Please HELP 07 yz450 WONT START



27 replies to this topic
  • sleepy514

Posted October 23, 2014 - 05:39 PM

#1

Quick run down, i got the bike from a guy on craigslist. He said the top of the motor was all new and that he replaced all the stuff himself because it dropped a valve drestroying the piston. It took him awhile to get it started when i was looking at it but he said it was out of gas so we went to the gas station and after about 3 strong kicks it started and idled and i drove it for a very short ride around the gas station before i took it home and then spent another hour trying to start it again with out any luck. he said he had about 5 hours on the new build. He also said that the exhaust cam may be off a tooth.

 

My friend owns a small engine repair shop so i dropped it off for his mechanic to look at it he tore it apart and said the piston was in backwards and the rings were upside down. he put it back together and still couldnt get it to run. He recommend i get a new timming chain and cams because he thinks either the chain is stretched or the cams may have slipped on the gears.  ALSO i found that the cams,chain, and all the valves but one are not new like the guy said that i got it from.

 

Heres where i am now, i took the bike back from the shop to look it over myself and i dont think the chain or the cams are bad and that it was more like a 400$ guess. I adjusted the valves and found that one exhaust valve was comepletely missing a shim, so now all the valves are adjusted correctly i also threw in a new spark plug, a new air filter, and i have a new chain but didnt install it unless i need to and dont think i need to just yet.

its got spark(idk if its at the right time or not) and the carb is spraying fuel and all the jets and such are free of debreis. I also did a cylinder leakage test and it seems air tight. Im not sure if i have the timming set right but i got the "I" lined up and have both cams with there dots horizontal with the case. I counted 14 pins between the top two marks on the cams. If i set it to 13 pins then one cam will be what looks like a tooth off from the mark on the head.

 

Now im not sure how tough its suppose to be to kick over but i run into a very hard tough spot when trying to kick it over but figure its as the decomp cam is slowly letting pressure out then it gives way and i can power through it. ALso im wondering if me having the vc cover off the engine would keep it from running i wouldnt think so but idk. I put the intake back on and the exhaust is on thinking they might have to be to get it to work. 

 

just to be sure but ti start it cold its

turn on gas

open choke

turn throttle 1 to 3 times

and kick like hell

 

ANy help would be great! thanks!

Erik

ill also try to get pics up of how i got it timmed.



  • Bremer120

Posted October 23, 2014 - 05:58 PM

#2

Do you have an owners manual for the bike to make certain of cam timing and ignition timing? Also if jetting is way off that could cause it not to start. Does the bike attempt to fire? It sounds like you know what you're doing and it's good you caught that valve that didn't have a shim because I think that causes the valve to drop. Anyways, have you tried to bump start the bike. I know the bike should kick start easily(mine always took one twist and one kick).

  • sleepy514

Posted October 23, 2014 - 06:06 PM

#3

i found one online and shows the marks which is where i have them but i was hung up on the whole counting pins thing. not sure about the jetting though, the guy coulda screwed with that. a few times it started and cut right off after about a second or two and starting fluid seems to help only alittle though. not tryed to bump it yet, i gotta push it in third correct? mine is a bear to kick over, i cant kick it over unless its in the right spot when the comp cam lets out some exhaust



  • Bremer120

Posted October 23, 2014 - 08:44 PM

#4

Is it harder to kick now after you had the motor apart? And actually hold off on the bump start idea there may be a reason why it's not starting and you don't want to force something. Also starter fluid isn't necessary. I've had 2 of those bikes and in any weather they both started 1st kick. How old is the gas?

  • personius264

Posted October 24, 2014 - 12:51 AM

#5

Can you post pics of your timing? Here's my 07

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  • Nautical Miles

Posted October 24, 2014 - 01:21 AM

#6

I had an issue when I was new to my bike (06). It ran great for a few months. Went to start it one day and could barely move the kickstarter and wouldn't start. Thought for sure it dropped a valve or something. Tore the head off of it.... nothing. check the valves.... nothing... looked at the carb nothing. motor spun free by hand. Didn't know what to do. Put it back together with new gaskets etc... Then the kickstarter was flying.... i thought what the hell. Tore the valve cover off again and check timing again but noticed the decompression flywheel was different. Messed with it (it was stuck engaged or in a valve open position if you will.) cycled it a few times till it moved freely and bang, started right up. every once and a while now the kickstarter will "lock up" again and i usually place it into gear and rock it back in forth and it free's up.... Now i realize my story doesn't have a whole lot of similarities to what your describing but my point is that perfect valve timing is important. If the exhaust cam is off a tooth, it will be more than enough to make starting trouble. Looking into the "common mod section" of this part of the forum reveals some important timing tips. But for me (i have rebuilt the motor and re shimmed at least 15 times now) i don't ever pay attention to the "links" or "pins", if you will. I just ensure that the crank mark lines up while in compression TDC and then ensure my cam lobes are outboard with the marks as level to the head as possible. i always install the exhaust cam first making sure all the slack is out of the chain (front of the motor) place the cam in and check my marks. then put intake in, check marks, then tensioner. rotate about 4 times and have never had a problem. I think if you have spark, and you have put in a base jetting for your elevation and setup with a clean carb, made sure your kill switch isn't holding you back, only thing left would be your compression (which if your buddy fixed the issues mentioned and your leak down was solid and so is your valve clearance) and the hole might be air tight, but not if your valves and cams are letting air out when it shouldn't, or keeping it in when it needs to let it out. 


