2007 YZ450F starting problem

TeamPlayer
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TeamPlayer
Edited Date/Time 1/27/2012 6:25pm
I have a 2007 YZ450F. I have just finished cleaning the carburetor and reassembling the bike. I replaced the air filter (which was extremely dirty) and put in a new one. The bike has spark but will not fire. I tried pull starting the bike but that didn't work. The bike won't start. Can anyone help me?
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lumpy790
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lumpy790 6/23/2011 5:28am
6/23/2011 5:28am Edited Date/Time 6/23/2011 5:32am
what is your starting procedure?

Mine is:
1 choke
2 blip throtle 1 time to prime
3 grab front brake lever and squeeze it hard. (This stops you from blipping the throttle while kicking.)
4 kick it hard
5 when it fires let it idle for 30 seconds
xnationalwrench 6/23/2011 7:56am
6/23/2011 7:56am Edited Date/Time 6/24/2011 10:34am
Spark, Fuel, Compression. Since you say you have spark get a new plug, remove the old plug and put a thimble of gas into the head, install the new plug and if everything else is good you should get a pop or at least the engine should try to fire. If it doesn't it sounds like compression, if it at least tries to start it sounds like the carb/fuel circuit.
lumpy790
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lumpy790 6/23/2011 10:10am
6/23/2011 10:10am
How about a little history on the bike? Is it New to you? Why did you clean the carb?

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TeamPlayer
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TeamPlayer 6/23/2011 12:18pm
6/23/2011 12:18pm Edited Date/Time 6/23/2011 12:25pm
MOTODAD422 wrote:
Try a new plug,check valve clearance,
If the spark plug is working why would I need a new spark plug? I cleaned the carb because I thought that would be the first problem. But I didn't find anything wrong with the carb. I was doing a clean up job so I also changed the air filter and the oil (but I may have over filled the oil). The valve clearence is slightly but that shouldn't keep it from starting.
lumpy790
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lumpy790 6/24/2011 6:14am
6/24/2011 6:14am
a spark plug can fire at atmospheric pressure but not under compression.

I don't know why anyone would remove a spark plug and put the old part back in. If your questioning it......replace it.

Valve is......slightly what? Tight? Loose? Yes it can and will keep it from starting......its that old compression thing.

How much time is on the bike? Last time you put a piston & rings in it? Last time the valves were adjusted to put them in spec? Last time it ran? Is there gas in it?
MOTODAD422
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MOTODAD422 6/24/2011 12:28pm
6/24/2011 12:28pm
Thanks Lumpy i was gonna go over the whole atmospheric and compression thing about plugs.
lumpy790
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lumpy790 6/24/2011 12:40pm
6/24/2011 12:40pm
Yep learned that lesson the hard way wrenching at a shop. 1st thing I do now is replace the plug..... Amazing how many times it fixes a problem.
TeamPlayer
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TeamPlayer 6/24/2011 2:36pm
6/24/2011 2:36pm
lumpy790 wrote:
a spark plug can fire at atmospheric pressure but not under compression. I don't know why anyone would remove a spark plug and put the old...
a spark plug can fire at atmospheric pressure but not under compression.

I don't know why anyone would remove a spark plug and put the old part back in. If your questioning it......replace it.

Valve is......slightly what? Tight? Loose? Yes it can and will keep it from starting......its that old compression thing.

How much time is on the bike? Last time you put a piston & rings in it? Last time the valves were adjusted to put them in spec? Last time it ran? Is there gas in it?
Okay sorry. It's not the valves it's the valve lifter and adjusting disks that are slightly off. Both have a little less space than they should between the valve lifters and the adjusting disks. However the mechanic said this shouldn't stop the bike from starting.

I'm am not the first owner of this bike. The bike doesn't have a lot of time on it. It started showing trouble in Ocotillo Wells last summer when it just died and wouldn't start up again. We brought it back to Reno and changed the spark plug. It started up and we road for a little bit but then it just stopped. I took the bike apart to get to the carb and spotted an extremely dirty air filter. I cleaned the carb and reassembled the bike with a new air filter.

Could the coil be the problem and not the spark plug? However, I can see a spark on the spark plug so it's not dead.
Should I try manualy squirting gas through the spark plug whole to try and get the bike to fire?
lumpy790
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lumpy790 6/24/2011 5:16pm
6/24/2011 5:16pm
If your valve clearance is tight as you describe it can keep it from reaching proper compression to start. Tight valves are a sign of other problems coming requiring new valves, springs and re-cutting the head valve seats. Your air filter comment could have been the beginning of the valves end. A dirty air filter will let dirt past and the grit wears the intake valves.

I am going to guess you dont have any/much experience wrenching on your bike by your comments. Thats OK..... we all had to learn.

REPLACE THE SPARK PLUG! Its cheap and can be the whole problem.

Air filters can be cleaned and re-oiled.......they rarely need to be replaced.

