2001 YZ 426 banging, popping backfireing

14 replies to this topic
  • gsa

Posted October 20, 2001 - 03:32 PM


I have a 2001 yz 426 that has been running great with stock jetting and also have done the BK mod. The bike just started backfiring during decel and now is fouling plugs. The plug color is black but dry. I can put a new plug in and it will run for 5 minutes and start popping and backfiring again. Please help!!!

  • Mook

Posted October 20, 2001 - 03:55 PM


have you done ANY maintenance to the bike lately? especially the carb? any clue would be helpfull.


  • yzernie

Posted October 20, 2001 - 03:55 PM


>What jetting are you running??
>Is your air filter clean??
>Any jetting changes since the BK mod??

--Life is too short, work hard...play hard--
Sponsored by Yamaha of Cucamonga, Larry Roeseler's Stroker Fourstroke Speed Equipment and Answer Racing, yzernie@dirtracers.com

  • gsa

Posted October 20, 2001 - 05:01 PM


I did do some rejetting at first and it ran great with the bk mod. It ran fine for 6 or 7 rides. I went to a cycle shop and picked up some new ngk8 plugs and decided i would change the six month old split fire. It ran good the next day on a day(fast track). The next time I went to ride the bike was on a night trackArena cross style). I jumped everything for about 2 laps and it started spiting and popping a little sio I pulled off. The bike then just died and would not start for about minutes. Once started I rode slowley Back to the pits and again it died. The main jet is 162, piolet stock42 air screw from 1 1/4 to 1 3/4 tried both. Air filter clean. I just finished cleaning the carb and blowing everything out and put the original plug back in and it idles fine in the garage and does not back fire at all. But it idle fine in the garage today before we went riding today. This all seemed to originaly start with a small decel pop. I also got to ride a cr450 today. nice. espesially when my bike wouldn't run. Thanks for the quick response.

  • DTRS

Posted October 20, 2001 - 05:28 PM


My 01 did that to and I checked my coil BINGO ! GOOD LUCK .

  • motobob911

Posted October 20, 2001 - 06:28 PM


I've go an '00 YZ426. Last week it was doing the same thing. It was running fine during practice. When the first moto began, it started backfiring and popping. Heavy black dry carbon on the plug and in the exhaust. One odd thing I noticed was that the exhaust had a very nasty smell. (Unburned gas?) Like you, I also tried blowing out the carb. Although the resistance for the secondary coil was right in the middle of the spec in the manual, the local dealer checked it on their Y1 tester and it indicated faulty. I just replaced the coil today and it seems to be fine now.

  • DOC

Posted October 20, 2001 - 07:30 PM


check your TPS resistance

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  • Scott_in_KC

Posted October 21, 2001 - 10:40 AM


Doc, just thought I'd let you know I had Canberra herb grilled chicken at the Outback Steakhouse last night! It was tastey, must be a nice place. Posted Image Sorry to rib you, couldn't resist, I saw your location and thought that sounds familiar?!

Ever get Kansas City strip steaks down there?? ummmmm

  • motobob911

Posted October 21, 2001 - 01:04 PM


Sorry guys, I guess I lied. I said that replacing the coil worked. I just tried to ride today and it's still backfiring and popping. I've checked the TPS resistance and it's OK. I'm buying a new stator assembly this week since the output on the pulse coil is low. I'll let you know if it works.

  • xtreme165

Posted October 22, 2001 - 03:29 AM


Try cleaning your air filter and running it with no oil at first!!!! To much air filter oil and they 400/426 wont run it will pop and sputter backfire and etc... Just try it and see could be quick fix.

  • DOC

Posted October 22, 2001 - 08:40 PM


these sure are tempermental things hey? My friends WR426 ran like that right from the word go. I think we dropped the needle two clicks (clip no.2) and it has worked fine since.
Scott, ive never had a Kansas City strip steak, and not sure if i could find it here. One day when i visit the states, i might just swing through Kansas and try one. When i do, i will tell you, and i guess that makes us even!

  • chopperman

Posted October 23, 2001 - 05:49 AM


Chceck your valves and make sure they are still in spec. Out of spec valves can cause some popping and a whole lot of other issues. Also could be in the CDI unit. Some of these 26's have bad CDI's although this was mostly on the '00 models and mostly remedied for the '01s

Originally posted by gsa:
I have a 2001 yz 426 that has been running great with stock jetting and also have done the BK mod. The bike just started backfiring during decel and now is fouling plugs. The plug color is black but dry. I can put a new plug in and it will run for 5 minutes and start popping and backfiring again. Please help!!!

  • Taffy

Posted October 23, 2001 - 12:47 PM


using a freshly oiled airfilter is a real favourite.

i've had a loose wire on the coil.

can you describe your jetting (std) and changes made.

another one is the blocked carb pipe.

i'd blow that carb out once more to be sure.


[This message has been edited by Taffy (edited October 23, 2001).]

  • gsa

Posted October 23, 2001 - 04:16 PM


Thanks for all the info. I took the carb apart and cleaned it and blew it out with a air hose. I just rode the bike for about 30 minutes then killed it and let it cool off and started it back up on the first kick and it ran great. I guess a piece of trash was somewhere in the carb.
Thanks for the help.

  • zack_attack190

Posted October 29, 2001 - 04:20 AM


I would check the carb manafold for a crack
or the clamp my be loose.

IN either case air leaks are not good. My
had a split in the manafold and it backfired a lot.

ZAck :)

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