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Cx650 smoking at mid throttle once warm

544 Views 14 Replies 7 Participants Last post by  Sidecar Bob
Hi All. Some general consensus advice would be appreciated. Just rebuilt a basket case 650ED Eurosport. Just passed her UK MOT and no issues at all. Other than I have noticed that once fully warm she puffs out grey smoke after 5k rpm which smells acrid enough to be burning oil. Not noticed oil level dropping but only done about 30mlies on her. It is a donor motor that had sit about for a bunch of years that has been fully stripped and rebuilt except crank and pistons but all other parts have been out and replaced, cleaned, bypassed, etc. Only thing I did not do was pull the heads and pistons as she had good compressions and ran ok on the bench.
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Carbs have been fully ultrasonic cleaned and fully rebuilt. All jets and emulsion tubes are new only original part is main needle as they are often not good in rebuild kits to my view. No smoke at idle and low speed and she starts and runs sweet as a nut every time and drives just fine with good power. Compressions are both 170. To my view it鈥檚 an oil control ring problem and I have a set of new standard rings to hand as I am just that sort of obsessive!馃槼. Would the populous agree she needs a re ring or am I missing something obvious and going for the nuclear option? All opinions and experience appreciated.l
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If it's been off of the road for an extended period ride it for a few hundred miles and it may improve.

650s tend to have their oil rings go slack so 170 PSI compression while blowing oil smoke isn't entirely unusual. The rings may or may not need replacing.
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The rings would be the most likely cause but it is also possible it is a head gasket.

If the air filter is restricted it will pull more oil into the combustion chambers. If it is pumping oil to the airbox it will oil its filter. Check the filter and airbox for oil.
The dipstick goes in at an angle. The top will show a lower reading than the underside. Assuming that you put it in parallel to the ground.

If you read the top you will have more oil, the underside less.

I read the underside and leave a couple of mm between the oil and the full line.

My bikes are 500s but what I've found on a number of them is that the oil level will often drop to this point and remain there, dropping no further.
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