Coils rarely go bad but.........My own 08 YZ450F just had the stator go bad.
MOTODAD422
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MOTODAD422 6/24/2011 5:55pm
6/24/2011 5:55pm
lumpy790 wrote:
If your valve clearance is tight as you describe it can keep it from reaching proper compression to start. Tight valves are a sign of other...
If your valve clearance is tight as you describe it can keep it from reaching proper compression to start. Tight valves are a sign of other problems coming requiring new valves, springs and re-cutting the head valve seats. Your air filter comment could have been the beginning of the valves end. A dirty air filter will let dirt past and the grit wears the intake valves.

I am going to guess you dont have any/much experience wrenching on your bike by your comments. Thats OK..... we all had to learn.

REPLACE THE SPARK PLUG! Its cheap and can be the whole problem.

Air filters can be cleaned and re-oiled.......they rarely need to be replaced.

Coils rarely go bad but.........My own 08 YZ450F just had the stator go bad.
I have had stators test good only to learn by replacing it with a known good one that it was the fault.I then did my own experiment by hooking up an analog ohm meter to it showing the correct resistance and heating it up with a hair dryer and watching it fail.
TeamPlayer
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TeamPlayer 6/25/2011 12:56pm
6/25/2011 12:56pm
lumpy790 wrote:
If your valve clearance is tight as you describe it can keep it from reaching proper compression to start. Tight valves are a sign of other...
If your valve clearance is tight as you describe it can keep it from reaching proper compression to start. Tight valves are a sign of other problems coming requiring new valves, springs and re-cutting the head valve seats. Your air filter comment could have been the beginning of the valves end. A dirty air filter will let dirt past and the grit wears the intake valves.

I am going to guess you dont have any/much experience wrenching on your bike by your comments. Thats OK..... we all had to learn.

REPLACE THE SPARK PLUG! Its cheap and can be the whole problem.

Air filters can be cleaned and re-oiled.......they rarely need to be replaced.

Coils rarely go bad but.........My own 08 YZ450F just had the stator go bad.
Thanks for the tip. I will try a fresh spark plug.
The air filter is a double arrangement so I doubt any dirt got past the second filter (it was clean when I took it off). However this would still be blocking air flow.
Should I try adjusting the air/fuel mixture and see if that helps?
lumpy790
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lumpy790 6/26/2011 6:07am
6/26/2011 6:07am Edited Date/Time 6/26/2011 6:08am
It ran before right? What has changed?

Motor needs - Fuel, Compression & Spark to run......whats missing?
TeamPlayer
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TeamPlayer 6/26/2011 11:51am
6/26/2011 11:51am Edited Date/Time 6/26/2011 11:53am
lumpy790 wrote:
It ran before right? What has changed?

Motor needs - Fuel, Compression & Spark to run......whats missing?
It ran fine before but than just started having problems until it just stopped.

I've replaced the spark plug and I have looked into the barrel of the carb. The spark plug is 'sparking' and the carb is squirting fuel like it should.

The only conclusions I can make are that...
A: The spark isn't strong enough and can't ignite the gas/air mixture. Therefore the coil or the magneto has a problem.
B: The gas/air mixture isn't right and won't burn. Which is unlikly because it was running fine before.

I'm hesitating on bringing it to the mechanic as this will be costly.
xnationalwrench 6/26/2011 1:49pm
6/26/2011 1:49pm Edited Date/Time 6/26/2011 1:50pm
xnationalwrench wrote:
Spark, Fuel, Compression. Since you say you have spark get a new plug, remove the old plug and put a thimble of gas into the head...
Spark, Fuel, Compression. Since you say you have spark get a new plug, remove the old plug and put a thimble of gas into the head, install the new plug and if everything else is good you should get a pop or at least the engine should try to fire. If it doesn't it sounds like compression, if it at least tries to start it sounds like the carb/fuel circuit.
This is what I posted earlier, you might try this and see what happens.
lumpy790
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lumpy790 6/26/2011 1:52pm
6/26/2011 1:52pm
OK so the bike just quit........that is a symptom you have left out.

When starting I twist the throttle 1 time to squirt/prime when cold. If the compression is good and it has spark + the prime it should fire/try to start if only for a second till the prime burns out.

I would get the valves properly adjusted. If that does not fix it I would replace the stator.
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TeamPlayer 6/26/2011 6:30pm
6/26/2011 6:30pm Edited Date/Time 6/26/2011 7:05pm
lumpy790 wrote:
OK so the bike just quit........that is a symptom you have left out. When starting I twist the throttle 1 time to squirt/prime when cold. If...
OK so the bike just quit........that is a symptom you have left out.

When starting I twist the throttle 1 time to squirt/prime when cold. If the compression is good and it has spark + the prime it should fire/try to start if only for a second till the prime burns out.

