YZ450f 2006 wont start



14 replies to this topic
  • Yama5150

Posted August 19, 2013 - 03:15 PM

#1

Hi guys, I have an 06 Yz450 Im scratching my head on. The bike wont start, I have good compression, 2% leak down, spark is good (even replaced plug), intake lash is .178mm exhaust is .203mm (little loose on intake tight on exhaust but shouldnt prevent starting) Ive checked the timing a dozen times, compression release is working properly... Im confused that there is good compression and spark, I can see the accellerator pump squirt its shot through the carb body visually, but for my peace of mind I wanted to hear it try to fire so I sprayed starter fluid in the intake. After a dozen kicks I got a backfire, but it didnt try to run. Ive kicked it hundreds of times, but im getting nothing?? Any suggestions are appeciated! Thanks TT!



  • Dragon67

Posted August 19, 2013 - 04:17 PM

#2

When was the last time it started and what was done to it since? If it has been sitting or exposed to water it could be as simple as water in the gas or just bad gas. Could be a bad kill switch or open ground. To check the kill switch, just unplug it. For ground, you can find where the ground attaches to the frame and check the connection. Have you tried to bump start it? If it starts that way, you rule out electrical. Wonder why it's loose on intake? There are lots of reasons for no start. The couple I mentioned are easy to rule out.

  • J_YZ2fittyF

Posted August 19, 2013 - 05:02 PM

#3

When I had a loose one once, I heard such things as the valve wearing down or something....which i wasnt sure if that was right, lol. Then heard carbon possibly on the valve holding it open a little. But if you have good leakdown, doesnt seem like thatd be it either. Far as the exhaust, why is that too tight? Isn't your spec .18-.23mm

 

edit, is the yz450 diff...i just noticed you said 450...this is 250 forum, haha. Just assumed we were talkin bout a 250, lol. Or wait, title says 250f...hmm

 

Also the AP spray has nothing to do with it really. I mean in some situations you may crack the throttle a couple times, but in normal this time of yr, shouldnt have to do that. Choke should be sufficient. You arent continually cracking the throttle while you're trying to start it are you?


Edited by J_WR2fitty, August 19, 2013 - 05:05 PM.


  • Yama5150

Posted August 19, 2013 - 07:41 PM

#4

When was the last time it started and what was done to it since? If it has been sitting or exposed to water it could be as simple as water in the gas or just bad gas. Could be a bad kill switch or open ground. To check the kill switch, just unplug it. For ground, you can find where the ground attaches to the frame and check the connection. Have you tried to bump start it? If it starts that way, you rule out electrical. Wonder why it's loose on intake? There are lots of reasons for no start. The couple I mentioned are easy to rule out.

I bought it not running, but I get spark when the spark plug is out and pressed up against the head bolts so doesnt that eliminate the ignition circuit?. Fresh gas in it, it wont bump start but it back fires if I load it up while pushing it. The lose intake threw me off too, I thought for sure it was backfiring due to tight intake clearance but again Im scratching my head, Compression is good, spark seems good but Im not sure how to really verify its sparking under compression in the cylinder? But when I spray gas or starter fluid it should run for a sec even if the carb is totally shot, right?



  • Yama5150

Posted August 19, 2013 - 07:48 PM

#5

When I had a loose one once, I heard such things as the valve wearing down or something....which i wasnt sure if that was right, lol. Then heard carbon possibly on the valve holding it open a little. But if you have good leakdown, doesnt seem like thatd be it either. Far as the exhaust, why is that too tight? Isn't your spec .18-.23mm

 

edit, is the yz450 diff...i just noticed you said 450...this is 250 forum, haha. Just assumed we were talkin bout a 250, lol. Or wait, title says 250f...hmm

 

Also the AP spray has nothing to do with it really. I mean in some situations you may crack the throttle a couple times, but in normal this time of yr, shouldnt have to do that. Choke should be sufficient. You arent continually cracking the throttle while you're trying to start it are you?

