BACKFIRING WHEN LETTING OFF THE GAS?



12 replies to this topic
  • Guest_Guest_*

Posted December 03, 2000 - 06:22 PM

#1

Does anyone have any ideas as to why my '98 WR400 backfires out the stock pipe (No Baffle) when I let off the throttle? It doesn't do it all the time, but enough to be annoying and I wonder if something is being damaged. I don't remember having this problem when I first got the bike.

The carb has totally stock settings with the exception of a leaner 165 Main Jet (Stock is 168).

As my previous letter indicated I too have experienced the dreaded Carb Slide plate failure as well. I hope that this was not related to the backfiring.

If anyone out there can tell me how to eliminate the backfiring problem I would surely appreciate it.

Thanks

  • Scott_F

Posted December 03, 2000 - 08:56 PM

#2

Make sure your headpipe is tight at the head. If not, your bike can make a popping sound on decel.

  • Boit

Posted December 03, 2000 - 09:42 PM

#3

If your headpipe is not leaking, you might look next at a lean condition at the idle circuit. My 426 popped terribly on decel and I couldn't tune it out with the fuel screw. The culprit was the intake boot. This is the little manifold that the carb bolts to. I discovered that when I was reinstalling my airbox and put pressure to slip it on the carb throat, the twisting motion caused the manifold to move away from the head leaving a gap where raw dirty air was being sucked into the engine creating a lean condition. If you look closely at this manifold, you will notice that it is held on by two Allen head bolts that go thru bushings press fitted into the manifold. The head of the Allen bolts are only large enough to contact the bushings only and the manifold slid over the bolts. I corrected this problem by adding a washer under the Allen bolts that were large enough to overlap the bushings and hold the manifold itself against the head. The popping completely disappeared and my carburetion is now perfect. Hope this helps.

  • Guest_Guest_*

Posted December 03, 2000 - 09:47 PM

#4

If no air leaks on exhaust or hot start stuck open etc, then I guess idle mixture is a bit lean. Turn out the fuel/mixture screw so its 2 turns out from closed. Located on bottom of carby. Would depend on what altitude etc you are at. May need to turn out more if at a higher altitude. This change means you might need to use hot start button occasionaly.

  • Guest_Guest_*

Posted December 04, 2000 - 09:10 AM

#5

I second Damians, turn out the screw 1/4 at a time and retry it, the back-fire will let the place to a constant popping, which seems normal.

  • Mech

Posted December 04, 2000 - 09:12 AM

#6

HI,
I have the same exhaust and same problem as you I have cure it with a bigger pilot and about the slide thing It will keep breaking I think it due to back pressure and I intend to machine out a stainless steel version of it. :)

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  • Guest_Guest_*

Posted December 11, 2000 - 08:04 PM

#7

Thanks for all the suggestions. I just got back in town and will try them all. Appreciate the help!

As for the carb slide, does anyone make an aftermarket slide plate that is more bulletproof?

  • tige

Posted December 14, 2000 - 01:30 PM

#8

your air/fuel mixture ratio is off

  • Lgremovals

Posted February 06, 2016 - 02:21 AM

#9

Hi all will a kxf450 oil pump fit a 2006 model. ? :)

  • Krannie McKranface

Posted February 06, 2016 - 06:54 AM

#10

Hi all will a kxf450 oil pump fit a 2006 model. ? :)

 

WFT why are you posting here



  • Krannie McKranface

Posted February 06, 2016 - 06:57 AM

#11

Does anyone have any ideas as to why my '98 WR400 backfires out the stock pipe (No Baffle) when I let off the throttle? It doesn't do it all the time, but enough to be annoying and I wonder if something is being damaged. I don't remember having this problem when I first got the bike.

The carb has totally stock settings with the exception of a leaner 165 Main Jet (Stock is 168).

As my previous letter indicated I too have experienced the dreaded Carb Slide plate failure as well. I hope that this was not related to the backfiring.

If anyone out there can tell me how to eliminate the backfiring problem I would surely appreciate it.

Thanks

 

 

You have a lean condition at closed throttle

The most common reasons:

 

Leaking header crush washer

Leaking pipe junction

Lack of muffler packing

Leaking hot start plunger (usually from corrosion)

Improperly adjusted fuel screw <<<<<<< the most common reason

Bad fuel screw oring

Pilot jet too small (over 2 turns out for max idle speed)

Missing slide plate seal

Worn out carb body/ slide no longer seals well

 

Your motor NEEDS a muffler and packing to run well

 

ALL carb'd race bikes should decel pop a little bit, all the time, or you are too rich on the fuel screw adjustment, causing a flat spot off idle



  • stevethe

Posted February 06, 2016 - 07:05 AM

#12

You have a lean condition at closed throttle
The most common reasons:
 
Leaking header crush washer
Leaking pipe junction
Lack of muffler packing
Leaking hot start plunger (usually from corrosion)
Improperly adjusted fuel screw <<<<<<< the most common reason
Bad fuel screw oring
Pilot jet too small (over 2 turns out for max idle speed)
Missing slide plate seal
Worn out carb body/ slide no longer seals well
 
Your motor NEEDS a muffler and packing to run well
 
ALL carb'd race bikes should decel pop a little bit, all the time, or you are too rich on the fuel screw adjustment, causing a flat spot off idle


Coffee, Bill. That post is from 2000.

  • Krannie McKranface

Posted February 06, 2016 - 07:22 AM

#13

Coffee, Bill. That post is from 2000.

 

OMG I need to go back to bed






 
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