White Smoke Under Deceleration - Wrist Twisters
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post #1 of 11 Old 06-12-2017, 08:22 AM Thread Starter
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White Smoke Under Deceleration

Apparently a little bit of white smoke comes out of my tailpipe when under hard deceleration. I have yet to see it, but it's what a coach told me yesterday on the track. I did not do the 16k valve check, I'm at 32k now and I will be doing that one. I'm not sure if it's valve related, but my valves are probably out of spec with the way I beat the snot out of my bike. When I checked my oil it was slightly lower on the sight glass than I remember, but the sight glass has never been accurate for me anyways. Coolant is at the same level as I last remembered. Any ideas?

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post #2 of 11 Old 06-12-2017, 02:45 PM
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How long had you been riding....could have just been condensation burning off....or it could mean that there is a new pope. If it was just a little bit and you aren't losing coolant, I wouldn't worry about it.

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post #3 of 11 Old 06-12-2017, 03:38 PM Thread Starter
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This incident was apparently happening as I was decelerating from 9500 rpms in 5th gear coming into turn 1. Roughly 15 minutes into a session at this point. Just did a spirited ride on some twisties today with a bud, he said he didn't see anything. Also, my light burned out. Maybe that was the smoke...my bike has a habit of starting fires inside the light housing when the bulbs die...

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post #4 of 11 Old 06-12-2017, 09:13 PM
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I wouldn't worry about it. I rode my 919 like a bat out of hell, checked the valves at 40k miles for the first time and all were within spec.

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post #5 of 11 Old 06-13-2017, 02:27 AM
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There's no reason you can't check the valves any time you want. I guess there's a 16/32, when I had mine up for sale, someone asked about the valve check and I didn't know if it were done. I'm at mid 20's now but the bike has never given me any problem.

I don't see the relationship between white smoke on decel and valves being out of adjustment. I have heard of people putting scents into fluids to see if they can smell the results.

In your case, you can use scented fuel for a tank and see if you smell it, but I'd guess cooling somehow leaking in and getting drawn in under heavy decel.

https://www.summitracing.com/search/...type/fragrance

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post #6 of 11 Old 06-13-2017, 04:20 AM
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I'd be much more concerned if the white smoke was more a light blue colour and was oil smoke, which could be the result of oil being drawn into the combustion chamber under vacuum [high revs, closed throttle] past the rings or down the valve guides.

Did the observer say anything about a puff of smoke as you opened the throttle again?
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post #7 of 11 Old 06-13-2017, 08:59 PM
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Quote:
Originally Posted by K1w1Boy View Post
I'd be much more concerned if the white smoke was more a light blue colour and was oil smoke, which could be the result of oil being drawn into the combustion chamber under vacuum [high revs, closed throttle] past the rings or down the valve guides.

Did the observer say anything about a puff of smoke as you opened the throttle again?
If no puff, then likely not oil, which is what K1 is surely implying.

If the bike is cat converter equipped, I have to wonder if blue can get masked in colour due to further oil oxidation by the converter.

White is classic for coolant in the exhaust.
But, if no coolant is gone, it can't be coolant.
919s are not known to have coolant leaks from head gaskets, combustion chambers or exhaust ports.

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post #8 of 11 Old 06-20-2017, 03:15 PM
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Were you among other bikes when this happened? Did he see clearly it was YOU'RE bike and not someone before or after you? Could it be slight tire smoke from a locked up tire?

If you can not replicate the problem, then you can not diagnose it...

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post #9 of 11 Old 06-21-2017, 04:28 PM
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The

It is oil. Guaranteed. The cause is when the throttle is chopped at high RPM the compression rings have insufficient pressure differential to maintain an effective seal, and the high vacuum draws oil out of the crosshatch on the cylinder walls which then combusts. Trust me, I have seen that so many times while racing that I stopped noticing it.

Frankly, I would not worry about it.

Rob

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On the other hand, if it has not been done never assume it is impossible to do it.
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post #10 of 11 Old 06-21-2017, 04:36 PM Thread Starter
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I figured it was something along those lines. It was extremely hot that day and I was running the bike extremely hard with oil that was probably expired by that point. Ill have my friends keep an eye out for it, they're always looking at my tail anyways

Sent from my SM-G920P using Tapatalk

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post #11 of 11 Old 06-21-2017, 04:45 PM
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You did say at the start you thought the oil level was down a little.

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