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Project RMZ 250 2009 engine running rough

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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.

$(KGrHqVHJBEFBbbnMVUVBRCWIUeHPg~~60_35.J

 

Video of the motor running - 

 

 

 

What should be my next step? 

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Your next step is build the whole motor again. All new bearings, seals, gaskets, clutch, if not a new rod at least a new piston. While the heads off pour gas in the manifolds. If the valves leak, fix it. If it doesn't, leave it. 

Your motor sounds beat up. Give it $500 and proper torque specs.

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On 26/08/2017 at 3:17 AM, notoriousE-R-I-C said:

Your next step is build the whole motor again. All new bearings, seals, gaskets, clutch, if not a new rod at least a new piston. While the heads off pour gas in the manifolds. If the valves leak, fix it. If it doesn't, leave it. 

Your motor sounds beat up. Give it $500 and proper torque specs.

 

It's so frustrating to be told to rebuild a whole motor when everything points to the motor being OK except the terrible noise! It starts very well (even when hot) and the power seems to be there it just doesn't sound healthy when running..

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What it sounds like is a whole other reason for a open up...If the motor sounded like butter, Id still open it up and attend to that horrific sounding patched up oil leak at the BOTTOM of the motor. And if I was opening the motor, Id definitely replaced all the bearings, gaskets and seals. 

i might just scotch brite pad scrub the cylinder and get new rings IF the professional I brought it to to measure said it was good. Id reuse the piston. MAYYYYbe a cylinder hone. Definitely new rings. 

test rod for play. Then make that decision.

valves, pour gas in when the heads off. If it leaks, fix it. If not. Dont touch it.

new cam chain

new clutch

bearings

gaskets/seals

thats less than $500.

Measure EVerything. Inspect EVerything 

your motor sounds no bueno, Id want it bueno. Ride it bad, it gets worse.

rebuild it, you wont worry. Confidence is good to have on a bike

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