rmz 250 2009 engine help

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8/25/2017 12:58 PM

I bought a RMZ 250 2009 non-runner as a project to learn more about 4 strokes and how they work, I have been riding 2 strokes for a few years now and have completely rebuilt a fair few, I am confident with a 2 stroke motor however 4 stroke is a different story! 

The story behind the bike:

Guy took it in part exchange, the guy rode it in the street to prove it works and once he left it never started again.

Once I got it home I noticed it had lots of sealant under the engine where the 2 cases meet (assuming it is leaking oil). When the bike is kicked I could feel a lot of air coming out of the top gasket (black seal between rocker cover and head). I replaced the seal which fixed that problem.

When fixing the above problem I also checked valve clearances and all were within spec except one inlet was 0.001 out, I left it as it was.

Next up was the carb, all of the adjusters (aftermarket easy adjuster knob things) seemed so off. I think the fuel screw was about 4-5 turns out, no wonder it didn't start! It felt like someone had just been turning them hoping it did something. I reset both adjusters I could see to 2 turns out.

Next up I pulled off the carb manifold and it came off in 2 pieces! It was held together with some tape, I replaced this and it fired up!

So here I am, the bike now fires however absolutely nothing about the bike sounds right. I needed to turn the idle screw quite high to start it (could need fuel screw adjustment?) however once started I can turn it down and it will idle OK. I can ride it around my field however it gets really hot really fast and I haven't rode it for longer than 1-2 minutes as it feels like it is about to blow up on me.

The only thing I noticed is that the timing chain feels a lot more tensioned now I have put it back together compared to how it was when I first opened it up, is it possible I messed something up? I believe the tensioner is an automatic one, pic below of how it looks.


Video of the motor running - 


What should be my next step? 

8/26/2017 8:14 AM

Those cam chains when they are in place with the adjuster in are usually pretty tight so I wouldn't worry about that too much. When you reinstalled it did you back it all the way off and then let it re-adjust itself once in place?

When you had the valve cover off and checked the valves did you happen to look at the valve timing and make sure it is correct? It is possible if the bike got rebuilt before it got sold that they are off a tooth on the timing that can make them run a little iffy.


8/27/2017 6:56 AM
Edited Date/Time: 8/27/2017 6:57 AM

That is a ratchet type cam chain tensioner. You have to release it and move the arm back into the body. You install the CCT then put the spring/rod in it. Otherwise it will be over tensioned. If you just bolted it back in the cam chain is at full tension and WILL break.


8/27/2017 2:58 PM

Hondas4Life3 wrote:

That is a ratchet type cam chain tensioner. You have to release it and move the arm back into the body. You install the CCT ...more



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8/27/2017 3:09 PM

Cheers for the replies guys. I re-did the tensioner and it still sounds like in the video, not exactly sure what to do next.

Valves are in spec (except one inlet is out by 0.001), everything else looks good enough and it rides and starts fine..

Any suggestions?