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Discussion Starter #1
Hello Moto Forum,

I bought a 1971 sl125 with a seized engine to learn about engines and servicing them. I have previously worked on go karts and lawn mowers for fun so I'm not to familiar with the OHC setup and far from an experienced engine builder. I soaked the piston for a week but it wouldn't budge. Then, I took off the engine from the bike and removed the top end, a few light taps removed the piston from the cylinder. I decided to replace the cylinder and piston with one from a ebay with a 56.5mm bore. I removed the valves and lapped them. I assembled it all, adjusting the point gap, ignition timing, and valves using the shop manual. I have double and tripled checked these against the manual after it has not started. I am unable to start the bike. I have fuel because i'm just squirting some gas down the carb and I have what seems to be a strong spark. I'm working on borrowing a compression tester. When i kick over the engine, it seems to make a sloshing sound and I hear what sounds to be air escaping through the intake valve on the compression stroke when I kick slowly. Irregularly, the engine will make a pop and shoot a flame out of the carburetor. I am wondering what you guys think and what my course of action should be? Email or message me for a link to a video of me trying to start the bike and the spark as I can't post links yet.

Please enlighten me!:)
 

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Yes, I went through all the jets making sure they were clear and cleaned out the bowl which was not very dirty. I am not sure if that is the problem because it will not run even for a little bit when I put gas directly down the carb. Is there a test I can do to make sure the valves are seating properly?
 

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A leak down test may be something to help you determine where the leak is occurring if the compression test reveals a problem. Here are two links. one is the shade tree method, and the other is more detailed.

http://www.dansmc.com/leakdown.htm

http://www.gregsengine.com/cylinder-leakdown-testing.html

Since the engine was taken apart, it may be possible that the timing chain is off by a tooth? If that happened, would it then be possible that the intake and exhaust valves would not be completely closed at TDC? Maybe someone with more experience than me will chime in....
 

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Thanks for the reply! There is a possibility that the cam chain is off by a tooth, but I have doubled and triple checked it. Sadly, I was not able to get my hands on a compression tester but I am working on it. I may try to pop start it just for testing purposes when my gas tank comes in(it was missing one). Another piece of information is when I kick it over it seems to gurgle, but I do not have an exhaust for it so that might be a normal sound without an exhaust?
 

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Discussion Starter #8
So I got my hands on a compression tester. I got readings(on a cold engine as it doesn't start) as high as 125 psi, but the needle jumped to that and then feel quickly fell to 50 psi and then fell slowly. Does this mean the valves are leaking?
 
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