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Old January 12th, 2022, 09:27 PM   #1
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Name: Terry
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Motorcycle(s): BMW R1200GS, R1100S, Suzuki GR650, Ninja 250 Pregen

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Unhappy Reviving a Ninja 250 - Low compression - Piston rings?

Hello and thanks for this great forum. I'm trying to revive a 2006 Ninja 250 that has been sitting for at least several years. It only has 1000 miles and still has the break-in sticker on the tach, so I'm a bit stumped as to why it has so many problems. Unfortunately no history on the bike. Bought it off some guy who tried to fix it but didn't have the time or the aptitude to do more than (attempt to) clean the carbs (incorrectly and lost parts). He had got it in a trade from some other guy. Nobody has seen it run yet. I started my riding career on a Ninja 500 so it would be nostalgic to ride around on this scoot. Motorcycle is cosmetically almost a 9/10. Fairings are almost perfect and no indications of crashes. Very minimal amounts of rust in fuel tank and on frame.

Currently it won't start. I've done the following.

Rebuilt the carbs (with all the parts) and tried to start it using ether. Did not get a light off even with copious amounts of starting fluid.

Changed oil. Oil was extremely overfilled and reeked of gasoline. Realized fuel had been leaking through the diaphragm on the vacuum petcock and accumulating in the engine.

Replaced spark plugs NGK CR8HSAs. Verified good spark visually (ground spark plug against frame and cranked engine).

Adjusted valves, 3/4 valves had almost no clearance. Adjusted intakes to 0.005 and exhausts to 0.006.

Still no start. Hooked up a compression tester. Showing 60psi on cylinder 1 and 55 on 2. Uh oh.

Put a teaspoon of oil in the cylinders and cranked again. 170psi in 1 and 200 in 2. Makes me think piston rings are stuck?

Installed spark plugs and tried to start again. Bike made some popping noises and blue smoke is puffing out of the crankcase breather tube. Still won't start.

Hooked up compression tester again. Back to 60psi.

So what have I gotten myself into? Symptoms seem to point to the cylinders not sealing up properly so either valves bent, piston rings stuck, or something worse.

If it's piston rings, is there anything I can try to see if I can free them without tearing the engine apart?
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Old January 14th, 2022, 08:15 AM   #2
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I've read that a 1/2 oz of marvel mystery oil poured into each cylinder has reportedly worked wonders on long neglected engines.

Certainly worth a shot, no? I'd suggest leaving it to work for 24-48 hours prior to cranking.

Suggest a pro clean on carbs as well, wet testing for any float valve leaks. Do the petcock as well.

Brand new plugs, and new fuel after draining the old prior to start attempts. Fully charge the battery as well.
Check state of air filter as well.

Best o' luck with it.
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