YZ426F Won't Start After REBUILD!

Hey Everyone,

I just finished putting together my YZ426F after rebuilding it. I had to do some transmission work which involved replacing the 3rd/5th gear pinions and a shift fork. When I try and start the bike it's hard to kick. It kicks through with the decomp lever pulled it's just alot harder. Same thing when I release it to give it a good kick to start it. Thing won't start! Could it be that my timing is off?? Any help would be awesome!

Thanks

An engine will be tight until it's broken in. How hard is it to turn over?

When I kick it over to tdc and remove the cap on the case it does not show the "I" lined up so I must have messed up the timing during assembly..

I would check that the timing is correct.

When I kick it over to tdc and remove the cap on the case it does not show the "I" lined up so I must have messed up the timing during assembly..
If you aren't looking at the "I" mark, what makes you think it's TDC?

Honestly Im really confused on timing. So when I kick it till it stops I still may not be at tdc? Should I put a pencil down in the spark plug hole to find it?

When you turn the engine over and it stops against the "hard spot", that's the beginning of the compression stroke, not TDC. In fact, with manual decompression, it's about 120 degrees before TDC. If you continue to push on the crank, it will move very slowly as compression escapes past the rings, then get to a spot where it suddenly jumps forward a little, then offers resistance again. That little jump was TDC, the point where the piston stops going up and starts back down.

In order to check the timing, you need to use the mark on the crank, then check the cam position. If you doubt the mark is correct, or can't find it, then use a screwdriver down the plug hole to locate TDC. Also bear in mind that the engine turns twice for each rotation of the camshafts, so if your cams suddenly appear to be completely upside down, turn it over one more turn and line it up again.

Okay thank you! So if it is out of time it would cause it to be hard to kick & not start?

Maybe,but if you don't do the starting drill the right way, it will be hard to kick and not start even if everything is exactly right. Also, if the carburetor is not at least 90% spot on as to the idle circuit, it will be very cranky and uncooperative.

If there's any doubt about the timing, check it. Then watch these vids:

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_a.mpg

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_b.mpg

The part about how far to move the crank is critical.

Everytime I'm playing with the timing on a bike, I'll put a long zip tie down the spark plug hole. I've done it enough where I shouldn't have to use the zip tie, but I do it anyway.. the cost of a screw up/simple mistake can be avioded VERY easily, as well as the frustration that accompanies said mistake.

Cam lobes pointing opposite directions, intake lobes pointing to the back of the bike & a zip tie (or long screw driver) down the spark plug hole. Makes messing up your timing a little more difficult to accomplish !

:smirk:

I'm waiting until the first guy asks the inevitable question about cam timing on a '10. :smirk:

Timing is simple as lining up the I mark with the marks on your cam sprockets. I mark means the piston is in the right place TDC and the marks on the cam sprockets mean your cams are in the right place in relation to where the piston is in the stroke.

Make sure your cams will turn a little freely when you got it all lined up without the tensioner on the chain. There are little clips that go on the top of the CAM. They must be installed in the slots correctly or may bind up your intake or exhaust cam. the chain connects all these parts together so if one of them is binding you are not going anywhere.

I'm waiting until the first guy asks the inevitable question about cam timing on a '10. :smirk:

ok i am asking, don't got a 10 but is it different than other 4 strokes?

I've never been so stoked in my entire life! Fixed the timing which was completely backwards. Fired right up on the second kick!!!! FYI, this was my first complete tear down and rebuild so I feel pretty good...Thank you so much everyone! GRAYRACER - Thank you for everything. You put me in the right direction with my 3rd/5th gear pinions/ shift fork and my timing. RIDE ON EVERYONE!!:smirk:

ok i am asking, don't got a 10 but is it different than other 4 strokes?
Isn't it? Think about it. :smirk:
Isn't it? Think about it. :smirk:

Intake and exhaust would be reversed but i would think there are still timing marks on the crank and cam gears. I think they switched to 2 intake and 2 exhaust valves and the engine is leaning backwards a little.

Am I missing something?

Will the cam lobes point up and out?

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