The spec in my manual is .20-.25mm I get what your saying though, it shouldnt prevent it from starting. It is a 450, lol sorry F.N.G.! haha I should repost it then... but no Ive owned a few 2006 YZ450's and my starting proceedure is -pull the choke - snap the throttle once - get pressure on the kick starter - then 1 or 2 solid kicks usually fires these things up right away... this one though is being a little stubborn. Im sure its gonna be something stupid, Ive kinda verified the major stuff is working ya know? Thanks for the input



  • Yama5150

Posted August 19, 2013 - 07:58 PM

#6

Hi guys, I have an 06 Yz450 Im scratching my head on. The bike wont start, I bought it that way. I have owned a few 06 450's and have a clean starting proceedure. I have good compression, 2% leak down, spark is good (even replaced plug) strong spark when pressed against head but Im not sure how to check it in the cylinder, intake lash is .178mm exhaust is .203mm (little loose on intake tight on exhaust but shouldnt prevent starting) I verified that the valve shims are seated properly. Ive checked the timing a dozen times, compression release is working properly... Im confused that there is good compression and spark, I can see the accellerator pump squirt its shot through the carb body visually, but for my peace of mind I wanted to hear it try to fire so I sprayed starter fluid in the intake. After a dozen kicks I got a backfire, but it didnt try to run. Same when I try to bump start it, just backfires one time after loading up. Ive kicked it hundreds of times, but im getting nothing?? Any suggestions are appeciated! Thanks TT pros! 



  • J_YZ2fittyF

Posted August 19, 2013 - 08:03 PM

#7

The spec in my manual is .20-.25mm I get what your saying though, it shouldnt prevent it from starting. It is a 450, lol sorry F.N.G.! haha I should repost it then... but no Ive owned a few 2006 YZ450's and my starting proceedure is -pull the choke - snap the throttle once - get pressure on the kick starter - then 1 or 2 solid kicks usually fires these things up right away... this one though is being a little stubborn. Im sure its gonna be something stupid, Ive kinda verified the major stuff is working ya know? Thanks for the input

 

 

Yea honestly not sure where to go from there. Sure someone better suited will chime in for ya, lol. And gotcha on the 450...i have never looked @ specs for those since I have never owned/worked on one.



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  • grayracer513

Posted August 19, 2013 - 09:02 PM

#8

Verify that the TDC marked on the flywheel is actually TDC

 

Visually check the orientation of the cam lobes to detect possible sprocket slippage.

 

 

 



  • Yama5150

Posted August 19, 2013 - 09:26 PM

#9

Verify that the TDC marked on the flywheel is actually TDC

 

Visually check the orientation of the cam lobes to detect possible sprocket slippage.

ok I verified the flywheel mark is actually tdc using a zip tie in the spark plug hole, visually both cams look correct intalled at tdc, looking at the markings when comparing to photos and service manual to see if sprocket slipped but its hard to tell. I would need a degree wheel and piston stop to degree the cam though right? 



  • Dragon67

Posted August 19, 2013 - 11:27 PM

#10

The spec in my manual is .20-.25mm I get what your saying though, it shouldnt prevent it from starting. It is a 450, lol sorry F.N.G.! haha I should repost it then... but no Ive owned a few 2006 YZ450's and my starting proceedure is -pull the choke - snap the throttle once - get pressure on the kick starter - then 1 or 2 solid kicks usually fires these things up right away... this one though is being a little stubborn. Im sure its gonna be something stupid, Ive kinda verified the major stuff is working ya know? Thanks for the input


I asked Will to fix the title and move it to the 450 section. There are plenty of things you could do at this point. If you haven't tried disconnecting the kill switch, do that.

Since it was purchased not running, it would be a good idea to pop the head off for a look at the cylinder, piston and valves. Take the carbon off with Simple Green. It works great. Don't use anything but simple Green and BLUE Scotch Brite on the valves if you clean them. Definitely shim to spec. Probably due for a piston, too. Set time and also verify TDC with a screwdriver to make sure the flywheel isn't off. Replace the head gaskets. I would go through the carb to check jetting and float bowl level. I would also check all the rubber parts in the carb, including the gasket on the throttle gate, AP diaphragm, hot start plunger, o-rings on the AP, and especially the o-ring on the fuel screw. Don't hit any of those with carb cleaner, it will destroy them.

