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2009 YZ 250 - Won't Start

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I have a 2009 YZ 250. Took it out to the track to spin some laps and got about a lap and half in and the bike died. It sounded like it had ran out of gas. Not the case because I had put a gallon in the tank before going out.

I have done the following:

- pulling fuel line off carb to verify fuel flow out of tank: good

- turned off fuel and emptied carb via carb drain plug: good

- turned fuel back on and let fuel flow from tank through carb and out of drain plug: good

- changed spark plug and verified that I am getting a spark: good

- pulled the carb and did a thorough cleaning with carb cleaner: good

- pulled jets to verify that they are not clogged and sprayed carb cleaner through them: good

My plug is dry. I am not getting fuel to the plug. Does the carb spray fuel when the throttle is twisted? If so, that doesn't seem to occur because I had the carb pulled off the bike with the fuel like hooked to it and the throttle cable and I was getting nothing.

Anyone else have this problem? I am at a loss. I am not getting anything when I kick it over. What I do get is, on occasion is a loud swoosh noise and slight backfire pop sound. Compression seems to be the same as before it stopped running. It doesn't appear to be any different when kicking it through.

I would appreciate any help you guys can give me. Thanks in advance for the assistance.

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put everything back together as you would normally ride it,

not sure if you every tried this before... but

take it outside, and lean it on its side, almost to the point of the grip touching the ground, if you don't see fuel piss out, something is stuck on the floats on the carb start there.

: if you don't see fuel come out of the overflow, and it won't start with choke, double check all your fuel lines, breather lines. but if you said you cleaned it then so be.

check the petcock on the tank itself, i have had a piece of fuzz from a sweater stuck on petcock tube a drz 110 causing it not to get fuel.

Edit: my bad i didn't thoroughly read your post.

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Do a compression test sound like it could be a top end if it's getting gas. And look at your reeds.

The engine doesn't appear to be getting gas. Plug is dry.

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i don't think the carburator should spray fuel when your twist the throttle wide open, as you open the throttle, it raises the slide/needle assemble allowing the motor to pull air through the carb, which in turn creates little negative pressure zone across the holes that lead to your jets pulling fuel up and out from the bowl into the passing air, then mixing/entering the intake, i believe the four stroke carbs have leak jets which use a quick shot diafram to force a bunch of fuel into the carb when you snap the throttle, to prevent bogging, perhaps your thinking of this instead.

id check your reeds make sure their not chipped, if they were broken really bad it would prevent the piston from forcing the air/fuel mix into the combustion chamber, it would probably push most of it back into the carb (when you have your carb off get someone to kick it over, see if you can feel air being force out of the intake if so your reeds are done),

id also check your floats, make sure their not puncture/broken and the have free range motion, if none of this works id perhaps check your timing as well, best of luck keep us updated:thumbsup:

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i don't think the carburator should spray fuel when your twist the throttle wide open, as you open the throttle, it raises the slide/needle assemble allowing the motor to pull air through the carb, which in turn creates little negative pressure zone across the holes that lead to your jets pulling fuel up and out from the bowl into the passing air, then mixing/entering the intake, i believe the four stroke carbs have leak jets which use a quick shot diafram to force a bunch of fuel into the carb when you snap the throttle, to prevent bogging, perhaps your thinking of this instead.

id check your reeds make sure their not chipped, if they were broken really bad it would prevent the piston from forcing the air/fuel mix into the combustion chamber, it would probably push most of it back into the carb (when you have your carb off get someone to kick it over, see if you can feel air being force out of the intake if so your reeds are done),

id also check your floats, make sure their not puncture/broken and the have free range motion, if none of this works id perhaps check your timing as well, best of luck keep us updated:thumbsup:

+1 to all of this, exactly what I was thinking.

The only thing I'd add is that the low pressure that causes fuel/air to be sucked into the combustion chamber is caused by the piston moving up and down (obviously). So simply holding the throttle open isnt doing anything till you kick it over.

But anway check

- reeds

- timing

then report back

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also you can try dumping a small amount of gas through the spark plug hole if you like, I've heard of that trick never done it though

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So, apparently I was confused with the 4T carb. I thought the carb squirted fuel when twisting the throttle also on the 2T. Thank you for setting me straight on that.

I am going to pull the carb again and change out the jets just to be certain. I also have the stock reeds that I can reinstall. The stock reeds probably should be good since they only have a couple hours on them and they've been in a box in storage. I don't have anyone to help me so unless I can kick the bike and test with my hand the suction then it might just be easier to swap out the reeds.

I'll also check the float to make sure it is good. I assume that by pulling it from the carb and submersing it in either gas will do the trick as a test. If it floats and doesn't fill with fuel then it is good. I know there was movement with the float since I reset the float height.

I'll put a little bit of gas into the spark plug hole and try to kick it over also. What does this prove exactly?

On the timing, I am not sure how the bike would go from good timing to bad timing enough for the bike to not start. I am clueless about how to mess around with the time.

Thanks guys for the suggestions. I will post up once I have figured it out. If anyone has any suggestions that have not already been shared, I am all ears.

