Hello all, perhaps you thought immidiately that it might be the valve stem seals, which would be expected for a bike of that age, but perhaps it's something different. Situation: - Bike was sitting for about two and a half weeks. There was no smoke when I last drove the bike. - The bike has FCR39 slide carbs which tend to be a bit plugged when parked for longer (the nubby jet activated by the accelerator pump takes a while to let fuel through again). It's gotten a bit difficult to get non-ethanol fuel over here. - bike was parked close to a wall and the hand pump of the clutch was pressed in slightly (But I can't imagine any way the hydraulic fluid got into the cylinders..) - After starting the bike (took three attempts until it idled) there was white-ish smoke coming from both exhausts which took about five minutes of driving to clear up, it also sputtered a bit. My guess would be too much fuel with the spark plugs taking a while to clear up again, but the white-ish smoke had me puzzled. Any hints and tips would be greatly appreciated.
Stem seals would be blueish, due to oil burn. Sounds like you may be on the right track, the only other thing i can think of which is white is water when it's burnt
as above, if your ambient temperatures are extreme, plus possibly bike cooling down prior to three weeks if followed by "extreme" cold, then heavy condensation in sump and engine internals generally could do this, but further thought makes me wonder if you are dumping fuel in sump via leaking carb needle valves without realising it's happening? Quickest check might be to look at sump oil level as might be higher than usual plus ethanol fuel (if that's what you have in tank) will draw water/condensation more than non-ethanol. Only "hunches" but all worth exploring.
Thank you for your hints! The oil level didn't change, it also doesn't smell of fuel. The carburators had some parts replaced one year ago and should be fine, I hope there a no gunky deposits (carbs were run dry before winter storage). Temperature ist relatively stable, between 7°C in winter and 25°C in summer (garage below building), quick temperature drops don't happen there. Condensation might be a thing so I'll keep an eye on that - the white-ish smoke combined with air cooling seemed odd.
would agree condensation would be the cause as the exhaust cools when engine is stopped it draws cooler air in and the ambient air condensates in the warmer exhaust environment when engine is started the condensated moisture warms up and turns to water vapour (steam) and evaporates as the engine and exhaust heat up
White exhaust 'smoke' from an air-cooled engine can only really be water vapour from heating up condensate or, with a completely cold engine/exhaust, from the water that is one of the constituents of IC exhaust gas. When all is hot, any water will be steam and thus invisible. Apologies - hangover impeding clarity this morning!
So, drove the thing again today. Started up okay, a few small *pops* from the airbox while warming up. Before starting the engine I shook the bike a few times from side to side to "mix" the fuel a bit, in case there was water at the bottom (I'm still on the first tank of the year and with the 5% Ethanol fuel, there might be a bit of water in it). The viewing glass for the oil level wasn't looking creamy/white before starting, so the oil should be free of water. Drove great after warming up, so everything seems fine again. Solution, porbably: I should ride more.
