Smoke on Startup

Joined
Feb 22, 2010
Messages
21
Location
Washington State, Skagit County
Bike
'91 ST1100
I have an interesting thing going on with my 1991. This bike has about 80k miles on it and runs fine. A little while back it started doing something interesting which I don't understand and was wondering if anyone else has had this and what they did about it? Occasionally (like once every dozen times or so) when starting the bike from cold in the morning I get about 15 seconds of blue smoke just shortly after startup. Then it goes away and isn't seen again during other startups or normal riding. This seems to be random in occurrence and also doesn't seem to affect the oil level that I can see. I generally start the bike on a pretty level surface on the center stand and use full choke to get it going, then back it off as I can. I did try something the other day the last time it smoked on start- I turned off the engine with the kill switch right after it started smoking and restarted immediately. Presto! No smoke on the second start! This has me baffled and so I thought I would throw my bread upon the water here, so to speak :) Anyone? Thanks for your time, I appreciate your input. Samdoggy
 
Sounds like the valve stem guide seals may be passing some oil, this runs down and settles on the inlet/exhaust valve and is ingested and burns off on startup....

Unlikely to be rings if it only does it on startup....

Do you park on the mainstand?

If it is the valve seals then it is a bit of a faff to do them but if you have that mileage it is advantageous to change the cambelt at the same time as getting the heads done.... and the valve clearances of course....

Other things to check would be water pump and stuff in there with the belt... others may better advise accordingly....
 
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I have an interesting thing going on with my 1991. This bike has about 80k miles on it and runs fine. A little while back it started doing something interesting which I don't understand and was wondering if anyone else has had this and what they did about it? Occasionally (like once every dozen times or so) when starting the bike from cold in the morning I get about 15 seconds of blue smoke just shortly after startup. Then it goes away and isn't seen again during other startups or normal riding. This seems to be random in occurrence and also doesn't seem to affect the oil level that I can see. I generally start the bike on a pretty level surface on the center stand and use full choke to get it going, then back it off as I can. I did try something the other day the last time it smoked on start- I turned off the engine with the kill switch right after it started smoking and restarted immediately. Presto! No smoke on the second start! This has me baffled and so I thought I would throw my bread upon the water here, so to speak :) Anyone? Thanks for your time, I appreciate your input. Samdoggy

You found a fix !!! IF you are not using oil and the bike runs good, I wouldn't do a darn thing at this time . Just ride it until it gets worse. It may never get worse. But if it does, then it can be considered a real problem. I would guess valve guide seals or guides too, but I wouldn't do anything about this at this time.

Maybe someone else can tell us their experience with guide or seal problems.
 
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Definitely indicates worn valve guides and/or seals. The expense to repair this would be quite high - parts alone, valves, guides and seals would be a killer, let alone the labour. I'd suggest leaving it as is also and monitor your oil level often.

Can't say I have seen this problem much, even on engines with twice the mileage, so it would be interesting to know the oil history of this bike. Brand(s) used, viscosity and frequency of changes?
 
This seems to be a rare problem with the ST's, but with that being said, it's a minor problem if it just smokes on start up. As others have advised, don't worry about it until it gets much, much worse. At present, your engine is evenly worn and is comfortable with all its parts worn at the same rate. If you do a valve job on the heads, that can increase pressure on the bottom end and can cause a problem. At 80K it could possibly survive a head job, but I would not risk it just because of the minor smoking at start up.
 
Dunno if it already needs an ICU head-job... methinks 16x P/N 12209-ML0-722, seal valve stem would deal with the issue...
Rubber + heat + age and that... especially since no serious oil consumption is noted...
But to replace those the heads need to come off, otherwise you'd be unable to depress the valve coils to unlatch the cotters...
All tools and parts provided about a day's hangar-time...
 
If it was an old Triumph it would be an electrical issue.....couldn't keep the smoke in those wires for very long........I think they even used to sell replacement smoke...........:D.............just ride it.............have fun...............ff...........BTW, all the old GL1000s used to do that if you let it set on the side stand.......oil would seep past the rings on the downhill side.............
 
I have a similar issue on my 1991 ST. But I have narrowed it down to leaving the choke on to long when warming up. If I leave the choke on full choke for more than a minute then the bike blows blue smoke. If I reduce the choke to a partial position the smoke does not happen. This is a consistent thing, I can make it smoke or not. At any rate even if it is oil and you are not using any don't worry about it.

A simple test for valve seals is leaving the bike in a low gear for down hill descents, no throttle at all. If after a bit you hit the throttle and smoke comes out then most likely it is seals/guides.
 
