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Cx650 smoking at mid throttle once warm

566 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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Thanks for the heads up. It鈥檚 just embarrassing once she is fully warm馃槈. On da Lance of probability is the oil ring the most likely cause or am I missing something simple?
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.
Too few miles to know if you have a real long term problem, keep running it for another couple of hundred and if still bad then we鈥檒l try figure it out. Could just be all sorts of ol鈥 junk it just needs to blow off.
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Thanks will do that and will also try the trans fluid and acetone trick too. Just incase it鈥檚 a stuck ring. Also when I removed the oil filler / dipstick there is a lot of pulsing pressure in harmonic with the pistons moving. Is that normal or a sign of too much blowby?
Have you checked to make sure that the crankcase breather is not obstructed in some way?
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Hi yes while engine was out I cleared it all out
It is normal.
I have been checking my own oil consumption - according to recent figures I've taken, I burn a pint every 200-250 miles.



I would just keep an eye on your consumption. All engines burn a bit of oil, for the most part anyway- modern variable valve engines (in cars for example) seem to burn a lot more oil than older engine designs I find.
I have been checking my own oil consumption - according to recent figures I've taken, I burn a pint every 200-250 miles.
Are you filling it to the upper line on the dipstick or halfway? The upper line is the maximum recommended, not the optimum level.
Some years ago something I read on another forum about how much oil should be put into an engine got me thinking. Before that I had always filled engines to the upper mark and topped them up when they reached 1/2 way down, every couple of fill-ups. I tried putting the exact amount of oil Honda specifies into my GoldWing's engine and it came exactly 1/2 way between the upper and lower marks. I decided to try running it with the oil at that level for awhile to see what happened. Miracle of miracles - its oil consumption dropped to about 1/2 litre in 6,000Km.
When I next changed the oil on the GL500 I had at the time I again put in the amount the book said and found the level about halfway between the marks so I left it there and that engine's oil consumption dropped too.
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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.
I put it in so that the threads on the dipstick are in line with the ones in the crankcase. I usually orient the stick so that the flat side is perpendicular to the axis of the bike so that the oil on it is at a bit of an angle. Surprisingly the angle is hard to notice.
That's a good point Bob, and one I am aware of and have also looked into, but in my case oil consumption from mid-way down to minimum is just as quick as maximum to half way, anyway - so may aswel make sure I am full before a full ride.

Of course, ride quality can vary, but my oil consumption on the motorway, or at any extended length of time at a speed of 50-70mph is (or at least last time I checked) at about 400 miles to that pint. Constant town/commuting destroys even that miserable consumation spectacle.
I understand. The original engine from Eccles (CX650E based sidecar machine) always consumed oil at about 1/4 litre per tank of fuel. None of the easier "fixes" (including new valve stem seals and soaking the cylinders with Seafoam) helped significantly and I didn't want to take it apart enough to replace the rings so I just lived with it and carried oil the odd time I was going far enough that I expected to need to add some.
I did find that filling it to the upper line instead of halfway didn't make a significant difference in how soon the level was at the lower line.
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