White Smoke

[Guest]

Hi Guys,any advice on this before i tear the motor down.
850 gs with slide Mikuni Carbs
Rebuilt last year with new pistons,rings,bored oversize with honed bore.
Carbs, all new jets properly set up and balanced.
Was run in on mineral oil to specs.
All bores show 140-150 psi cold with throttle blocked open.
Replacement head less than 1000 miles on new valve stem seals.
Bike shows white smoke on acceleration and deceleration,plugs showing sooty,now using oil,but pulls like a train and starts easy....Any input appreciated......

[Larry D]

Huh ??
Mineral oil ??

[DCrippa]

Yeah I was scratching my head about that - figured he knows something I don't...

Is it possible you're not using the right motor oil? Is the jetting right could you be running lean? plugs of the right temperature? Is timing advanced?

Are you burning oil?

[trippivot]

Could you define what mineral oil to spec means.

Because when I hear mineral oil, I think of cosmetics or something household usage not high film strength engine applications.

What did you set the ring end gap and did you stager the openings 120 degrees apart not using the 12 and 6 'o clock thrust areas?

hanging/folding a oil control micro ring will do this too - if they are the three piece type. I mean the piston will go in and the top rings seal but the oil is getting thru - might have a score in there too...

look in the exhaust pipe for the excessive soot and burnt oil 1 cyl or all 4?

[tatu]

I think by mineral oil he means non synthetic.
Sounds to me like everything was done correctly, busted ring on installation?
Really easily done.

[PAULJAC47]

By mineral oil i do mean standard non synthetic as originally used in these old bikes ,always been told by engine rebuilders in uk to run engine in using this type of oil,thanks for other input here, have gapped rings,rings are in right way up,carbs have correct jets and are balanced,carbs have been,cleaned and all airways are clear,plugs of correct grade and timing spot on,using Dyna s set up ,new air filter,shims all done and valve timing correct,all four plugs are sooting still though some slightly more than others,you can actually see the motor burning rich just off idle,using a Gunson colourtune which lets you see into the combustion chamber,guess the next thing to try is to get a set of proven carbs and give them a try!!!
One thing i have noticed is some smoke apparent when you take the oil filler cap off after a run,possible crankcase pressurisation???
Any more input appreciated.....

[DCrippa]

I think by mineral oil he means non synthetic.
Sounds to me like everything was done correctly, busted ring on installation?
Really easily done.

ah semantics...

Well if you're burning oil it has to get in there somehow... +1 to this or the scored wall being the likely culprit.


Man that Gunson colortune is the bees knees! I want one now.

http://www.youtube.com/watch?v=6hFUvQ4gaPc

[kingofvenus]

Could you define what mineral oil to spec means.

Because when I hear mineral oil, I think of cosmetics or something household usage not high film strength engine applications.

What did you set the ring end gap and did you stager the openings 120 degrees apart not using the 12 and 6 'o clock thrust areas?

hanging/folding a oil control micro ring will do this too - if they are the three piece type. I mean the piston will go in and the top rings seal but the oil is getting thru - might have a score in there too...

look in the exhaust pipe for the excessive soot and burnt oil 1 cyl or all 4?

I folded over the corner on an oil ring once, put a nice sized score in a freshly bored wall. Ended up having to resleeve it....

[hampshirehog]

You won't get white smoke caused by your carbs being set up too rich - you'll get black smoke. Plus when you are running just off idle you will get a yellow flame when see through a Colourtune. If you pull, say, 2 plug leads (so that the engine revs won't scream up) and hold the throttle fixed at around 1/4 throttle you will see the blue flame come back - you have to hold it steady for a time though - not a 'blip'.

White smoke is oil smoke. You're going to have to pull the top end to see what's what I'm afraid.

[PAULJAC47]

You won't get white smoke caused by your carbs being set up too rich - you'll get black smoke. Plus when you are running just off idle you will get a yellow flame when see through a Colourtune. If you pull, say, 2 plug leads (so that the engine revs won't scream up) and hold the throttle fixed at around 1/4 throttle you will see the blue flame come back - you have to hold it steady for a time though - not a 'blip'.

White smoke is oil smoke. You're going to have to pull the top end to see what's what I'm afraid.

Thanks for that Hog,why do you get the Blue flame back when running on two?and yellow just off idle.According to the colourtune bumf,you should get blue right through the range with a gradual throttle increase,and initially blue then yellow,then blue if you snap throttle open