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Discussion Starter · #1 ·
I have a 72 cb350 that was running okay, but not perfectly. I would get little hesitations while cruising after it had warmed up. In the process of trying to get it dialed in, I must have swapped out over 50 pairs of plugs.

After my last ride, while I was pulling out the left plug, the helicoil came out with it. I put a new one in, backing the tap out regularly and coating it in grease to catch the bits. Red RTV on the new helicoil and install seemed to go fairly smoothly. Attached a fuel line to the shop vac to clean up the area, though nothing really came up. I'm assuming the grease caught all of it.

Buttoned it all up and tried to start it. It catches with choke, then starts to die pretty quickly. Flipping choke off makes it die immediately. Working off sound, only the right side is working.

Tested compression, right side is at 150, left won't even register; literally 0. I put a teaspoon of oil into left side, jumps to 150.

That was last night. This morning, went back and tested compression again. 150 in both cylinders. So I tried putting it all back together again, but still same thing; catches for ten seconds with choke, but only right side is working.

So, a few questions:
- is this rings? The wet test says yes, but it was so sudden and unprompted.
- should the oil have drained down overnight? After leaving it, would my test this morning count as a wet test or a dry test?
- do I need to remove the engine to fix whatever is going on now?

Thanks,
John
 

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Piston rings don't just fail all of a sudden. They wear out over time, loose their tension from overheating or get broken from over-revving. I've torn down motors, with broken rings in one hole, that actually ran pretty well the only clue to the problem being idle issues. You may have dislodged a tiny bit of carbon that ended up on the valve seat, holding the valve open. Running it afterwards would clear out the carbon so the valve can seat again(compression is backup). Did you try a different plug?, checked for adequate spark?
 

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Discussion Starter · #3 ·
Thanks, Mike. This is reassuring. PO said he had the top end done, so I was hoping I wouldn't have to get that involved yet. Tested compression again, and both sides came up 150 again. I must have messed something up the first time.

Checked spark on both sides. Nice white spark. Never had a fat blue spark during the time I've owned it. Maybe something to chase in the future.

With carbon on the valve, would just kicking it over a bunch clear it up? It'd be an awful vicious circle if I need to run it to clear the carbon, but it won't run because of the carbon.

Carbs have been gone through, cleaned and synced. Fuel is in the float bowls. Compression, air, spark, fuel. Valves were set and timing was done static and with a gun just before the helicoil came out.

What would happen if a big glob of bearing grease got into the chamber? I was loading the helicoil tap with grease pretty well while I was doing it. Wasn't being sloppy, so I don't think I dropped any, but would a glob of grease mess things up?
 

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Grease is just thick petroleum(oil), it will be gone as soon as you start the engine, ditto any loose chunks of carbon.
 

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Discussion Starter · #5 ·
Left it off and kicked it over for umpteen minutes. Turned it on and used the starter until it caught. Played with choke and throttle to keep it going. Once I was able to roll on the throttle a bit, it all seemed to clear up. Idling nicely at 1200. Everything seems good.

Sorry for the false alarm, and thanks for the input, Mike.
 
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