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

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