Having Troubles w/ the 426


14 replies to this topic
  • hyperlite33

Posted December 15, 2007 - 08:20 AM

#1

I bought my '01 YZ426f about a month ago and it wouldn't start once I got it home (wouldn't even try and fire). So I tried a new plug and it fired right up first kick.
I then took it to the track in 30deg weather (was excited to run it!) and let it warm up while I was getting ready and once riding it backfired/poped real bad on de-acceleration. Once it was really warm it ran great untill my chain broke (not at the master) which I have never seen happen before and ended my frosty ride.
Since then I have started it every weekend and it has started fine untill yesterday...now it tries to fire, but wont stay "lit" :banghead:
It is cold here, but it stays in a insulated garage.
Is there maybe something else going on here that I need to look at? Could I be fouling plugs that often? I did use Sta-bil in it a couple weeks ago, could that be it?

  • 642MX

Posted December 15, 2007 - 08:37 AM

#2

Whats your jetting and elevation? Take a look at the valve clearances too.

Popping is a sign of a lean condition or an air-leak. Hard starting is a sign of tight intake valves.

  • 426_kid

Posted December 15, 2007 - 09:03 AM

#3

when mine was doing that it was the plug... I know you just replaced it but id change it... the plugs for the 426's are fragile and tempermental... lol

  • motoxer667

Posted December 15, 2007 - 09:18 AM

#4

Do you have an aftermarket Exhaust on it? I would try a new plug also. If you are riding when it is that cold you will want to look at the jetting. If you got the service manual with it it has some recomendations on jetting for temp. If not I have seen the manuals on ebay.

I have a 01 yz 426. I do most of my riding in Michigan and their sound requirement is 94db and I run a WR muffler. Until I got it jetted right I fouled plugs almost everytime I rode. New plug = start on first kick

  • hyperlite33

Posted December 15, 2007 - 09:46 AM

#5

Whats your jetting and elevation? Take a look at the valve clearances too.

Popping is a sign of a lean condition or an air-leak. Hard starting is a sign of tight intake valves.


I have been waiting for it to get a little warmer out so I can check the valves as I think the cold will give an inaccurate reading.
I was going to check the jetting but there is a lot more to these 4 strokes than my 2 strokes carbs.

  • 642MX

Posted December 15, 2007 - 09:49 AM

#6

You can check the valves when its cold and get accurate measurements.

  • jbrooks26

Posted December 15, 2007 - 10:10 AM

#7

I agree with all of the posts above, I would also ensure that you are running the proper plug. I have seen too many people try different plugs and think that they are fine, if you simply replaced the plug with the same type you pulled out then I would suspect that the plug could be wrong. I have an 02 WR426 and I run the CR8EiX plug, not sure if the YZ runs the same plug or not, but I rarely foul these iridium plugs. You can check for air leaks with a little carb cleaner, just spray around all of the joints once you get it started and if the bike revs out then you found your leak. Hope this helps, good luck.

Josh

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  • hyperlite33

Posted December 15, 2007 - 10:18 AM

#8

Thanks guys for all the help...keep 'em coming!
How come it would start and now all of a sudden nothing? :banghead: It tries to fire, but doesn't "catch" whereas before I changed the plug a month ago it wouldn't even try and fire at all.
I am running the proper plug that the manual calls for also (CR8E)

  • jbrooks26

Posted December 15, 2007 - 10:41 AM

#9

Is the temperature much colder than it was a month ago? I had trouble with my 426 when it was down below 30 deg F, I determined that it was due to the oil being so thick that I could not kick it over fast enough. You kick and kick, eventually wet fouling the plug and then wearing out your leg. One thing you could try would be to place the bike in a heated room or heated garage over night or at least for several hours. Then try again, I bet you are fighting the cold engine. Hope this helps.

Josh

  • atropine

Posted December 15, 2007 - 12:04 PM

#10

I have noticed with both my 426 and my 450 that cold weather requires a little change in my air/fuel screw setting. I rode the 450 here the other day and it ran great, but then the temp dropped 30 degrees and it ran like crap (bogging, hesitation, decel popping, etc). As mentioned above, these are signs of running lean. Adjusted the air/fuel screw about 1/4 turn and it ran great. The next day I ordered a Zip-Ty fuel screw to make the job easier.

I also had a fair amount of plug fouling when I first got my 426. I found that I had to be very careful not to just start it up for a minute or two and then shut it off; it liked to be run for awhile with some real revs before shutting it down.

  • hyperlite33

Posted December 15, 2007 - 03:59 PM

#11

Thanks guys for all the input!!
I am going to leave it be since I can't ride it right now due to needing a new chain (hopefully Santa will bring me one!) and also due to the fact that the arch of my foot is bruised and feels broken from all the kicking! :busted:
I thought maybe the bike might not like teaser starts, and is getting back at me for not running it hard. :banghead:
Thinking about replacing all the vent hoses on the carb, and at that time tear it apart and clean it up and check jetting and getting a longer air/fuel screw...I love the one on my DRZ!
It's just weird to me that from one week to the other and no extreme drop in temps could cause it to have trouble starting.

  • grayracer513

Posted December 15, 2007 - 06:03 PM

#12

You realize that a 15-20 degree drop in temp wants a one step larger jet to correct for it, yes? If it was 60 and is now 30, You could probably help the situation quite a bit by going to the next larger pilot and main jets.

  • hyperlite33

Posted December 15, 2007 - 07:39 PM

#13

You realize that a 15-20 degree drop in temp wants a one step larger jet to correct for it, yes? If it was 60 and is now 30, You could probably help the situation quite a bit by going to the next larger pilot and main jets.


Thanks Gray...I just have never had a bike be that finicky on temps. My 2-stroke Banshee that is tuned for 8000' and 70deg would start second kick if I tried right now in the same garage. My experience with 4strokes seems that they take temp and elevation changes better than 2stokes also. My DRZ will start in any temp/elevation with no change in jets.:banghead:

  • grayracer513

Posted December 15, 2007 - 07:47 PM

#14

Assuming your bike was "ideally" jetted for the average conditions you use it in, the same would probably be true of your 426, too. But what if it were slightly on the lean side at the mean temperature in the first place? Either way, cold air is denser, and needs more fuel to balance it out, and your bike is acting lean, by the sound of things.

  • hyperlite33

Posted December 15, 2007 - 09:20 PM

#15

That makes sense Gray...
This is probably a dumb subject to talk about since I don't know where the jetting is at currently...the previous owner said it was "Proffesionally jetted" by the local shop, but to what temp and elevation are unknown if they even did it at all.
All I know is that once it got really warmed up that day in 30deg weather it ran great...I thought it was running some bad gas out of it since it sat for a while, but sounds like more jetting issues than gas.





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