New to me 03 Yz 450 (rebuild)


108 replies to this topic
  • KJK_JR

Posted March 09, 2012 - 10:24 AM

#61

When my 09 was brand new it was a pain to start for the first few rides. My only suggestion would be a clogged pilot jet but you've said you cleaned the carb out so I don't know. Did you check all your connections/ wiring? Try disconnecting the kill switch maybe.

Edited by KJK_JR, March 09, 2012 - 10:25 AM.


  • BDubb106

Posted March 09, 2012 - 12:51 PM

#62

Yea thats the first thing I did. I greased all of the connectors as well when I reinstalled the motor as well and have GREAT spark. Hopefully the bump start trick works... he said he's had to bump start bikes after a rebuild until the motor was broken in, esp if compression was raised (which mine wasnt) after bump starting he said to let the bike idle until it was hot kinda like you would with a heat cycle and repeat a few times. Also said they usually start quite a bit easier with race fuel. So hopefully those things work. I have some time to play with it tomm so Ill post back how it goes.

  • Schpenxel

Posted March 09, 2012 - 01:09 PM

#63

tried starting fluid just to see if it would fire?

  • BDubb106

Posted March 09, 2012 - 01:11 PM

#64

No because it will TRY to fire about every 30-40 kicks but it doesnt stay running for more than 1/2 a second.

  • BBrown626

Posted March 09, 2012 - 08:37 PM

#65

sure sounds like timing. post a pic of your cams from the side. Those two dimples have to be right on the edege of the head. I think there is supposed to be six full links between the top dimples. You might be off by one tooth.

  • BDubb106

Posted March 09, 2012 - 08:41 PM

#66

sure sounds like timing. post a pic of your cams from the side. Those two dimples have to be right on the edege of the head. I think there is supposed to be six full links between the top dimples. You might be off by one tooth.


Thats what I was thinking too but 3 people have checked it including myself (2 others) and it was right when I checked it, the other two confirmed. Ill post a pic when I get around to working on it some more.

It cant jump a tooth just from kicking it over can it?

  • BBrown626

Posted March 10, 2012 - 04:24 PM

#67

It can and probably will jump if the timing chain tensioner is not installed properly. If you turn the screw fully clockwise to widthdraw the tensioner, i had one stick fully retracted.

  • BDubb106

Posted March 10, 2012 - 05:10 PM

#68

Ok, Ill check it agian just to be sure. Went and grabbed some 110 today so as of now the plan is to check timing and bump start the thing tomm. Im planning on getting this thing running tomm.

  • BDubb106

Posted March 13, 2012 - 07:49 AM

#69

So I had my mechanic buddy come over and we messed with it a little more, cleaned the carb AGAIN, checked timing AGAIN, checked valve clearances AGAIN, replaced plug AGAIN, checked spark AGAIN (its bright white just how it should be), replaced fuel AGAIN... and still nothing, any more ideas before I dump it at the shop and have them tear the whole thing down again and pay em a shit ton of money to do the work? Im just about fed up with this thing.

Edited by BDubb106, March 13, 2012 - 07:50 AM.


  • Schpenxel

Posted March 13, 2012 - 08:28 AM

#70

Tried changing out the ignition system? Or at least the CDI box?

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  • BDubb106

Posted March 13, 2012 - 10:37 AM

#71

I put the CDI on my buddies bike and his ran fine.

  • KJK_JR

Posted March 13, 2012 - 11:36 AM

#72

Did u disconnect the kill switch and try? Maybe a bad stator.

  • BDubb106

Posted March 13, 2012 - 12:32 PM

#73

Yea disconnected the kill switch... Im thinking it has to be something elec. but the bike is getting perfect spark. If the stator were bad I would think it would fire correctly.

  • idle_mind

Posted March 29, 2012 - 12:47 PM

#74

Have you checked the coil? I'm not sure if it's the same on the 450, but on my 426 the wiring connects on the bottom of the coil and the little rubber boot likes to collect water, dirt, ect. I was having to bump start mine for what seems like forever. I recently did a complete rebuild and replaced the coil and wiring harness and it fires up on the first to third kick every time. I also disconnect the wire from the coil and blow out the boot after every ride/wash.

