not looking for any trades - spring is just around the corner ! Located in northern Virginia . Cash only $4200- willing to negotiate I have some wolfman luggage options available as well. Love to make a package deal for someone 

      -11640 miles . Mild off-road never wrecked.
      -Oil / filter changed every 1500 miles
      -New did chain , brake pads , front sprocket at 10400 miles .
      - valves checked and within spec at 10,000
      - jetted with JD kit and 3x3 mod
      -doubletake mirrors
      -waterproof usb wired and located next to Speedo
      - drc large foot pegs , barkbusters with integrated turn signals . 12oclocklabs tall delete with upgraded circuit board
      -thumpertalk case savers
      -sergeant seat (amazing) and Clarke 3.9 tank (190mile range )
      - fog lights wired in so they shut off with high beams
      -Shorai lithium battery
      -led headlight

      - stock gas tank and seat will be included

      The bike is dirty in photos and I apologize my water is currently disabled outside due to freezing temps . Radiator guards and skid plate NOT included but can be for some extra $$. Rear tire could be replaced but front is fine .
    • By tplayer100
      Currently have a 2000 drz400s work stock suspension. From my understanding this is the worst suspension the drz ever came with without even rebound damping adjustment. Therefore I'm looking for a upgrade. I'm seeing three approaches to take. First being a newer year s model suspension with dampening adjustment. A SM model USD forks and triple tree or some USD forks and triple tree from a rmz. So if you were going to upgrade what direction would you go. I currently ride off-road mostly but I do have some 17s for on road with as well so have to keep that in mind. Thanks