YZ400 popping on decel


8 replies to this topic
  • theclone

Posted January 26, 2006 - 02:02 PM

#1

I know I need to adjust the pilot jet, but that's as far as my knowledge goes. Anyone wanna help?

EDIT: w00t! silver member!

OK back on topic...

  • flintlock28

Posted January 26, 2006 - 04:10 PM

#2

Don't overlook the Fuel Screw.....

This time of year, with the temperature fluctuating, you can have the fuel screw off by a little bit, and she will backfire on deceleration.

I was at the track Sunday, and my bike was backfiring on decel. gave about 1/4 turn out, and no more backfiring. Try this first.

  • theclone

Posted January 26, 2006 - 04:59 PM

#3

Don't overlook the Fuel Screw.....

This time of year, with the temperature fluctuating, you can have the fuel screw off by a little bit, and she will backfire on deceleration.

I was at the track Sunday, and my bike was backfiring on decel. gave about 1/4 turn out, and no more backfiring. Try this first.

OK, that's what I thought at first, but after doing a search I thought it was the pilot jet. So how do I go about doing this? I got tired of searching through the manual, so that's why I am here. :thumbsup:

  • kawirider

Posted January 26, 2006 - 06:24 PM

#4

could be a leak in your exhaust or carburator

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  • FlashGordon

Posted January 26, 2006 - 07:40 PM

#5

Try a 48 pilot jet, with 2 turns out on the fuel screw. Made my de-accel pops go away.

  • flintlock28

Posted January 26, 2006 - 07:46 PM

#6

The Fuel screw is a recessed screw that is on the bottom of the carb., closest to the handlebars. It is a pain in the azz to adjust, since it is recesed. You generally have to get a stubby screwdriver, and then you have to grind down the screwdriver so that it's even shorter to fit.

The best $ 20 or so you can spend is for an Aftermarket fuel screw replacement, like the Zip-Ty model that I use. You simply remove the stock recessed screw, and install the Zip-Ty, which is a longer screw that has a knurled knob attached that also has graduated numbers on it. Now you no longer need to carry around a short screwdriver with you, you simply reach down and turn the Zip-Ty fuel screw by hand. It can make a big difference as to how crisp the throttle response is from idle to about 1/3 of throttle, it also will eliminate deceleration backfiring, if the carb is jetted reasonably where it should be.


http://www.ziptyraci...ryID=110&order=

  • swatcie

Posted January 26, 2006 - 08:35 PM

#7

I think it is normal for the yz400s because the one I had did the same thing. It also used to shoot flames out the exhaust lol! :thumbsup:

  • theclone

Posted January 26, 2006 - 08:48 PM

#8

The Fuel screw is a recessed screw that is on the bottom of the carb., closest to the handlebars. It is a pain in the azz to adjust, since it is recesed. You generally have to get a stubby screwdriver, and then you have to grind down the screwdriver so that it's even shorter to fit.

The best $ 20 or so you can spend is for an Aftermarket fuel screw replacement, like the Zip-Ty model that I use. You simply remove the stock recessed screw, and install the Zip-Ty, which is a longer screw that has a knurled knob attached that also has graduated numbers on it. Now you no longer need to carry around a short screwdriver with you, you simply reach down and turn the Zip-Ty fuel screw by hand. It can make a big difference as to how crisp the throttle response is from idle to about 1/3 of throttle, it also will eliminate deceleration backfiring, if the carb is jetted reasonably where it should be.


http://www.ziptyraci...ryID=110&order=

thanks! that's the info I needed. :thumbsup: :bonk:

A little off topic but I thought this was funny. I saw this on the page you linked me to:

Please note that some of the DR-Zs - streetlegal - do not have the Keihin pumper carb - at least what we've seen in California (for our stringent - read: ridiculous - emissions laws).


:thumbsup: ridiculous is an understatement

  • palmdaleRider

Posted January 26, 2006 - 09:11 PM

#9

Just a thought, try some STP carb cleaner. Mix 2-3 ounces in a tank and run fast. Might clean up some deposits. My bike use to backfire like a fiend and this sort of simple treatment has done wonders.





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