Heavy Smoker

[YZ250H]

Gidday guys,

Wondering if there is an obvious reason for heavy smoking (not me the 465).  I know it is running a bit rich, but surely not that much.  What about piston / ring clearance.

It's a bit embarrassing on the start line, although if I can get the holeshot I could pump out the "Bat Smoke Screen" 

Thoughts 

[pmc57]

Even with a two stroke excessive smoke is a sign of a tired and worn engine. Although from my recollection the old DT yamaha's always seemed to smoke more than others.
Your comments are confussing but typical of many I read, "I know it's running an bit rich...." . Running rich should only refer to the air fuel mix, it should not refer to the oil to fuel ratio you are running in the bike.
If you are referring to the oil mix ratio being more than recommended, ie 20:1 compared to 30:1 then you will be actually running your engine leaner in the air to fuel ratio department (more oil in the fuel leaves less fuel molecules per air molecuels which result in a lean condition). Not good for engine component longevity particually in the hot area.
Your point about piston /ring clearence is probably more than likely the cause of the excessive smoke. Wear of the rings, piston and bore allow blow by which can cause the excessive smoking.
Have a look at most of the two strokes that seem to be in good engine condition or freshly rebuilt and are tuned right at the next meet and you'll notice once they're warmed up and going, they hardly blow any smoke, this is because the oil stays where it's suppossed to, and that's down around the bearings and the rings and pistion skirt areas, not up in the combustion chamber.
I'd suggest a top end rebuild and as long as the motor has not been modified greatly, go back to the manufacturers recommended oil / fuel mix ratio and revisit the carby jetting to make sure it's as close to standard as well.   

[All Things 414]

You may have a leaking crank seal and its sucking gearbox oil into the combustion chamber. I've also had centre gaskets split and it sucks it in that way.  :'(

[YZ250H]

Thanks guys for the advice.  I understand that the richness of mixture is probably not related to smoking, but thought I would put it in there for completeness.  I am running close to standard jetting and 25:1 mixture.  There is a blubbery spot about midrange that I have not been able to iron out.  The previous owner said the bike went well, but it has not been ridden very much by him in recent times.  When I started riding the bike I needed to replace the kickstart oil seal and the gear shift lever oil seal.  Perhaps this is a sign that the crank seals are had it as well.  Crank seals have also been offered up as a possible cause of the blubbering problem as well.  The blubbering problem came on suddenly, although was made a lot better (but not perfect) by replacing the boyesen reeds.

Motor is pretty much standard apart from being on the second OS.  I have all the jets to go back to standard, so I will probably do so as you suggest.

Sounds like a (hopefully minor) pull down is in order.  To quote 414  :'( :'(

I'll have a look at piston/rings/bore and do the crank seals.  Start with the cheapest option and work at it from there.  Hopefully that will fix it - I REALLY hope it's not sucking through the centre although the YZ's don't use a gasket just treebond grey.

[All Things 414]

the YZ's don't use a gasket just treebond grey.

Oh yeah. That's right (and I own one  )
Mine would always blubber and smoke when it's done either of the above. I've been told that because of all the additives we pour into our fuel these days, crank seals don't last very long at all. I change mine every twelve months on the 414 because they're as cheap as chips and it's a pretty easy task (on a Montie anyhow).

[YZ250H]

Good on you Rosco - That's what I'm going to go for first - $75 and we should be all good again fingers crossed.

I change mine every twelve months on the 414 because they're as cheap as chips and it's a pretty easy task (on a Montie anyhow).[/color]

Not that hard on the YZ either really.  I hope you are right as splitting cases is a pain in the arse.

Thanks for the advice lads - given me some more work on bikes to do 

[Nathan S]

If its sucking gearbox oil, you'll usually smell it in the exhaust - its a nasty, acidic smell, rather than the relatively sweet smell of 2-stroke oil.

[YZ250H]

You've sniffed it.  You've ridden it.  What say you ?

FYI smoke colour is white.  I use standard (non friction modified) engine oil - that may make a difference ??

[Nathan S]

I only sniffed the seat... no wait, I mean, um....
 

I didn't notice any nasty smells from the exhaust (the owner, on the other hand...) - bearing in mind that I'd spent 13 hours in the car with DG26 and my sinuses were badly damaged.
It doesn't seem to matter what gearbox oil you use - if its an oil that's not designed to be burned (ie: not 2-stroke oil) then it smells bad when its burnt.

The flat spot felt like jetting to me, maybe retarded ignition. In my experience (which has SFA to do with big bores), rough running/flat-spotting from dodgy crank seals is less predicatable and takes longer to come clean, than your bike.

Is gearbox oil disappearing?

[jimg1au]

yz250
the best way to tell if you are sucking gearbox oil is to drain the oil and refill with R30.start the bike and wait for the smell of the R30 burning,R30 has its own smell.if you can smell the r30 burning,new seals.i had a dt360 that was running with the crancase seal blown out it sucked heaps of gearbox oil and smoked bad.
cheers
jim

[YZ250H]

Oops forgot to mention I am already running R30 

[DR]

414, I've been told the same thing by someone who shouldn't be saying such being an employee of a large petroleum company trying to sort out the issues associated with the ethanol blend crap they're feeding us. He cannot get agricultural engines to run correctly or have any sort of sustained reliability, seals, o'rings and hoses all failing within a very short period of time. I've also heard the new fuels are hydroscopic like brake fluid and left exposed will suck in H20 clear out of the air shortening shelf life. That used to be around 6-7 years but now down to a few months if that before the contaminants mess things even more. All hear say but he does the testing and I've seen the results and I trust him.

[mike1948]

If the smoke is white, then it's sure to be gearbox oil coming in through a leaky crank seal.  I had the same problem with my Bultaco years  ago racing at Echuca.  Tons of abuse from all the riders lined up behind me!
Make sure you check your crankshaft bearings, if they are starting to go, the worn seal will be the first indication.
Mike

[Nathan S]

The hydroscopic thing is one of the great myths of ethanol blended fuels. There's even a youtube vid of some American boat guy explaining why its so bad for boat motors - some of it is entriely reasonable, some of it causes me to bang my head on the table.

The really simple version of it is that ethanol blended petrol will hold a lot more water in solution, unlike non-ethanol petrol which quickly forms drops of water in the bottom of the tank.
Its these drops that cause you dramas with rough running, etc. So ethanol's ability to hold water in solution actually helps us, rather than being the hydroscopic boogey man that everyone says it is...

There are other possible dramas with E10, including the stuff Doc talked about - I just want to kill the hydroscopy myth.

[jimg1au]

hi
the main reason not to use ethanol based fuels in boats or ultra light aircraft is it can melt some fuel lines and rubber seals,shouldnt use it in old cars as well
cheers
jim
this stuff never gose near my car, bikes or boat