need a bit of help gang.....baffled.

pulled the spark plug this afternoon to check its reading, reinstalled everything and went to kick it over....I still have the decomp on this '02 426, but it stroked right through the kick w/o stopping on the high spot. I can not fathom that some debris went down the plug hole and is holding up a valve. With the decomp lever pulled in, it strokes easily as it should, w/o the lever pulled it strokes through with some resistance. Prior to plug check, the bike was running excellent. The bike will not start. This is an oddity to me. The motor is bone stock also, plug was a nice medium brown. Also made sure that the decomp cable was not kinked so that it may lightly activate it. Decomp is completely closed.

Bizzare for sure

Only thing I can suggest is to get it in gear and push it back wards a full engine cycle.

I have heard of this happening on 01's and 00's Have not a clue really. Does sound that the valve is hung.

well I'll pull the valve cover and take a peek.......... sucks. I did however pop it into gear (2nd) and can make the tire roll with effort..........GRRRRRRRRRRRRR! Yamahas are the pits when it comes to spark plug checking/changing.


I did a search in the 426 forum I found a buch of stuff but here is one link

Very familure

Loss of Compression

I searched on loss of compression

Set the criteria to look at all posts

Believe me there is enough info there

had this same problem both times that I had the top end off. I guess I dislodged some carbon in the chamber which held a valve partially open. If all the valve check ok, get a mate to help you push start it. It'll fire if u get it spinning fast enough. On mine, after it started compression returned to normal. I mixed up a batch of 2 stroke fuel (about 60:1) and ran it on that for a few minutes, just in case the valve was sticking in the guide.

my $0.02 worth,


well, took the valve cover off and the cams. Then took my drift and mallet and popped the cam followers each about a dozen times and reinstalled everything. Figured that if it is grit, then it can be broken down further. Compression came up enough to get the motor lit after about 20 fast kicks. All is well again.

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