Will not kick start

Bought a used 2001 yz 426f last week and have ridden it twice without any problems. This past Saturday, it ran great in the morning, but that afternoon, it got to the point that it would not kick start. I drift started it and once started, it still ran great, but when the motor was shut off, you could forget about kicking it. I changed the spark plug but that didn't help. Any ideas about what this could be.


The first thing that comes to mind is the idle speed. It may be set too low.

Second thing that comes to mind, are you trying to start it like right after you stop it? You know about the hot start? pull the red choke like button out.

Thanks for the replies. I do know about the choke vs. the hot button. I even let it sit for an hour or so and tried the choke again with no luck. I will try turning the idle speed way up an see what happens.

If you are still having this problem and can supply more details, you might get some good help here. Any mods such as exhaust system? Jetting changes? What fuel do you use and what color is on the inside of your exhaust outlet? What did your spark plug look like? Just as a start of a process of elimination, I would advise to check the valve lash. All you need is one valve to be a little tight and you could experience this problem. By the way, do a quick seat-of-the-pants compression check by bringing the piston to compression and see if the kickstarter is extremely hard to kick beyond this point. I can put my 180lbs. on the lever at compression and it takes several seconds for the piston to move beyond TDC. This what you should look for.

Even after an hour, it shouldn't need the choke to start normally. The most common problem I've seen is people flooding it.


MX Tuner


Funny you should mention compression. I was just about to post another question when I saw your reply. The compression is definitely not what it was a couple of days ago. Even though I feel considerable resistance, I can move the kickstarter through several cycles with my hand. To answer your other questions, I just changed the plug (it was fouled), I have not messed with any of the carb settings so I am assuming they are factory. I use 93 octance pump gas. I now believe the problem is lack of compression, but am not where to go from here. And what bugs me even more is that the bike was screaming all day Friday and Saturday morning, and all the sudden its like I hit a brick wall. Thanks for your reply and any others would be greatly appreciated.


At this point, I think a leak-down test would be an avenue to pursue. This is a handy test/tool for a used 4-stroke MX'er. I'd like to know what you eventually find to be the culprit.

A leak down test isn't a bad idea, but before you go through that and since you're already relatively sure that the compression is less than what it should be (if you can move it with your hand without the compression release then it's definitely lacking) then check the valves. They may have been right on the edge when you got the bike and and they may have tightened up enough to hang open. My past experience with 4-strokes is that once you hit the point where a valve starts to hang open the drop in performance seems to snowball all at once. Whatever you do don't ride it until you find the cause. If the valves are hanging open then you can definitely burn a valve and/or the seat due to the leaking. Let us know what you find!

I was talking to a buddy of mine who grew up around bikes, and his initial accessment based on what I described is a problem with an exhaust value. I was thinking of going to his house this weekend and taking off the head to see what we could find. Neither he or I have done this before, but are both fairly mechanical. Anybody have any thoughts on this, pitfalls to watch out for, etc?


My only thought is do not take the head off until you have checked the valve clearances. It would be a horrible waste of time to take the head off only to find out that the valves are too tight and hanging open and could have been fixed with a simple adjustment. You have to take the valve cover off to get the head off anyway, may as well pause for a moment to check the clearances. Good luck!

Also something just sprang to mind. This probably isn't it, but while you're at it check the compression release cable to make sure it's not bound up on something or for some other reason for the compression release to be stuck partially on.

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