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No Compression, could use some expert advice

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03 400 and it has little or no compression, I first disconnected the manual decomp cable and adjusted the valves...still no compression.

I pulled the cover and nothing out of the ordinary, kicked it with the cover off and no compression.

I then pulled the cam and checked auto decomp "plunger and spring which looked good.

I kicked it over with the plunger out and still no compression.

so, I hooked up a leak down tester and at tdc I had only 10% leakage, but was unable to register anything with the compression tester, so that has me a little boggled...still thinking it's the auto decomp???

Q: Dose the auto decomp plunger seal the port to the cylinder?

Q: Which direction should the auto decomp assembly on the cam rotate freely.

any advice would be appreciated!!

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Is this your bike? It was fine, then the compression went away? If I don't ride my street bike for a few weeks, the valves will stick open. I just kick it and kick it and kick it. Sooner or later, the valve will seal and it starts up.

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it's a friends bike and he kicked it more then enough to get it to fire.

So, when I got it the bike just rolls thru the kick cycle, less compression then you'd feel with an 85cc 2 stroke...not normal.

I'm trying to isolate the no-compression issue...and take the auto decomp out of the picture before I decide to pull the head.

Good Idea to check the valve a little closer...I'll give them a rap with a soft hammer make sure their closing.

I would like to know how the plunger and spring function, if by removing the two dose that open a port to the cylinder where compression is lost, does the pin actually seal off that port and only open when depressed?

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The decomp pushes down one of the exhaust valves. It isn't a valve.

Make sure you are not dealing with a cracked spark plug.

Next most obvious is you adjusted the valves on the wrong stroke. They will be super tight when you try to kick it over.

Turn over the motor to the timing mark, the rocker arms will be tight. (Wrong stroke)

Turn over the motor to the timing mark, the rocker arms will be loose. (Right stroke)

(Grab the rocker arm and try to wiggle it.)

If the rocker arms are tight on both strokes, the valves are badly out of adjustment.

My bet is your valves are incorrectly adjusted. I hope I'm right as the fix is the cheapest.

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You could also put a squirt of motor oil into the plug hole, crank it over slowly (to coat the cyl walls), then check the compression. If it jumps up, points to the rings. If no change, valves.

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The decomp pushes down one of the exhaust valves. It isn't a valve.

Make sure you are not dealing with a cracked spark plug.

Next most obvious is you adjusted the valves on the wrong stroke. They will be super tight when you try to kick it over.

Turn over the motor to the timing mark, the rocker arms will be tight. (Wrong stroke)

Turn over the motor to the timing mark, the rocker arms will be loose. (Right stroke)

(Grab the rocker arm and try to wiggle it.)

If the rocker arms are tight on both strokes, the valves are badly out of adjustment.

My bet is your valves are incorrectly adjusted. I hope I'm right as the fix is the cheapest.

Thanks for that info, but...I have the valve cover off, so the rocker arms are not depression the valves open when I'm kicking it over so the manual decompression and the adjusment of the valves are not the problem.

I did place grease over the plunger hole but I was un- able to tell if it's blowing out the grease, that will require pulling the cam again...which I plan to do.

What has me confused is I get no reading with the compression tester by kicking it over...but...with the leak down tester I get a good reading less then 10%, so, I'm thinking the auto decompression is some how releasing the compression during the kick cycle.

What would help is if some one could post how the service manual recomends checking compression and if anyone know exactly how the plunger functions.

for instance, when it's depressed by the auto decomp on the cam does it open a check valve??

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You could also put a squirt of motor oil into the plug hole, crank it over slowly (to coat the cyl walls), then check the compression. If it jumps up, points to the rings. If no change, valves.

That worked with my TL125. I put a cap full of oil into the cylinder.

Compression went from 60 to 120. It even ran until the oil burned off.

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