04 YZ450F engine rebuild HELP



21 replies to this topic
  • ban617

Posted August 30, 2015 - 07:38 PM

#1



So i bought a compleat Wesco engine rebuild kit to do top and bottom, i have replaced everything and timed my bike per the book, now i go to fire it up to break it in and no luck i can't get it to fire at all, i checked for spark and it has spark, i even went and changed the spark plug, stilll nothing. I am at the point now that i might have to bring it into the dealer and pay out the a** but i can bear to do it please help me think of things i can look for that i may have messed up on or that i missed.sorry i forgot to mention it is a 04 YZ450F everything is stock except the header it is a FMF Power Bomb, Just put it on so not sure if that could be messing with it, i don't think it should but at this point i honestly don't know where to look form here.

Thank you.

  • grayracer513

Posted August 31, 2015 - 09:43 AM

#2

If the carburetor sat for some time while the bike was apart, the pilot jet is probably at least partially clogged with dried fuel deposits.

 

Read:  http://www.thumperta...o/#entry6879695



  • ban617

Posted August 31, 2015 - 10:00 AM

#3

Thank you I will check that, also I did call a dealer and they told me I could be 180degres off on timing but can't remember how to check it, then when I was baring the engine over I noticed that the intake valve opens on the up stroke and the the exhaust opens on the down stroke, (scratching head in confusion)

  • grayracer513

Posted August 31, 2015 - 10:28 AM

#4

No, it cannot be 180 degrees off unless you timed the engine at bottom dead center instead of top.  You probably should get your advice from someone else at the dealer.

 

The only difference between one upstroke and the other is in the position of the cams, so regardless of the crankshaft, as long as you have your cam timing marks lined up at TDC, the cams have decided that that one is compression, and the other one is exhaust.  The spark fires on every stroke, so it just doesn't matter.



  • ban617

Posted August 31, 2015 - 01:15 PM

#5

Awesome thank you, I will be calling a different dealer tomorrow, I will re check everything tonight, the only other thing I was thinking was could my magnetic pickup and magneto be at the wrong clearance, I checked the Manuel and can't find anything on it.

  • ban617

Posted September 04, 2015 - 07:07 PM

#6

After checking everything, all electronic parts are in spec, and valve clearance is within spec, timing can't get much closer, and still won't start, the closes I got was one backfire right in the beginning. So I continued kicking for at least 30mins and nothing. I even took the spark plug out heated it up and dried out the cylinder, still nothing All the dealers around me want a min of $400 just to look at it. Please anyone help I am completely stumped.

  • Aka.Goose

Posted September 04, 2015 - 08:32 PM

#7

If it's got good spark and everything seems kick through smooth, it's most likely gas related...Order some gaskets/seals/o-rings from the TT store and use a service manual to guide you in tearing down the carb and rebuilding it...You did the top and bottom, may as well do the carb and then make sure the throttle cables are adjusted correctly...May as well replace the petcock too, it has some cheap plastic filters on it that go inside the fuel tank (maybe clogged?)...Is the gas fresh (or did you use gas that you had in the garage from before the rebuild?).



  • mch

Posted September 04, 2015 - 08:45 PM

#8

Check to make sure you didn't forget a rag or paper towel behind the air filter.. I once kicked a bike over for like 30 minutes before I figured it out.  :)

 

If it's not the carb, you need to double check everything.  I like to make sure I'm at top dead center by sticking a chop stick down the spark plug hole, then turn the flywheel until I feel it is at top dead and I see the marks on the flywheel.  Make sure the spark plug wire is firmly pressed down onto the spark plug.



  • ban617

Posted September 05, 2015 - 06:48 PM

#9

So after rechecking this is what everything looks like ImageUploadedByThumper Talk1441507680.568712.jpg ImageUploadedByThumper Talk1441507696.202686.jpg ImageUploadedByThumper Talk1441507706.570798.jpg

  • grayracer513

Posted September 06, 2015 - 06:33 AM

#10

Timing's fine.  



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  • rpm

Posted September 06, 2015 - 03:09 PM

#11

I don't know of it applys on this bike but on other 4 strokes the cams have 2 dots on them and the right cam intake looks correct buy the left cam there normally is a dot that lines up with the edge of the clylinder head like the right side,  check your manual and see if that's the case. Normally when your at top dead center the came lobes are at 10:00 position (exhaust) and 2:00 position for intake as you face the came gears.

