Help fix my 2000 YZ426


14 replies to this topic
  • 30-A rider

Posted October 25, 2006 - 08:33 AM

#1

Ok gentlemen. I bought a 2000 YZ426 which I have started maybe 3 times in the last 5 years due to job change and a 1200 mile move. Bike was stored propperly. So I want to get on it now and problem. I can kick through the whole stroke of the engine. Typically the YZ426 comes to an abrupt halt on compression stroke, and then the starting procedure beings. My bike kicks through easily as if I was holding the decompression lever in at all times. So Im guessing the cable for decompression is stuck or the mechanism for the decompression release is stuck holding open a valve. This is my first 4 stroke, as before this I always rode 500cc 2 stroke. So naturally with human nature Im afraid of something I dont know of or have expereince with.

So any insight, suggestions, expereince from other Yamaha YZ owners.

Thanks in advance for any responses!

  • GONE1445

Posted October 25, 2006 - 08:55 AM

#2

mine will do that some times so will my uncles both 2001's and my uncle has owned his since new

usually I just hold the decomp lever open and kick it a couple times then let the decomp lever snap back a couple times and it stops doing that

for me tho it usually happens when it starts then dies a coupld time because I get to impaciant with the throttle

  • ausgeflippt13

Posted October 25, 2006 - 09:15 AM

#3

the decomp lever shouldn't be getting in the way of anything when the engine is turning. Can you kick the bike thru the full stroke?

Try turning the crank manually with the viewing window open (turn ccw) and make sure the crank spins freely w/o any hindrance.

not that this could be your problem, but recently i couldn't kick my 98 yz400 thru the full stroke, then it would just stop, as if jammed. I had just rebuilt the engine and hadn't started it yet, so i took off the head. Turns out that the front cam chain guide I had reused from the old, blown motor had been originally damaged and was bent such that the crank counterbalance was hitting it. Just a funny, semi-related story.

  • grayracer513

Posted October 25, 2006 - 11:34 AM

#4

If the compression release is at fault, you should be able to turn the engine over while touching the lever at the head and feel the valve lifter hit it each time the valve closes. I doubt that's your problem though.

What you may have is a bit of rust on the valve seats, or stuck rings. I would suggest two things:

Pull the plug and spray a bit of a good penetrating oil into the cylinder. Not WD-40, a real penetrating oil, like GM Heat Valve Lubricant & Penetrating Oil (THE best I know of), or Liquid Wrench, etc. Turn the engine through several times and let it sit a couple of hours.

Secondly, remove the cam cover and turn the engine around until the valves are all closed. (you can visually inspect the compression release this way, too) Take a wood or plastic rod small enough to fit on the valve lifters (buckets) and tap it with a hammer hard enough to make the valves bounce open and snap back shut. If they are having trouble sealing, this will often get them to seat well enough to start, after which they will straighten themselves out in short order.

Once you get it started add a tablespoon of ATF or Marvel Mystery Oil to your first tank of gas for a little additional top lube.

  • Dustin_Mabro

Posted October 25, 2006 - 12:12 PM

#5

Once you get it started add a tablespoon of ATF or Marvel Mystery Oil to your first tank of gas for a little additional top lube.




I've never heard of this before. Is this a good practice to be doing regularly or semi-regularly?

Interesting. You continue to amaze me GrayRacer.:mad:

  • cleonard

Posted October 25, 2006 - 12:53 PM

#6

Ok gentlemen. I bought a 2000 YZ426 which I have started maybe 3 times in the last 5 years due to job change and a 1200 mile move. Bike was stored propperly. So I want to get on it now and problem. I can kick through the whole stroke of the engine. Typically the YZ426 comes to an abrupt halt on compression stroke, and then the starting procedure beings. My bike kicks through easily as if I was holding the decompression lever in at all times. So Im guessing the cable for decompression is stuck or the mechanism for the decompression release is stuck holding open a valve. This is my first 4 stroke, as before this I always rode 500cc 2 stroke. So naturally with human nature Im afraid of something I dont know of or have expereince with.

So any insight, suggestions, expereince from other Yamaha YZ owners.

Thanks in advance for any responses!



If it has been sitting for a real long time, the oil drains off the rings and they stop sealing. If you pull the plug and put in just a little bit of oil, it should seal better and be harder to kick again. Another method is to lay the bike down and tip it a bit upside down so the oil in the crankcase goes into the cylinder and onto the bottom of the piston. It will reoil the rings and they can reseal.

  • cleonard

Posted October 25, 2006 - 12:55 PM

#7

I've never heard of this before. Is this a good practice to be doing regularly or semi-regularly?

