2009 YZ450 lost compression after 3 hours

I've only ridden the bike about 3 hours when it started to idle erratically (it idles high when you blip the throttle, but if you ride slow ,then it comes back down) and the engine would pop when chopping the throttle sometimes killing it. It's been hot, but I don't think it's that. Not overflowing the radiator.

I stopped for a couple minutes and then went to start it and the compression was about half of what it should be. I bought the bike brand new and it worked great for about the first 2 hours. Any ideas?

does the bike run ? were you able to restart it ? Is this your first four stroke ?

The compression release mechanism on these bikes is VERY effective and can make the bike feel like it has no compression.

does the bike run ? were you able to restart it ? Is this your first four stroke ?

The compression release mechanism on these bikes is VERY effective and can make the bike feel like it has no compression.

True. Sometimes mine will start when I put my foot on the kickstart and it kicks through just from the weight of my leg.

Thanks for the comments. Bike starts and it's my 4th 4-stroke dirt bike. Hot start seems to work normally. It had more compression when I let the bike sit for a bit. The weather has been hot, but the other guys weren't having problems. I'm having a mechanic friend take a look as I've done no work on 4-strokes. I hope it's something simple and will post the results. The bike is brand new and started the popping and erratic idle after the third ride. I'm using good gas and the filter is clean.

I'm a 2-stroke guy from waaaaay back.

I've had 4 YZ450's and they all do this at one point or another and 4 of my friends have the same thing happen, not sure why they do it or why it feels they have no compression, but it has never caused any issues, and they will always start and run fine. One thing that Grey suggested is that when your bike is not being rode to make sure that the valves are all closed, do this by finding the "hard" part of the stroke in your kick starter, it has seemed to help my bike's out.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now