  • BDubb106

Posted March 30, 2012 - 03:52 AM

#75

Yea I replaced the coil as well... I got it started and was able to keep it running after about 30 mins of bump starting and stalling. Luckily we had a 4 wheeler to assist in the process. It will start now but is still difficult, takes about 6-10 kicks and a few bursts of the throttle. We went through it with a fine tooth comb and it seems that valve clearances are a little on the tight side of the spec. My mechanic buddy is attributing that to the hard starting. He says once the valves "break in" for lack of technical definition it will start as normal. Runs great once its started though. At least I have 1 of my bikes ready to take on my riding trip since Im still waiting on back order parts for my 08 and still cant get my 96 running correctly. :thumbsup:

  • grayracer513

Posted March 30, 2012 - 06:41 AM

#76

...it seems that valve clearances are a little on the tight side of the spec. My mechanic buddy is attributing that to the hard starting. He says once the valves "break in" for lack of technical definition it will start as normal.


Well, first, valves that are on the tight side of the specified range are in spec, not out, and that is how the bike was originally built. Secondly, if the valves "wear in" in any way they will get tighter, which won't help matters.

If it's just a matter of cold starting, it probably wants a bigger priming shot. Twist the throttle a few times when starting cold, and crack it open very slightly as you kick it.

  • BDubb106

Posted March 30, 2012 - 06:57 AM

#77

Well, first, valves that are on the tight side of the specified range are in spec, not out, and that is how the bike was originally built. Secondly, if the valves "wear in" in any way they will get tighter, which won't help matters.

If it's just a matter of cold starting, it probably wants a bigger priming shot. Twist the throttle a few times when starting cold, and crack it open very slightly as you kick it.


You may be right and that may be the way that he explained it... I couldnt tell you. I know nothing about the top end of a 4 stroke and I only half paid attention, so I was just guessing. Ive never done any of my own work even when I had my last 450 because it didnt get ridden much. All I know is when I measured them and they were within spec. I just followed the manual to double check the work after I found that it wouldnt start. I just had the top end rebuilt by a buddy who is also a mechanic at the shop and that included replacing the valves. He said they could have been shimmed but if they need shimmed they are on their way going out? Is there any truth to that, or should I just have had them shimmed?

Your also correct about the priming shot... It seems that I need to kick the bike 1 or 2 times then twist the throttle 2 or 3 and kick it a few more and it will start. After its warm it will start right back up first kick.

Guess its time I learn to do the work on this bike as well.

  • grayracer513

Posted March 30, 2012 - 08:25 AM

#78

...All I know is when I measured (the valves) they were within spec.

Then they are in spec and don't need to be adjusted.

I just had the top end rebuilt by a buddy who is also a mechanic at the shop and that included replacing the valves. He said they could have been shimmed but if they need shimmed they are on their way going out? Is there any truth to that, or should I just have had them shimmed?


In general terms, in a new or properly rebuilt head, the valve clearance should remain as first set for a very long period, with perhaps one or two closing up 0.01-0.02 mm if the seats wear in. Then, at some point, wear will become noticeable. Whether the valves are "on their way out" depends on what you find when the adjustment is made. If you only need to go down one shim size, and later re-checking finds that the valve stayed in adjustment for 10 hours or more, it's probably just seat wear, and things are OK. If you adjust it and then 5-10 hours later you find it tight again, or if you have to go more than two shim sizes (0.10mm), they're shot.

  • BDubb106

Posted March 30, 2012 - 08:51 AM

#79

Got ya... thanks for the help. I checked them after they were replaced, only because the bike wouldnt start and everyone kept telling me to check the valves and timing since the carb was clean and a brand new jet kit installed. He recommended kibblewhite valves and springs so I ordered them and he put them in it along with a fresh piston and rings and cam chain. I dont think he was saying they needed adjusted, he was telling me something about a fresh top end being difficult to start until it is broken in but like I said I have no idea what he was talking about.

Im still trying to learn about the 4 stroke motors. Youd laugh if you knew how long it took me to figure out how to change the oil in the thing the first time, I know virtually nothing about them. I can rebuild a 2 stroke motor with my eyes closed, top to bottom, but the thumper motors just scare the crap outta me so I always just drop it off at the shop or my buddies house and he does it on the side on a sunday when the shop is closed. I sold my last one for that very reason and stuck to the familiar 2 stroke motors. How often do you recommend checking the valves? I think someone told me 5 hours. I checked them every 10 on my last yz450f.

Maybe Ill win the Mega Millions (540 million) tonight so I can just go buy a new bike everytime the top end needs rebuilt lol

  • idle_mind

Posted March 30, 2012 - 09:16 AM

#80

Maybe Ill win the Mega Millions (540 million) tonight so I can just go buy a new bike everytime the top end needs rebuilt lol

Sorry, but I've got the winning ticket here with me.. Maybe next time.

Edited by idle_mind, March 30, 2012 - 09:16 AM.






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