Edited by Nautical Miles, October 24, 2014 - 01:29 AM.


  • personius264

Posted October 24, 2014 - 01:29 AM

#7

I had this problem... the machinest put my center intake valve in the wrong spot. It can be identified by the groove on the bottom of the valve

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  • sleepy514

Posted October 24, 2014 - 03:31 AM

#8

Is it harder to kick now after you had the motor apart? And actually hold off on the bump start idea there may be a reason why it's not starting and you don't want to force something. Also starter fluid isn't necessary. I've had 2 of those bikes and in any weather they both started 1st kick. How old is the gas?

no its easier than before and with the spark plug out its pretty easy.

 

Can you post pics of your timing? Here's my 07

im gona try to get some pics up today if i can

 

I had an issue when I was new to my bike (06). It ran great for a few months. Went to start it one day and could barely move the kickstarter and wouldn't start. Thought for sure it dropped a valve or something. Tore the head off of it.... nothing. check the valves.... nothing... looked at the carb nothing. motor spun free by hand. Didn't know what to do. Put it back together with new gaskets etc... Then the kickstarter was flying.... i thought what the hell. Tore the valve cover off again and check timing again but noticed the decompression flywheel was different. Messed with it (it was stuck engaged or in a valve open position if you will.) cycled it a few times till it moved freely and bang, started right up. every once and a while now the kickstarter will "lock up" again and i usually place it into gear and rock it back in forth and it free's up.... Now i realize my story doesn't have a whole lot of similarities to what your describing but my point is that perfect valve timing is important. If the exhaust cam is off a tooth, it will be more than enough to make starting trouble. Looking into the "common mod section" of this part of the forum reveals some important timing tips. But for me (i have rebuilt the motor and re shimmed at least 15 times now) i don't ever pay attention to the "links" or "pins", if you will. I just ensure that the crank mark lines up while in compression TDC and then ensure my cam lobes are outboard with the marks as level to the head as possible. i always install the exhaust cam first making sure all the slack is out of the chain (front of the motor) place the cam in and check my marks. then put intake in, check marks, then tensioner. rotate about 4 times and have never had a problem. I think if you have spark, and you have put in a base jetting for your elevation and setup with a clean carb, made sure your kill switch isn't holding you back, only thing left would be your compression (which if your buddy fixed the issues mentioned and your leak down was solid and so is your valve clearance) and the hole might be air tight, but not if your valves and cams are letting air out when it shouldn't, or keeping it in when it needs to let it out. 

ill look at the decomp cam again to see if its sticking but when i had it out i could mess with the tit on the cam and it would move the decomp lever so i think its pretty free. ill try the rock it in gear thing also, ive also tried disconnected both the nuetral switch and the kill switch but didnt seem to make a difference with them pluged in or unplugged

 

I had this problem... the machinest put my center intake valve in the wrong spot. It can be identified by the groove on the bottom of the valve

i hope the guy didnt do the valves himself, the head looks brand new and so do the srings and keepers and such but looking with a bore scope i saw that atleast 2 of the intake valves looked like they had alittle residue and the middle one looked brand new



  • Bremer120

Posted October 24, 2014 - 04:04 AM

#9

[quote name="sleepy514" post="11966521" timestamp="1414150287"]no its easier than before and with the spark plug out its pretty easy.

Ok, the only reason I ask is I started to think about the timing chain tensioner. This is also why I said avoid the bump starting idea. I couldn't remember if the tensioner could be installed incorrectly leaving the chain too tight but I could be wrong. As long as the steps in the manual were followed everything is fine. I agree with nautical miles about cam timing that's how I have always timed them, by looking at the cam lobes themselves and checking for tdc.

  • sleepy514

Posted October 24, 2014 - 04:18 AM

#10

[quote name="sleepy514" post="11966521" timestamp="1414150287"]no its easier than before and with the spark plug out its pretty easy.

Ok, the only reason I ask is I started to think about the timing chain tensioner. This is also why I said avoid the bump starting idea. I couldn't remember if the tensioner could be installed incorrectly leaving the chain too tight but I could be wrong. As long as the steps in the manual were followed everything is fine. I agree with nautical miles about cam timing that's how I have always timed them, by looking at the cam lobes themselves and checking for tdc.

ill take some photos today with the chain timmed with 13 pins across and 14 pins and to me the 14 pins look correct since both cam gears have there marks sitting right on the horizontal part of the head



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  • Slow and Jerky

Posted October 24, 2014 - 04:18 AM

#11

Make sure when you are checking your timing marks that you have tension on the chain, if the tensioner is off just push on it with your finger. My  06 jumped time once upon time (HA) and got very hard to kick over and of course wouldn't start. I would also be suspicious of the carb, if the idle jet is clogged or the passages are dirty it can make it very hard to start.



