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Discussion Starter #1
Hello everyone. I finally got my CB200 back from its purchased state to nearly operational, but am having trouble with the left cylinder. I hope someone can help.

It was running very rough and bluish smoky at higher revs and thick greyish smoke would drift out of the exhaust muffler on turning off the bike. It kind of looked like there was a fire still burning in the cylinder. I corrected the timing which made the bike run well with no smoke...Except the right cylinder was popping a bit. So I checked and corrected the tappet gaps, which seemed to solve the slight backfire, but also cased the left cylinder to stop firing all together. This was very puzzling as I changed nothing else. Anyway after much tinkering I ended up swapping the spark plugs over which got the left firing BUT I am now back to where i started. Right cylinder ok but left running but smokey at high revs and smoke drifting out of the exhaust pipe when switched off.

Here’s the even more weird part - if I pull the high tension lead off the left plug and just touch the rubber insulation on the top of the plug it seems to run better!! This can’t be right, but it certainly seems that way.

I have rebuilt the carbs but probably not done a great cleaning job on them. So that is on the list, but could someone give me a pointer on the bluish smoke.
 

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That plug is fouled, time for new ones.
 

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Discussion Starter #3
That plug is fouled, time for new ones.
Thanks - that was my thought too. So I have ordered new plugs and will report back when fitted. I am still a bit concerned about the smoke in the exhaust and puzzled by that odd behaviour when I touched the plug connector insulation onto the top of the plug. I am wondering about buying a new ignition coil too, but it’d be nice to understand what is going on (so I know for next time). Any ideas much appreciated?
 

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The coil is fine, Pulling the cap up off the plug creates a gap that forces the coil to build up more voltage until it will fire through the mess on the end of the plug. Could be gas/oil buildup inside the mufflers from trying to start it. Run it for 20 miles or so to clear out the mufflers and see if it still smokes
 

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Discussion Starter #5
Ok thanks Mike, much appreciated. I’ll give it a try. I may have this wrong on the plug but I meant I pull the connector off on the left plug completely and hold it away, the cylinder stops as you would expect then I touch the rubber on the top of the plug and the engine revs up! Why would it make any difference if it was completely disconnected the rubber was touching (but not the metal).
Compression is a bit low - I am not 100% convinced my tester is accurate it reads 70 on both cylinders BUT the right one runs fine which I wouldn’t have thought it would if the compression was actually that low.
the other thing I noticed (I tested compression with my thumb over the plug hole) is that ther is a lot of sooty muck in the left cylinder
 

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Make sure the valves are adjusted correctly change oil and put a few miles on it, the compression numbers will get better.
 

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So quick update. I looked into the left cylinder through the spark plug hole and it was pretty black so I ran seafoam through that cylinder. That made not much difference although I think there is a little less bluish smoke, but that could be optimism playing tricks on me! I then changed the plugs as we talked about. To start with that seemed to solve the problem, then the bluish smoke gradually came back.

then I noticed that the left exhaust pipe has a wet black deposit in it vs the right which is dry. This is making me think the problem is what I originally feared - oil getting into the combustion chamber (anyone got a view on this?) Since there is no smoke in the right cylinder and the compression test shows same compression in both cylinders I am thinking not burned valves, maybe worn rings but probably worn valve guides on the left cylinder (anyone got a view on this?) so my next plan is to put some stop smoke additive in the oil (anyone got a view on this??) - I am going to try Wynn’s stop smoke.

many thoughts much appreciated.

thanks
Tom
 

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Discussion Starter #8
Another update - good news this time. I realised the carb float distance was well over 21mm. Whoops. So I reset and low and behold the blue smoke issue improved significantly. To be fai I had put wynns stop smoke in previously but had run it and observed some improvement after putting it in. Then the carb started leaking so I checked the carb and put it back together to find much reduced blue smoke (much to my surprise). The only thing now is smoke coming out of the crank case vent at high revs. Any thoughts on this...it is becoming a game of whack a mole!!
 
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