Smoking from Yamaha DT80 1982

Hey all, I have a small DT80 enduro that runs pretty well but smokes
fairly bad, especially when it is cold. I know it is a 2-stroke and that
it will smoke some, but there's a steady stream of smoke coming out the
tailpipe. The smoke looks white or grey.

Is it normal for it to smoke so much? It calms down some when it warms
up but it'll still smoke pretty bad when juiced. I switched from regular
2-stroke oil to synthetic smokeless with little effect. What else could
this be coming from?

 

You might have a leaky crankshaft oil seal on the primary drive side.
Pull off the oil filler cap and see if you get pulsations of air
pressure while the engine is idling.

If the oil seal leaks, it's going to push air into the area under the
clutch cover every time the piston goes down. When it goes up, the
engine will suck oil...

If the oil seal on the magneto side of the crankshaft leaks, you'll get
crappy running and some 2-stroke oil will get up behind the magneto.
The engine won't idle right, because it's pushing fuel/air/oil mix into
the magneto instead of pushing it up the transfer passages to be
burned...



Motorcycle shops that work on 2-strokes should have a rig to pressurize
the cylinder. It would have a pressure gauge so you can watch how bad
the leakage is.

 

Thanks for comments.

I removed the head just a few weeks ago, what should I look out for? I
cleaned the deposits on the piston and head and it has a fairly new
spark plug.

 

Unburned fuel makes *black* smoke. Water vapor makes *white* smoke.
Burning oil makes *blue* smoke...

Leave the cylinder head on and run the engine with the oil filler cap
off like I told you. if you feel pulses of air pressure coming out the
oil filler hole, you have a bad oil seal on the primary drive side of
the engine. There will *never* be any air pressure (above normal air
pressure for whatever altitude you're at) inside the clutch cover of a
2-stroke engine with good oil seals while it's running...

 

*All* two-strokes chuck unburned fuel out of the exhaust.......

 

Will do. Thanks for advice.

 

a lot of oil in your muffler will take a LONG time to burn off, so switching
to synthetic mix oil may not show immediate results

YMMV

Tim

 

Another thing that 2-strokes do is distill all the gasoline and lighter
fractions out of pre-mixed or injected oil and the oil gets realy thick
and accumulates in the bottom of the crankcase...

When you open the throttle and ride really hard, the oil thins from the
heat and fresh gasoline and it starts getting pumped out of the bottom
of the crankcase...

Then the motorcycle looks like a cropduster flying low and attracts a
lot of attention from the cops, especially if you're the only speeding
2-smoke on the road...

A few motorbikes had drain plugs in the bottom of the crankcase to let
this drain out. The Suzuki 500 Titan was one. When Suzuki built the
next generation of two strokes, they thought this accumulation of oil
in the bottom of the cases might actually be a "good thing". They
connected rubber hoses from the bottom of one crankcase to the transfer
port of an adjacent cylinder, hoping that the crankcase pressure would
recycle excess oil between cylinders...

 

This is slightly off-topic, but can I replace certain oil seals without
disassembling the engine? I'm most concerned about the clutch pushrod
oil seal, the kickstarter seal, and the output shaft oil seal. I can see
all of 'em from the outside. Are these replaceable without getting into
the guts of it?

 

Large diameter lip-type oil seals like that transmission output shaft
has usually have a stamped sheet metal part inside, the rubber is
molded over the stamped metal part. Allthat holds oil seals in the
crankcases is friction, no rubber glue is used. On a Yamaha 2-stroke
that I once owned, crankcase pumping air pressure was enough to force
the magneto end oil seal out of the crankcase half...

You will probably never find this advice in a manual:

If you *carefully* drill two small holes in the oil seals and thread
sheet
metal screws into those holes you can probably pull the seal out by
pulling on the screws with pliers, without splitting the cases...

Then the new seal can be pushed in and very gently tapped into place
with a rawhide mallet...

 

Thanx krusty! I will definitely try that...my output shaft seal is
leaking like a mofo.

Im not getting any air pulses from the oil filler hole, though. Would
"smokeless" synthetic still put out some smoke if my piston rings were worn?

 

Maybe. The function of the piston rings on a 2-stroke engine isn't oil
control, they work to hold in compression pressure. Suppose the hot
gasses of combustion do leak past the rings and get to the fuel/air/oil
mix in the crankcase. They could possibly make the "smokeless" oil that
has gathered in the bottom of the crankcase get hot enough to make a
visible vapor that wouldn't be seen if the synthetic oil was actually
being burned in the combustion chamber...

Got a barbecue or a hibachi? Take it outside, fire it up and pour a few
tablespoons of your "smokeless" synthetic oil in a old pan and heat it
up over glowing charcoal and see if it does start smoking like crazy...

Maybe the smoke is coming from a lot of that "smokeless" oil in the
bottom of your crankcase, or, as another poster said, from oil
collected in your exhaust system. The only *other* source of oil smoke
would be transmission oil leaking into the crankcase past a bad seal
or, worse than that, the sealer on the mating surface between the case
halves leaks and lets transmission oil into the crankcase. But you'd
have air pulsing into the transmission if it was a leaky seal or leaky
case halves...

 

Well, I replaced my piston rings and the bike still smokes pretty bad.
Is there anything else it could be? The smoke looks blue. Could it be
the oil injection injecting too much oil?

 

Thanx for the advice. I'll try that.

I did remove the tranny dipstick and couldn't feel any air, though.