Once you button it up, if it doesn't start, it could still be electrical. Stator, CDI, coil, etc. I know you are getting spark, but is it hot enough and timed right is the question. I think doing the above first is good maintenance and will give you a better foundation, maybe even fix the problem. These high-performance 4Ts are very sensitive to jetting, timing and valve adjustment. Lots of people ignore the float bowl height. If it's too high, the bike floods and won't start. Don't overlook that. Keep us posted.

  • grayracer513

Posted August 20, 2013 - 06:09 AM

#11

To degree it, yes, but most times when a sprocket slips it moves enough to be fairly obvious.  Besides, the thing that normally causes it is a partial or momentary seizure of the cam, and that leaves damage in the bore in the head as further evidence. 

 

If you can't find a problem there, and the plug is good, the trouble is likely to be in the carb.



  • Yama5150

Posted August 23, 2013 - 12:54 AM

#12

To degree it, yes, but most times when a sprocket slips it moves enough to be fairly obvious.  Besides, the thing that normally causes it is a partial or momentary seizure of the cam, and that leaves damage in the bore in the head as further evidence. 

 

If you can't find a problem there, and the plug is good, the trouble is likely to be in the carb.

Good call, it was a slipped cam sprocket on intake and exhaust!! Lobes were pointing at 11 oclock and 1 oclock, so it wasnt obvious at first. I figured it out under bright light theres scratches on the cam end that continue onto the sprocket. You can tell where they were lined up at some point but now moved slightly. So I inspected the valves and seats which seal solvent well, I split the cases looking for evidence of sudden seizure, or something that would have caused both cams to slip. It looks like the rod is brand new, but the crank shows signs of bluing at the crank pin around lower rod bearing but I have proper rod side clearance. I really dont have anything in the budget for this bike, I was hoping to get it back together with spare gaskets and oil Ive had kicking around my garage. Im looking for a get by solution, so I was thinking I could degree the cams and make new timing marks, put it back together and click my heels for luck. Im thinking it would take something catastrophic to make the cams slip and if that happens I have much more to worry about. But the cams shouldnt slip under normal operating conditions correct? Thanks for your help BTW, everyone had good ideas, gave me something to investigate closer...



  • grayracer513

Posted August 23, 2013 - 06:45 AM

#13

I very seriously doubt that both cams have slipped, and they very rarely slip less than 15 degrees when they do.  Further, the only sort of seizure that would cause such a thing would be if the camshafts themselves seized in the head, which would be obvious.  Even if the engine were to stop instantaneously at 10K rpm, the cams would not have enough inertia to make themselves slip in the sprockets. 

 

Sounds like you're on the wrong trail.



  • Yama5150

Posted August 23, 2013 - 11:28 AM

#14

I very seriously doubt that both cams have slipped, and they very rarely slip less than 15 degrees when they do.  Further, the only sort of seizure that would cause such a thing would be if the camshafts themselves seized in the head, which would be obvious.  Even if the engine were to stop instantaneously at 10K rpm, the cams would not have enough inertia to make themselves slip in the sprockets. 

 

Sounds like you're on the wrong trail.

OK good to know, I beginning to believe this was an attempted rebuild that never fired up, not sure what parts are origional. I can tell the head had been recently cleaned of carbon and the rod is a hot rod looks like it was never used. I think the guy I bought it from tried to rebuild it and couldnt get it started,now its my problem just didnt think it would kick my ass. The exhaust cam is pushing on the valve at TDC compression with the decompression release. I need to manually disenguage the auto decomp to do a leak down test. Is that normal? The cam lobes dont look right at TDC, like 11oclock and 1 instead of 10 and 2 but the timing marks line up fine. looks like exhaust valves are opening late... Ive put so much time in this bike now and keep running into dead ends. I hope Im on the right track.



  • grayracer513

Posted August 23, 2013 - 12:02 PM

#15

On the last '06 I had apart, I degreed the exhaust cam and found that the compression release pin allowed the valve to seat at roughly 22 degrees BTDC.  It should definitely not be holding the valve open at TDC.  If your valve clearance is too tight, it will hold the exhaust valve off its seat longer than it should, but what's interesting here is that 22.5 degrees is the distance in crank degrees that the timing will change if it is moved one tooth either way.  Check the timing again.







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