03 Yz450f Timing Question

18 replies to this topic
  • Nathan Stiltner

Posted October 12, 2014 - 06:28 PM


I know it's a common question but which line is the TDC line on the flywheel. According to the old school method of a screwdriver in the plug hole, it would be the far right line. That's where I'm timed at. Bikes been completely rebuild top to bottom. New everything. From valves to timing chain, cylinder, piston rings, plug, carb gone thru. Have to give it a little girl to start it. Back fires while kicking. Once it starts you have to keep the throttle on a little or it dies when it idles down. Sounds just like a timing problem. Pulled the plug and it's pretty black on the end. Not bad though, but rich.
Bikes got a 48 pilot
174 main
And a 45 leak jet. Don't remember the starter jet size. Third clip down on the needle. Im in the southeast at about 3500ft give or take. Southern Virginia. Any help would be appreciated. Thanks in advance.

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  • nuity5

Posted October 12, 2014 - 07:21 PM


First possible problem I see is the cam timing. You have the marks lined up with the valve cover gasket when you should be using the surface of the head. Searching around here it appears there should be 13 pins between the 12 o'clock marks on the cams and you have 12. On the flywheel marks I can't remember if the YZ has all of the following but almost universally the marks are as follows. Turning in the normal direction of rotation the first mark will be TDC. Next mark will be firing at basically idle speed. Then there are two marks that indicate a window of maximum spark advance at higher rpm's. I'm betting cam timing is your biggest problem. 48 pilot sounds a little big to me but if it ran like that before it should run now. Clay

  • Nathan Stiltner

Posted October 12, 2014 - 08:20 PM


I haven't counted the teeth yet, but researched thru the other threads and seems to be saying the far right line is the true TDC mark. But even with the cam marks where they are, would one tooth on either or both cams make that big of a difference in starting and firing?

  • grayracer513

Posted October 13, 2014 - 07:11 AM


In your third picture, you see three radial marks.  The first two from left to right are joined by a horizontal mark; these are for ignition strobe checks.  The third one is TDC.


The mistake being made is that the cam cover gasket is still in place.  Pull it off and heck again.  Your exhaust cam is one tooth retarded by the look of things.

  • Nathan Stiltner

Posted October 13, 2014 - 07:58 AM


Thanks Grey.

  • Nathan Stiltner

Posted October 13, 2014 - 10:24 AM


I moved each cam one tooth to where the sit now. It was either a little above the cylinder head surface (which was where it was initially) or a little below which is where it is now as the picture shows. Started right up. Hard to believe one tooth either way would make that big of a difference. Now just getting the jetting right. Still doesn't idle as smooth as I think it should. A little bit of surging before it idles down. Any ideas?? My pipe is a PC T4, but I'd pretty open. I repacked it but there's a small hole around the middle mounting bong. That would probably make it hard to jet. Correct? Like I said earlier, it has a 174 main, 48 pilot and a 45 leak jet. Third clip down on the needle.

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  • grayracer513

Posted October 13, 2014 - 10:10 PM


Out of time.  The exhaust cam is one tooth advanced in that position.  Assuming you have the crank at TDC.

  • Nathan Stiltner

Posted October 13, 2014 - 10:13 PM


Its either this or the first pic I posted. Only moved it one tooth. There's no in between.

  • Nathan Stiltner

Posted October 13, 2014 - 10:14 PM


And the crank is at TDC on the far right mark as shown in the pic. Also checked the piston position with the plug out to be sure.

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  • Nathan Stiltner

Posted October 13, 2014 - 10:18 PM


You mentioned in your earlier post that my exhaust cam appeared to be retarded one tooth with the gasket still on the head. I advanced it 1 tooth to it's current position in the last pic. It is below the surface but it's either one or the other. Kinds lost as to what to do. The bike starts easily now, but still is putting some flames out the rear. But the pipe is wide open too.

  • grayracer513

Posted October 14, 2014 - 06:30 AM


You moved something two teeth, or each cam one tooth, because in the first pictures there are 12 pins between the two 12:00 o'clock marks on the cam sprockets, and in the second one there's 14.  It's supposed to come out 13.

  • Nathan Stiltner

Posted October 14, 2014 - 08:58 AM


I moved the intake cam one tooth clockwise, and moved the exhaust cam one tooth counter clockwise. So tour saying to retard my exhaust cam back one tooth and end up with 13 pins between the 12 o'clock punch marks. Correct?

  • grayracer513

Posted October 14, 2014 - 12:34 PM


Kind of, yes.  You need to move the exhaust cam back a tooth to make it line up with the head correctly.  Then you'll end up with 13 pins between them.

  • Nathan Stiltner

Posted October 14, 2014 - 02:37 PM


Ok thanks.

  • soulsedg3

Posted October 15, 2014 - 05:44 PM


Ok thanks.


Did it work Nathan?

  • Nathan Stiltner

Posted October 15, 2014 - 07:28 PM


Did it work Nathan?

Been busy today and didnt get back into the Head on the bike.. Plan on doing it tomorrow.. Will update on it tomorrow evening.. Bike starts great as is it now, but im with Grey that it prob could be better.. Might be a lot of what I thought was gonna be jetting to polish it up.. Might just be what it needs.. But I still think im gonna have to put a smaller Pilot Jet in it.. I can turn the fuel screw all the way in and the bike does'nt die.. So a smaller jet would prob be the ticket... It came stock with a 42, but when I got the bike (blown up) two years ago, it had a 40 in it for a pilot jet... Don't know what that was about... Being that it had a gutted Pro Circuit Pipe with no packing in it... But I'll post my progress...

  • grayracer513

Posted October 16, 2014 - 06:50 AM


Yes, your jetting is way too fat.  Try 168/45, needle in #4.

  • Nathan Stiltner

Posted October 21, 2014 - 10:14 AM


So I retarded the exhaust cam one tooth, which brought me to 13 pins in between the top Punch marks... Bike starts, but not easily... Took it out for the first time Sunday and had hell starting it when stalled.. I ordered a new Pipe today that will be here Friday.. Ordered the Lexx Silencer and Mid pipe... I also replaced the 48 pilot with a 45.. But it still will not idle right.. I haven't changed the clip position that Grey had suggested but am planning on doing that... Also was reading up on hanging idle which mine does.. Also the Pipe glows cherry red right out of the head seconds after starting... Damn these carb bikes.. lol  will post progress Friday....

  • TimKade

Posted October 31, 2014 - 04:09 AM


Looks like were having the same problem Nathan.

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