possible fouling fix

59 replies to this topic
  • yamaha.dude

Posted March 17, 2002 - 10:18 PM


To clean the carbon off plugs, spray them with a good dose of oven cleaner and let them sit for 24hours, then clean them off with brake or carby cleaner... dress the tip of the electrodes and set the gap.. ready to go...

I understand that the neutral switch does two things if it feeds a signal to the CDi... It limits the revs in neutral (like we all sit there and warm our bikes up at 9,000rpm) and it affects the timing so that the bike should (should) start easier if it is in neutral... Starting in gear with the clutch in can be a drag, both on the clutch plates and your left hand having to operate both levers...



  • rvanliere

Posted March 17, 2002 - 11:17 PM


Adam , I wouldnt even mess with the BK mod until you try this mod first . My bike sarts perfect, bone stock ( no jet changes , needle clip changes, no BK Mod , I have yet to do anything ). try it and I think you will be happy . That is unless you are one of the lucky ones to never have a problem starting your bike or fouling plugs.

  • txthumper

Posted March 18, 2002 - 03:01 AM


i went out to the shop to find the wire..i found a solid blue wire and a real light colored wire almost aqua blue..which one do i disconnect?...didnt want to just start unhooking wires,


  • sbohanon

Posted March 18, 2002 - 03:24 AM


i think the neutral switch effects the timing or rev limiter so if you miss a shift, you don't hurt the motor.

  • motoman393

Posted March 18, 2002 - 04:26 AM


I will take a few pics of this mod and put some instructions on my site later today (once I get the digi cam back) BTW TXthumper it is the light blue wire (the aqua one) Later,


  • Dodger

Posted March 18, 2002 - 07:59 AM


Does anyone know if this works on WR's also??

Just curious.

Dodger :) :D

  • Shawn_Mc

Posted March 18, 2002 - 08:25 AM


I just saw in MXA Ferrys bike doesnt have the throttle postion sensor hooked up. Im beginning to think that the throttle postion sensor and the timing, and the neutral switch all work together to get make the engine run on pump gas. Plain and simple you cant get away with 12.5:1 with pump 92 fuel. Ya gotta back the timing off in certain situations. In other words, I think Yamaha overthought this deal a tad. Im thinkin that if you can run good gas, you dont need 3-D ignition mapping ie. blue wire can go bybye

  • bjhous

Posted March 18, 2002 - 12:19 PM


Bought 426 late last year hoping for 6K it would be the answer and what did I get a really nice looking lawn ornament! Fouled over a dozen plugs the first three weekends each one sooner than the last. The first weekend I had it it wouldn't start and I ran out of new plugs so out came the 85' IT200 two kicks later we we're off. I bitched every weekend to the dealer until after the fourth I gave the bike back to them (for the 2nd time) and said that I didn't want it back until it ran for at least a weekend on one plug. At first the blamed my riding than scratched their heads and ordered me a new carb at something like $1400. Idiots I should have checked the web before even going back there. To date the bike runs much better although I have still fouled two plugs this year. So am I right in assuming that the only difference will be that you could possibly over-rev the bike in neutral once I disconnect the blue wire? Thanks already for the piece of mind. :)

  • Norman

Posted March 18, 2002 - 03:13 PM


Im running on pump gas with no problems, with the racing I do going from 1st to 2nd and missing a shift, I dont think I would ever hit the rev limiter so that shouldnt be a problem. I start on the line with the bike in second and dead engine, bike starts fine. Tim Ferrys bike has no electronics on the carb at all, just like a dirt bike should be, dont know why Yamaha has to put all this crap on the production bike. I too was ready to sell but so far Im happy again.


  • motoman393

Posted March 18, 2002 - 03:32 PM


OK guys I got some pics and a write up on my website now (BTW the bikes runs and starts much better now) http://mx393.tripod.com/bluewire.html Hope this helps,


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  • h_bomb

Posted March 18, 2002 - 03:42 PM


[ March 18, 2002: Message edited by: h bomb ]

  • John_Lorenz

Posted March 18, 2002 - 03:46 PM


Motoman Motoman hes our Man
If he cant fix it
No one Can !

He MojoMan, What kinda Digital Camara ya using? :)

  • oweel

Posted March 19, 2002 - 09:55 AM


Could it be so that the weaker spark (or other timing) is necessary for the noise inspection before a race? This is tested in neutral, so I could imagine that a litle weaker spark makes the bike just the needed bit quieter. I am just guessing so don't shoot me :)


  • PMK

Posted March 19, 2002 - 08:20 PM


After looking at MM393's photos, anyone doing this mod might be better off to pull the wire from the neutral switch side of the connecter, not the CDI side of the plug. The reason being that if the wire (although taped) were to short circuit to the frame (ground) your neutral rev limiter would be set during all gear operations.

This topic of what the function of this switch does was discussed about a year back. It appears the switch provides a lower rev limit in neutral for sound testing. Once the bike is put into gear the neutral rev limiter is deactivated and the normal rev limiter functions. It is possible that the ignition timing is changed in neutral also but noone has provided a definite answer.

I pulled the switch, plunger, spring, and wire harness and went with Ty's cover ($15?). No adverse affects yet and starts good. A couple guys a year back cut the wires off at the switch and removed them from the wire harness. This was to prevent the wires from being pulled out of the switch while riding which could cause a loss of oil.

Also several people had what they thought to be CDI problems causing hard starting and fouled plugs similar to this. In the end after warranty of the CDI some were of the opinion that the fuel brand could cause the poor operation and fouled plugs. The bike would start and run great, the tank would be filled and the thing ran like crud. Try a search for something like fouled plug = foul mouth, could even be on the WR side.

  • lewichris

Posted March 20, 2002 - 12:54 PM


i bet the engineers at yamaha dont know a thing about electronics. they just put the wires there for no reason. I am still leary of cutting the grey wire on my WR. But that is just me. I will when it is paid off i guess

  • motoman393

Posted March 20, 2002 - 01:01 PM


that makes sense PMK...I may have to change mine later this week!

  • Peenton

Posted March 20, 2002 - 04:00 PM


Is this an issue just with the 01 model? If so what was the change? I've had an '00 for a year and never have fouled a plug.

  • Norman

Posted March 20, 2002 - 04:46 PM


I too had a 2000 model and never fouled a plug, I dont think it is an issue with the 2000 and back, I never had any trouble till I bought my new one.


  • Robertski

Posted March 24, 2002 - 07:40 AM



Something happened on Saturday that has never happened before. Bike starts on the very first kick of the day :)

In 8 months of ownership this has never happened. I put a new plug in about 10 days ago, went on a 50+ mile enduro, rode it a little after an oil change, and again this weekend. I've never had a plug last this long. Ever. All of this after I disconnect the SkyBlue (Japanese/Yamaha speak for Light Blue) wire. Not to mention that re-starting after killing the bike is a lot easier too.

Kudos to you Norman K. If ThumperTalk gave out Oscars you would be my nomination. Thank You for helping make my '01 426 a easier starting and a lot more enjoyable bike. And to think I almost didn't unhook the wire :D

If there are any doubters, I say try it because it's easily reversable. I say try it becuse it really works :D

Thanks again Norman,


  • Danny_Seydel

Posted March 24, 2002 - 12:27 PM


i just did this to my yz426 and it worked great!!!! It started on FIRST kick and stayed running, this is a first IT USUALLY DIES. Great job. :)

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