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I am at my wits end. I have again done the following:

- pulled and cleaned carb and used compressed air to blow out the ports: good

- swapped out pilot and main jets: good

- verified no issues with float: good

- removed carb and verified suction into engine by placing hand over intake and kicking over bike: good

- swapped out reeds with stock reeds: good

- tipped bike over to get fuel drain out of overflow hose: good

With all this, I got the same thing as before...a big goose egg. :smirk:

Pulled tank off and put a little bit of fuel into the spark plug hole, replaced spark plug, and kicked bike over. Got nothing. :banana::banghead:

What I do get is a loud swoosh that will periodically occur when kicking the bike through. I have no idea what that is all about.

I verified that I am getting a spark by pulling the plug and holding it against the cylinder and kick bike. I see there is a spark.

Some of you guys suggest I do something with the timing. I am clueless to what would occur the timing to not be correct or how to set it. :bonk:

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Might be that the clutch side or magneto side crankshaft main seal poped out. Happend to my RM250 when the min bearing blew.

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Also, try a new plug. Seriously. Just because its dry does not mean its not fouled.

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I feel for you bro :bonk:

In case you know any of the following I apologise in advance. I'm also not as knowledgable as some other people on this forum so feel free to correct me if I'm wrong:

The timing refers to at what point the spark plug fires. I'm not sure what it is on your bike, but on my yz125 the timing is set at 0.02"/0.5mm below top dead center. That is zero degrees.

Advancing the timing or retarding the timing (ie making it fire at a point other than 0 degrees) is something some people do for various reasons such as performance, detonation and other things.

If your timing was fine and all you did is change a top end then I'm fairly certain that you cant have changed the timing at all. Generally you can only affect your timing if you install a new (particularly aftermarket) crank or play around with the stator or flywheel. Did you clean the stator at any point maybe move it or something?

How to check your timing:

I'd highly recommend you refer to the yamaha manual as it has diagrams and instructions and also tells you what to set it at (ie for me 0.02"/0.5mm). There is also a thread in the FAQ that will help.

Essentially though what you do is get a dial guage (precise measurement tool) and screw it into the spark plug hole (most common method) and then use it to find top dead center. You then find 0.02" below TDC. You then look at notch on your flywheel, that notch should line up to the mark on your stator. If they're not lined up, you adjust the stator so that they do line up.

Done. You have now set your timing to zero degrees.

I hillbilly'ed up a dial guage to test my timing using a $15 dial gauge of ebay and an old spark plug. If you want more details let me know.

Considering though you haven't done anything to change your timing AFAIK and your plug is dry, I dont think timing is the issue.

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hmmm this is an odd one, timing could be the culprit, seems highly unlikely for such a new bike, since youve extensively gone trought the carb, i would pull the stator cover off just to verify everything is ok, make sure the cdi magneto setup it all still tight, maybe your rotor is wrecked or you sheared the woodruff key off? to check timing i believe you need a dial guage, which you set through the spark plug hole and rest it on the piston as it gets tdc, when it gets there you zero the gauge then slow role motor over (clockwise) untill you reach require spec then you adjust the cdi magneto setup untill it lines up with punch marks on the rotor, the standered spec is .18mm. hopefully you get her figured out good luck keep us posted

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Also, try a new plug. Seriously. Just because its dry does not mean its not fouled.

Yep, used a new plug. :bonk:

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...If your timing was fine and all you did is change a top end then I'm fairly certain that you cant have changed the timing at all. Generally you can only affect your timing if you install a new (particularly aftermarket) crank or play around with the stator or flywheel. Did you clean the stator at any point maybe move it or something?

Thank you tim512 for the info. I thought the same thing. I haven't touched anything that would have altered the timing.

I did a top end about 30 hours ago. I am not sure if I should do another and see if that solves the problem.

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IMO you should do the following:

- Get a new spark plug. I know you have verified spark but plugs are cheap so its worth a shot, worst case scenario you have a spark plug lol. - edit: you've already done that lol

- If the above doesnt work, buy some 'start ya bastard' aka ethanol and see if that gets it to start.

If the bike fires with ethanol then you have verified you have a carb issue. If it doesnt then you have verified your carb is not the problem / not the only problem lol.

edit: start ya bastard:

http://www.nulon.com.au/products/Aerosols/Start_Ya_Bastard_Instant_Engine_Starter/

Edited by tim512
he tried a new plug, link to start ya bastard

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At this point I would pull the plug, put a small amount of gas down the plug hole, reinstall the plug, and see if it fires up at all.

If it does, then you've proven you have a fuel issue.

If it doesn't, then you have a spark (weak or timed wrong) or a compression issue.

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At this point I would pull the plug, put a small amount of gas down the plug hole, reinstall the plug, and see if it fires up at all.

If it does, then you've proven you have a fuel issue.

If it doesn't, then you have a spark (weak or timed wrong) or a compression issue.

I put a small amount of gas down the spark plug hole, re-installed the plug, and it did not fire up. In fact it didn't appear to do anything new. Not even a hint of starting. It did make a loud swoosh sound though.

Would a compression issue really be the culprit? If it were compression then doing a top end should correct the problem, no?

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