Help! YZ426f won't start!

13 replies to this topic
  • 01yz426f

Posted April 11, 2016 - 05:31 PM


Hi everyone, this is my first post on here. I just bought a Yamaha yz426f at auction and it didn't start when I bought it. It's my first 4 stroke. I rebuilt the carb this weekend, put in a new spark plug (it's got spark). New air filter as well. It didn't have much fuel in it when I got it so I drained what was in it and put fresh stuff in. I've kicked this thing so many times I lost count. Even tried bump starting. Any ideas???
I'm gonna play with the fuel screw tomorrow night. I think it could be in to much. Would that cause it to not start?
Let me know what you guys think.
Thank you.

  • damnbiker94

Posted April 11, 2016 - 07:45 PM


All due respect, but did you not pull the fuel screw during the "carb rebuild"? And are you pulling out on the enrichener when trying to start it? There can be several issues causing a no start. Valve timing, clogged jets and/or carb passageways.

  • 01yz426f

Posted April 12, 2016 - 05:05 AM


Yup I pulled it out and got a new one. I also replaced the o-ring and washer and spring. But I think I didn't back it off enough. I also pulled the Enrichener out too. I put all new jets and gaskets in it too.

  • 0bigsilver6

Posted April 12, 2016 - 06:09 AM


Are you doing the proper starting procedure?

  • Krannie McKranface

Posted April 12, 2016 - 06:11 AM


Assuming you properly rebuilt the carb, and cleared the pilot jet passage and put in a new pilot jet......


If I were you, I would do a valve clearance check, and maybe even a leak-down test.


The most common problem (after carb neglect) on racing four stroke motor is a neglected valve train.


Valves 'close up' and prevent starting.

Timing chains stretch and jump, changing the cam timing.


If you pull the valve cover you can inspect both.


If the chain is really stretched (won't sit on the teeth correctly), it's had a lot of hours on it, and so has the rest of the head,  and I'd pull the head and have it rebuilt....before it's too late.


Download a factory service manual from Yamaha's website for guidance.

  • 01yz426f

Posted April 12, 2016 - 07:13 AM


yup I put a new pilot jet in it. I am pretty sure I'm doing the right starting procedure getting it top dead center. I'll take off the valve cover and check the valve clearances and timing chain. Thanks for the help!!

  • grayracer513

Posted April 12, 2016 - 08:30 AM


The starting procedure does not involve "getting it on top dead center".  If it still does not have an auto-decompression cam in it, then the procedure calls for you to find the beginning of the compression stroke, which will be "the hard spot" that you run into.  Then you pull the compression release, and push the starter lever down right about 1 inch more and then stop, let go the release, move the lever back to the top, and kick it.


The idea is NOT to pass TDC and kick through 1 1/2 revolutions to get to the next one like an old British bike.  What you want to do is to cut the compression stroke down to something you can actually kick through.  The full comp stroke starts at about 125 degrees before top, you want to move the crank to somewhere around 20-40 degrees before top, so that you can still kick through part of the compression cycle and past the ignition point.  Failing to understand this is one of the biggest problems people have with starting the old bikes.

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  • 01yz426f

Posted April 12, 2016 - 08:45 AM


So what I was doing and told to do was, pulling the decompression lever in giving it a few kicks then letting is out to find that "hard spot" once I found that then pull the lever in and go down a little (like you said) and then give it one hard kick. Does that sound right?

  • grayracer513

Posted April 12, 2016 - 09:56 AM


Roughly, except for the part about giving it a few kicks with the comp release held.  You do that to clear out a wet cylinder.  It's the opposite of what you want for a cold start.  Pull the "choke" plunger out, twist the throttle once or twice to prime the cold engine, then locate compression, move a little farther, and kick.


Also, be certain your plug is good. The YZ400/426 has a marginal amount of spark at cranking speeds, and the plugs are easy to foul.

  • 01yz426f

Posted April 12, 2016 - 10:26 AM


Alright. I'll double check the plug tonight, I just put in a new one. Thanks for the help.

  • 01yz426f

Posted April 12, 2016 - 05:42 PM


Alright I got it running. I kicked it over several times and then pulled the plug figuring it should be a little bit wet from kicking it over. It was dry, so I took the carb back off and backed the fuel screw off to 1.5 turns. Then I took the main jet out and it was on the fifth clip (which I put it on because that's the way I took the old jet out) and stock it's on supposed to be on the fourth so I changed that and put it back together. First kick and it started. I'm gonna still go through it this weekend and double check everything before I start riding it. THANK YOU GUYS for all the help. I'll come back if I've got any questions.

  • grayracer513

Posted April 13, 2016 - 06:09 AM


 Then I took the main jet out and it was on the fifth clip


That's the needle, not the main jet.

  • 01yz426f

Posted April 13, 2016 - 06:33 AM


Yeah sorry that's what I meant. Thanks

  • dirtpaw12

Posted April 13, 2016 - 08:46 AM


I had the same problem when I first got my 426. I just was not doing the procedure right. I thought I was but my foot was not positioned right on the kickstarter and was hitting the footpeg as it was coming down and the kickstarter was not going the full way down. One I figured out how to position my foot so it would not hit the footpeg (it was starting to hurt like hell) it started like a top. Takes a little playing with. 

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