when to rebuild YZ 426?

[Ren92]

My problem is that I can kick the bike over with out even pulling in the decomp. lever.It still has compression but not like it use to.What is weird is the last time I took it out it wasn't like that at all.Is there anything I need to check for like a broke ring or someting? ?

[NAFLASH]

Maybe the valves are out of spec.Check the valves first before tearing the motor down.

[Thumpster]

Maybe the valves are out of spec.Check the valves first before tearing the motor down.

Yes, what NAFLASH said. Do the the easy things first and check your valve adjustments. Then do a compression check before you tear into it.

[Ren92]

Well I figured I would give it a shot today and try to start it and 3 kick she came alive ?.I let it run for about 1-2min then shut it off.Tried to kick it and all was back to normal.I guess I had a valve stuck open or something.Thanks for the info though.

[sirthumpalot]

Well I figured I would give it a shot today and try to start it and 3 kick she came alive ?.I let it run for about 1-2min then shut it off.Tried to kick it and all was back to normal.I guess I had a valve stuck open or something.Thanks for the info though.

This has happened to several people, including myself. Almost no compression at all, then once you get it fired all is back to normal. This happens to me almost every time I allow a significant amount of carb cleaner to get into the cylinder, so now I try to remove the carb from the boot before hosing out the pilot circuit. ?

[Guest blatham489]

There is also the effect of oil on the rings/cylinder creating a seal. Often a compression check method will have you check it cold (dry), then squirt a little oil in the cylinder (wet) and check it again. A difference in readings indicates worn rings.

When you started it, the oil circulated and lub'ed the rings, creating a seal, hence the restored compression.

I don't plan to re-do my top end until it starts smokin'!

[Oasis_Flame]

Adjust your valves before they hit the piston. Had the same problem with a friends WR no compression. I could push the kicker down with my arm. After adjustment all the power came back.

[bushy]

My bike did that same thing, its simply a piece of carbon opening the valve a little.

[MotoX352]

course maybe your valves seats are getting worn and your valves are getting cupped mine started cuping on the intake side of things and that made me lose compression. course i just replaced all the valves, had the seats recut and replaced the piston and rings with a higher than stock compression ratio piston (13.5 - 1) and now i can stand on the kick starter by it self! lol

[yz426onNOS]

You should re-build when there is a loss of power.

[flyinguitars]

It could have been that your decompression cable or mechanisim was just stuck open too. Ive had that happen before I went to the auto decompress cam