Interesting. You continue to amaze me GrayRacer.:mad:


It's actually fairly common. The main downside is increased carbon buildup on the back side of the valves and inside of the combustion chamber. The upside is some lube for the valves and the top part of the cylinder that doesn't see much engine oil.

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  • grayracer513

Posted October 25, 2006 - 01:06 PM

#8

I've never heard of this before. Is this a good practice to be doing regularly or semi-regularly?

Only when it's called for, since it will contribute a bit to carbon on the valves if overdone. A lot of older engines never needed it, since they weren't able to seal oil out of the chamber as well as is common now.

Most of the time, the fuel provides all the lubrication a modern top end needs, but some racing fuels can be a little "dry", alcohol in particular, and adding some top oil can help things stay healthy.

  • GreenKLX

Posted October 25, 2006 - 01:30 PM

#9

I purchased an '01 426 about six months ago. The bike had been sitting for 7 months before I looked at it. When I looked at the bike, it had no compression, and it was easy to kick through the stroke. I got a good deal on the bike, because it wouldn't start and didn't have enough compression. After I took it home, I posted here to try and see if there may be an easy fix. I was told that if I was lucky, all I had to do was adjust the valves, but they were in spec (still are). Then, someone else said to pull the plug, and drop a few drops of oil on top of the piston. Then, while the plug is still out, cycle the motor like 50 times. This did the trick for me, and now my bike has perfect compression. Apparently the oil seal between the piston rings and cylinder wall can dry up easily on our bikes, and this recreates a seal until the motor runs and circulates and keeps its own seal.

I bet thats the problem
http://www.thumperta...4.html?t=374504

  • gem

Posted October 25, 2006 - 07:38 PM

#10

Hey the dry piston rings explanation seems logical (no wonder I did'nt think of it). My 2000 426 has done the same thing only when it has sat for awhile

  • 30-A rider

Posted October 26, 2006 - 12:40 PM

#11

the rings loosing oil seal sounds relevant.....cause when I pull in the decompression lever, it doesnt feel hunge up or binding...this is why I was worried a valve was stuck open.....but considering valve spring tension I found that hard to beleive as well.....the oil in the plug hole sounds like the trick....will try it this weekend and let the baord know what occurs. Thanks to all suggestions! Very much appretiated!

  • 1rkcooper

Posted October 28, 2006 - 03:33 PM

#12

You may also want to loosen one of the oil lines attached to the engine and ensure the oil is being pumped through the lines before you start it. You don't take it off completely, just loosen it so you can see oil leak outas you kick it over a few times. This should help lube the cylinder walls as well.

Good Luck

  • 30-A rider

Posted October 30, 2006 - 02:25 PM

#13

Thanks for all the suggestions. YOU GUYS ROCK!

Pulled the plug...dropped about 1/2 cap full of oil down the plug hole. Put the bike in 3rd gear and walked around for a couple of minutes to work the oil around the cylinder walls. Put back in my 4 year old rusty dirty plug...put in some frsh gas in the empty tank. 4th kick and it started after at least a 3 year lay up in the garage. I couldnt not believe how much compression came back with that little bit of oil. I have workled on cars and bikes before but never had this occur. Goes to show one can always learn something from others! Thanks again so much guys. It was great to tear the sh*t out of the grass in my back yard, with my wife yelling at me,,,and me not hearing her over the exhaust...It was like old times and the bike never was laid up. Smile on my face big time!:mad: :mad:

  • GreenKLX

Posted October 30, 2006 - 04:39 PM

#14

Sweet! Congrats, glad I could help. It sounds like you were as happy that the trick worked as I was.:mad: :mad: :mad:

  • Fastest1

Posted October 30, 2006 - 05:56 PM

#15

Thanks for all the suggestions. YOU GUYS ROCK!

Pulled the plug...dropped about 1/2 cap full of oil down the plug hole. Put the bike in 3rd gear and walked around for a couple of minutes to work the oil around the cylinder walls. Put back in my 4 year old rusty dirty plug...put in some frsh gas in the empty tank. 4th kick and it started after at least a 3 year lay up in the garage. I couldnt not believe how much compression came back with that little bit of oil. I have workled on cars and bikes before but never had this occur. Goes to show one can always learn something from others! Thanks again so much guys. It was great to tear the sh*t out of the grass in my back yard, with my wife yelling at me,,,and me not hearing her over the exhaust...It was like old times and the bike never was laid up. Smile on my face big time!:mad: :mad:

Electric starters usually spin the engine fast enough to pump oil throughout and overcome dryness pretty quickly. Not that it is good for the engine to spin dry. All engine building requires priming of the oil system or liberal amounts of assembly lube or both. Glad she is running!





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