Have to disagree with Brad on that last sentence. Throttle off deceleration will suck oil up the cylinder walls also and past the oil ring(s), if they are worn. That test is much more likely to reveal worn oil rings. The best indication of valve guide and seal wear is upon initial start up, after oil has had a chance to leak down past the guides onto the valve tops while it was sitting unused. If the smoke disappears after a few moments and is not visible again while running, it is more certainly the guides and or seals. Continuous smoking while running is very worn piston oil rings.
 
Thanks to everyone for all the great tips and advice, will monitor oil closely and ride topped off! I will try to reduce the choke at start up and see if that does anything and just keep an eye on things in general I guess. The thing that has me stumped is that it only does it once in a while, not every time like you think worn valve guides might do. In any case, the engine seems to run normally and everything else is fine and Spring is here so I will get out there and go until something else makes itself known. Appreciate the help, gentlemen :)
 
I have been tinkering with it and the smoking is definitely connected to the choke. The more I use and the longer I leave it on, the more and longer it smokes. Goes away as soon as the choke is off. What I am wondering is what causes this? Is there a hidden filter somewhere or a thing I need to clean out to make things like before, when things operated normally? Bike has about 90k on the odo. Anyone? :)
 
Is your crankcase overfilled? Sounds like you are getting an oil mist sucked into the carbs through the PCV system/crankcase breather hose. This would be accentuated with the choke on. Pop off your air filter lid and see if it is an oily mess in there.
 
Goes away as soon as the choke is off. What I am wondering is what causes this?
(Too) rich mixture (= pulled choke) on a warm engine is producing some sooth from only partially burned fuel... we're just not used to this picture anymore, as nearly all vehicles now have EFI and catalytic converters.
But the ST1100 has a "classical" engine with carburettors, an manually operated "enricher" for cold start (the choke) and no filter elements in the exhaust.

Maybe your carbs are set "too rich" to begin with, I can't tell, worsening the effects of having the choke on...
I can only set the choke to ~50% to start, then instantly back it off to like 1/4~1/8th as the engine would first start to rumble and even stall within seconds of starting to warm up.
Taking off with the choke at 1/4~1/8th is producing some "slight" smoke (but not like an M1 Abrams under full throttle ;-) ), and I'll have to set the choke to off after 500~800 yards, otherwise the engine will again start to rumble and show tendencies to stall...
I've that on both ST's, the '00 and the '94, with my settings and the premium fuel over here...
 
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I had the air cleaner cover off recently and found no oil in there, everything looked normal. The crankcase breather system is something I have not looked at as a potential source of trouble, however. I will get out the book today and see if there are any obvious things, like filters, which need servicing. Thanks for your input :)
 
(Too) rich mixture (= pulled choke) on a warm engine is producing some sooth from only partially burned fuel... we're just not used to this picture anymore, as nearly all vehicles now have EFI and catalytic converters.
But the ST1100 has a "classical" engine with carburettors, an manually operated "enricher" for cold start (the choke) and no filter elements in the exhaust.

Maybe your carbs are set "too rich" to begin with, I can't tell, worsening the effects of having the choke on...
I can only set the choke to ~50% to start, then instantly back it off to like 1/4~1/8th as the engine would first start to rumble and even stall within seconds of starting to warm up.
Taking off with the choke at 1/4~1/8th is producing some "slight" smoke (but not like an M1 Abrams under full throttle ;-) ), and I'll have to set the choke to off after 500~800 yards, otherwise the engine will again start to rumble and show tendencies to stall...
I've that on both ST's, the '00 and the '94, with my settings and the premium fuel over here...
Thanks for your input, I tend to let the bike warm up before riding and will test other choke positions for starting when cold. I usually use full choke to start and then back off to keep from over-revving while cold, leaving the setting where engine fast idles at just under 2000 rpm and then backing off the choke when the engine shows signs of being able to run at normal idle without it. It smokes when at full or nearly full choke and when left there for a bit. I am riding this morning so will try a couple new things.
 
FWIW I start on full choke and back off immediately to about half. after about 30 seconds I will be trying to back it off more,listening for a Pinking sound to indicate more choke is needed. Then increase throttle a little and then try and shut off the choke fully, then set my throttle lock at a slightly high idle 2000 RPM. After about a minute I cut the throttle to regular Idle. That's the way I warm up the engine, NO CHOKE
I believe too much choke will strip the oil off the cylinder walls and maybe the rings.
 
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