  • sleepy514

Posted October 24, 2014 - 04:50 AM

#12

Make sure when you are checking your timing marks that you have tension on the chain, if the tensioner is off just push on it with your finger. My  06 jumped time once upon time (HA) and got very hard to kick over and of course wouldn't start. I would also be suspicious of the carb, if the idle jet is clogged or the passages are dirty it can make it very hard to start.

itll stay in time even after 30 or 40 kicks from trying to start it the marks will line right back up. i pulled the carb apart and couldlnt find any dirt or clogged ports anywhere. i think the air mix screw might have been to far out though and i havent put everything back together yet to try it after screwing it all the way in and backing it out a full turn in about a qauter. but even with either it wont fire up and run, itll just chug alittle for a second or 2 then die right out. anyway i can tell if the stator is sending the signal at the right time? im guessing itll spark everytime the flywheel "I" timming mark rolls around but kick starting it and trying to see when it sparks exactly is tough. i have a 4 stroke 125 and it kicks over like a dream one kick but i assumed since this is a bigger motor that its alot tougher to kick until the exhaust cam lets the one valve open a smidge to let some compresson out. i cant just kick it right over i have to push down and feel the cam let loose some air then i can get a full kick in pretty easily.


Edited by sleepy514, October 24, 2014 - 04:51 AM.


  • sleepy514

Posted October 24, 2014 - 05:04 AM

#13

okay after watching some youtube vids of people starting there yz450s im starting to think somthings not right with mine because of how hard it is to kick over. i cant just kick it over anytime or ill run into a wall almost on the kicker and have to slowly put alot of pressure on the kicker so itll creep through im guessing the compresson then itll give way.

 

watching the cams move from the outside while slowly kicking i can tell that its when each cam lobe completely pushes down on the valves is when its very hard to kick right through but i can see the compresson cam working and hear it slowly let air out which helps me then power right through and give a decent kick

 

i wish i knew someone with a yz450 local that i could just get an idea of how tough its suppose to be to kick over


Edited by sleepy514, October 24, 2014 - 05:11 AM.


  • sleepy514

Posted October 24, 2014 - 05:52 AM

#14

somthing else just noticed and idk if its normal or not but it seems like the nipple on the decomp cam moved in slightly when it contacts the bucket for the valve, is it suppose to dip in at all or give alittle. If its not suppose to give at all then that could be why its not opening the exhaust valve enough making it alot harder to kick over. i cant get it to push in by hand but i can see when rototating the cam shafts that it goes in some when its hitting the bucket.



  • Bremer120

Posted October 24, 2014 - 10:35 AM

#15

Ok if you are pushing the kicker down and waiting for the compression to release "then" kicking this might be why it's not starting. The spark fires during the compression stroke. So if you are waiting till after that to kick then it could be possible you aren't giving it a chance to run at all. That make sense? I know the compression is hard to kick over but put the kicker to that lump or hard spot and kick smooth and long down to the peg. I know you know how to kick start a motorcycle but I always find the compression, bring the kick starter all the way up, them a smooth kick all the way down.

  • sleepy514

Posted October 24, 2014 - 02:54 PM

#16

I hear yah but theres no way I can kick through that compression stroke. Me and my buddys have tried many times and when the stroke is at difderent levels when you kick it and itl stop your foot dead to the point of hurting the sole of your foot through mx boots.

  • sleepy514

Posted October 24, 2014 - 04:45 PM

#17

Quick update, since im questioning the exhaust cam and both cams show quite a bit of wear im going to replace them both with stage 1 hotcams and after turning the motor over while watching the intake valves i noticed 2 were leaking so im gona get the whole head looked at and tested by my buddy a machinest. also im gona hone the cylinder bore since i noticed straight up and down scuffing not too deep but enough to make me wanna do somthing about it if i can while its all apart. i hope after everything is back together new cams and chain and with the valves reseated that itll fire right up or atleast be easier to kick over. ill keep updating to share if i ended up fixing the problem but somthing tells me that its probably still not gona start and that it had to do with how i was timming the engine.



  • mch

Posted October 24, 2014 - 07:51 PM

#18

It shouldn't be that hard; something is wrong.



  • personius264

Posted October 25, 2014 - 02:45 AM

#19

Could it be the Kickstart shaft?

  • sleepy514

Posted October 25, 2014 - 05:47 AM

#20

With the spark plug out it gets easier and with the head and jug off it spins free so I think it has to do with either the timming and compresson or the valves. I dont think the guy that rebuilt the head new what he was doing so hopefully when the head is torn apart ill find somthing.





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