I would get the valves properly adjusted. If that does not fix it I would replace the stator.
To get to the valves and reset them I will have to disassemble the top part of the engine and take off the cylinder head including the timing chain.

Reseting the getting to the valves and fixing them will take time and reseting the timing chain may cause more problems.

Further, it seemed like I was getting back pressure from through the carb when I was kicking it with the air boot off. Should this be happening?

ps: Where is the stator on the bike? It doesn't say in the manual.

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xnationalwrench 6/26/2011 6:52pm
6/26/2011 6:52pm Edited Date/Time 6/26/2011 6:54pm
The only thing you have to trmove is the valve cover and cam shafts. I would find someone who has done this before and watch him very carefully and a service manual is needed also. The stator is located on the left hand side of the engine (under the case behind the shift lever)
MOTODAD422
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MOTODAD422 6/26/2011 7:25pm
6/26/2011 7:25pm
If you are getting a backfire out of the carb, thats a good sign that the intake valve or valves are tight.
TeamPlayer
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TeamPlayer 6/26/2011 11:43pm
6/26/2011 11:43pm Edited Date/Time 6/26/2011 11:47pm
MOTODAD422 wrote:
If you are getting a backfire out of the carb, thats a good sign that the intake valve or valves are tight.
It's not a backfire, it's just air when I kick the bike. And besides, air isn't supposed to be going back through the carb. It's supposed to go out the exhaust.

But I think I may have found the problem. The timing chain and the camshaft might be out of sink. This would cause the valves to open and close at the wrong times. However, to conferm this I will have to open the engine. I'm not sure where to start.
xnationalwrench 6/27/2011 6:31am
6/27/2011 6:31am
TransWorld had a video awhile back on checking the valve lash (when Mathes was there), see if you can locate it on their web site.
TeamPlayer
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TeamPlayer 6/30/2011 7:46pm
6/30/2011 7:46pm
xnationalwrench wrote:
TransWorld had a video awhile back on checking the valve lash (when Mathes was there), see if you can locate it on their web site.
TransWorld had a video awhile back on checking the valve lash (when Mathes was there), see if you can locate it on their web site.
No need. Problem has been resolved. The timing chain was out of time with the piston. I reset the chain.
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scooter5002 6/30/2011 8:59pm
6/30/2011 8:59pm
The problem has not been resolved. You have only found a symptom. If that chain was out of time, it's whipped. Or perhaps there's something wrong with the tensioner. Having not been into the internals of a Yamaha, I can't say for sure. You seriously need to check this issue out before you REALLY screw something up. Or yourself. Let me put it this way. Assuming you are a rider of this caliber, do you want to be in mid-flight on a 50' double and have your motor "just quit" while 2 stories off the deck? Wait, let me answer that for you. NO! Trust me, you have motor issues that need to be dealt with.
lumpy790
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lumpy790 7/1/2011 11:41am
7/1/2011 11:41am
100% agree...... it doesnt just skip a tooth.....unless you did it?
privateerconnection 7/1/2011 2:25pm
7/1/2011 2:25pm
if it jumped time then you need either a new timing chain or a new tensioner or prob both. If it did it once it will do it again and the next time you might not get lucky it can bend valves and damage alot of other parts not to mention cause u to crash and get injured.
mx5471
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mx5471 7/1/2011 5:10pm
7/1/2011 5:10pm
From a lot of years with Yamaha's, the chain guides also wear and need replacement. You do need to check it out before you ride again. A little time and a little money,no big deal. But grenade that motor.and you have a 4 year old pile of junk on your hands that's not worth what it costs to fix it.
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TerryK 7/2/2011 8:42am
7/2/2011 8:42am
Is everyone missing what the OP said about air filters? Sounds like the bike went a VERY long time without having the filter cleaned until of course the OP discovered the "very dirty air filter" when trying to track down a problem.

My guess is this engine has ingested so much dirt that it is simply worn out.
MX690
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MX690 7/4/2011 6:05am
7/4/2011 6:05am Edited Date/Time 7/4/2011 6:06am
Being an 07 YZ 450 owner myself, i know from experience that a worn and stretched timing chain will skip a tooth, i have had it happen, especially if the chain has kinks in it, and if it's stretched its probably kinked. Check your valve clearance first, if its in spec, it's fine. Then check your timing marks using your manual, you'll know straight away if it's skipped a tooth. If it's skipped a tooth, toss it out and buy a new one...... Don't know if im supposed to do this (mods help me out) go check thumpertalk, all the info you need will be there, they have photo's and all of what everything should look like.
TeamPlayer
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TeamPlayer 7/6/2011 12:12am
7/6/2011 12:12am
I took the bike out to St. Anthony Sand Dunes for 4 days and it ran reasonably well. The adjusting of the timing chain seems to have set it back where it belongs. I will most likely purchase a new chain tensioner to keep this from happening again.

PS: No dirt got into the engine. Dirty air filter was not the problem.

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