Fuel and oil leaking into engine builds up when standing unless fuel tap is off?

simples to fix. ride for 15 minutes with no oil to burn the excess away then just use a quality synthetic smokeless product ( we use pj1) dont use the oil tank if it has one but pre mix it so get a plastic 5lt fuel tank and put 70ml of oil in there before putting your 5 litres of unleaded in. guarenteed smoke free
we have two scooters and 7 other two stroke bikes ( trial mx enduro) and use this method every day..

ask any of my nine bikes if thats enough.. none smoke i win events on 3 of them.. too much oil is a killer.. thick heavy oily deposits in cylinder loss of power pinking and .. smoke on start up. use a quality smoke free synthetic oil ( PJ1) and you ll be home and dry..
the smoke your having at the mo are the unburnt oil from the last time you ran the thing ie you had too much oil in the fuel as the bike is mostly on half revs or less the oil isnt all burnt off and deposits accumalate in the top of the cylineder and are burnt on start up the bike will also be running hot as it is running too lean if there is too much oil in the fuel. you ll probably find that the exhaust and top of the piston are heavily carboned. so rid ewith no oil then follow the 70.1 guide.

they both have a point which does not help you.
Either way the cause is as totalshell says and personally I would just live with it – design flaw but unlikely to break it.

I used to own a Puch 125 many years ago which did exactly the same thing if I forgot to turn off the (fuel? oil?) flow switch between rides…

I wouldn’t rule out a weeping seal or gasket allowing a bit of gearbox oil into the crankcase
It doesn’t take much oil to create a load of smoke so you wouldn’t necessarily notice the loss from the gearbox but check it anyway

i can only offer 20 years experience with competing on two stroke motorcycles as my experience and the nine that are sat in my garage which i compete on and maintain myself if you check out my blog you ll see i do everything myself

seperate oil tanks are popular in consumer bikes as they are simple and require less rider input ie oil in one hole fuel in another however specialist bikes MX trials enduro racing do not use seperate tanks thus ensureing an even mix at all times wheras a bike relying on an injector could get flooded or blocked and be starved or flooded with oil

the issue of the bike running lean if it is over oil is simple if you for any given ratio of fuel to air add oil to the mixture less fuel will be drawn in making the mixture leaner in petrol.

if you removed the cylinder head you would likely find the head and the top of the piston carboned up you may also find that the bike has a clear knock as you close the throttle especially as it returns to idle this is as a result of the carbon on the upper surface of the piston and / or the fuel been poor quality (super unleaded is a quick cure)

”Oil pumps use less oil that premix as they adjust to throttle position and revs so only put oil in when needed” exactly the principle that premix works on.

one of the first bikes i had a yamahe dt125 had the same symptoms as you describe i removed the oil pump and used premix only at 70.1 and the problem was solved. 40.1 50.1 had thier day when fuel and oil were less sophisticated than today so didnt lubricate as well.

http://pre65trials.blogspot.com/

ps dont use redex to clear it out the solvents will also clear out the oil from the bearings which is whyit is there in the first place.

totalshell – you are still wrong about the oil leaning out the air fuel mix – premix does this but pump delivery does not and pump delivery does use less oil. The pump is separate from the carb. It does not alter the air fuel ratio as it adds oil. Premixing does lean out the oil fuel ratio – you have to jet up to compensate

Do you actually have any experience of modern two stokes?

_ 35 years experience of running two-strokes 🙂 – from old stuff to modern stuff.

yes uplink – but its does not go thru the main jet so does not alter fuel metering. thats my experience anyway

TJ – indeed but the mixture in the engine is leaned up regardless

You would need to rejet if you took the pump out and used premix though

For arguments sake and to make the sums easy, if you switched to a 20:1 premix, you’d need to increase the jetting by 5%
In a perfect world, of course 🙂

Well he’s talking about using 70:1 which will only mean a change of around 1.5% in the mixture
I suspect most 2 stroke engines could easily handle that without a noticeable difference, doesn’t make it optimal though

There’s too many other things – environmentals, fuel quality etc. that affect mixture a lot more than 1.5%
So if you’re happy with 70:1 go for it

just use a proper oil. expensive is just a matter of perspective really. i woundn’t run anything other than silkolene comp2 in an injector bike and pro2 in a premix one. fancy stuff smells nice too.