 



  • mutiny5050

Posted September 08, 2015 - 10:19 AM

#12

Left cam look off by 1 tooth, try and put it to the left 1. 



  • Aka.Goose

Posted September 08, 2015 - 10:27 AM

#13

I don't know of it applys on this bike but on other 4 strokes the cams have 2 dots on them and the right cam intake looks correct buy the left cam there normally is a dot that lines up with the edge of the clylinder head like the right side,  check your manual and see if that's the case. Normally when your at top dead center the came lobes are at 10:00 position (exhaust) and 2:00 position for intake as you face the came gears.

 

Left cam look off by 1 tooth, try and put it to the left 1. 

? Timing looks fine to me? I see a vague punch dot on the left, I think it just doesn't show up much in the pic...I'm still under the impression that it sounds fuel related? (backfired when kicking over)...Did you replace the cam tensioner when doing the top and bottom rebuild? (if not, it would be a good idea)...And just to rule out that it's not fuel related, do a carb teardown, clean, replace seals, o-rings, etc. and check to make sure the cheap filters attached to the petcock (inside the gas tank) aren't clogged...


Edited by GOOSE 07 YZ450F, September 08, 2015 - 10:32 AM.


  • grayracer513

Posted September 08, 2015 - 11:08 AM

#14

Maybe I wasn't clear enough the first time. 

 

The cam timing is correct as shown in the pictures.

Attached Thumbnails

  • cams.jpg


  • ban617

Posted September 12, 2015 - 07:04 AM

#15

Sorry for the late response everyone been real busy at work, I have done a complete top and bottom end rebuild, new crank, main bearings, connecting rod, piston, rings and all gaskets, I have also gone and tested the timing tensioner per the Manuel came out good, checked valve clearances and the only one that could be a hair off is one exhaust valve, so I reshimed it to get in spec, I can get the header to heat up now but still won't fire up, I have also cleaned the carb and all jets

  • Krannie McKranface

Posted September 12, 2015 - 07:31 AM

#16

Sorry for the late response everyone been real busy at work, I have done a complete top and bottom end rebuild, new crank, main bearings, connecting rod, piston, rings and all gaskets, I have also gone and tested the timing tensioner per the Manuel came out good, checked valve clearances and the only one that could be a hair off is one exhaust valve, so I reshimed it to get in spec, I can get the header to heat up now but still won't fire up, I have also cleaned the carb and all jets

 

The passage above the pilot jet has a '90' bend in it, and clogs easily.

Ream the passage with fishing line and spray cleaner.

Also make sure your fuel screw is adjusted at approx 1.5 turns out, and your slide plate position has the hole on the bottom.

I would also clear the cylinder of all gasses by kicking a dozen times with WOT and the kill button pressed



  • ban617

Posted September 12, 2015 - 07:51 AM

#17

I will do that today and check back in with the update, thank you for the help

  • knuckleduster271

Posted September 17, 2015 - 11:54 AM

#18

I don't know if yz's are the same as wr's but you have three electrical plugs that are all the same aside from being different colors. If you get them mismatched the bike won't start but will get an occasional backfire. Another common problem after doing a top end rebuild is the possibility of a valve shim coming out of the pocket underneath the cup. This will cause you to lose compression and not allow the motor to start. Since your valves are in spec I'd say that's not your problem.

IMAG0090_zpsiukyctv9.jpg



IMAG0091_zpsfrcdh5ds.jpg

Edited by knuckleduster271, September 17, 2015 - 12:08 PM.


  • grayracer513

Posted September 17, 2015 - 12:10 PM

#19

YZ's are not the same as WR's, so the above information is inoperative.



  • knuckleduster271

Posted September 17, 2015 - 01:00 PM

#20

YZ's are not the same as WR's, so the above information is inoperative.

So the yz doesn't have these plugs? I know two go to the stator (I think one goes to the DC rectifier on the WR), another comes from the neutral switch ie think.
I would have thought the yz would have at least two of these plugs (one stator, one neutral switch) but I guess not.





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