2-stroke bike exhaust problem?

Question

When I start my bike every morning, I see a little bit blue-black smoke coming out. Then, I usually rev to the highest a few times, clouds of smoke is emitted. But, I ride it and go, no smoke anymore. Is it common to emit smoke just when starting? Do your bike emit blue-black smoke when starting? How can I fix the problem?

Answer 1

Cold Start on 2Strokes is a peculiar condition

Oil does NOT smoke when it's "Room temperature",,,as in a Cold Engine.

Here's what is actually happening.

Cold Start SMOKE is as much of a SHUT DOWN "problem" as it is Start-Up,,,,,that's where it begins,at Shut Down.
Even after Shut Down---and You & Bike are fast Asleep for the Night.....
The BIKE is still "doing something" that many folks dont quite realize.

2Strokes run on a Fuel:Oil Mix.
It's either Pre-Mixed with the Fuel in the gastank,
Or it's fed via an injection pump into the engine,,,and it's Mixed INTERNALLY with the Fuel.

One way or the other,,,a 2 Stroke BURNS a Fuel & Oil mix.
ALWAYS.

What happens when you shut it down----
The Internal parts of the engine are Coated with an Oil&Fuel Mist.

The FUEL component evaporates,,,leaving only the Oil.
That Oil ONLY no longer exists in any sort OIL:Fuel DILUTION RATIO.

Pretty much "Pure Oil",,,all over the inside of engine.

Then,,,over several hours time,,,any Bulk of it drains off and PUDDLES in bottom of crankcase.

So what the Bike is "DOING" itself,,,,while shutdown overnite,,,
is Greatly Multiplying the RATIO of Oil it must deal with the next time you start it.

So in the Morning,,upon Cold Start----
You have a Thick,Cold PUDDLE of Oil in a place where there should be NONE.

The only Oil in a 2 stroke Engine,,,is normally what FLOWS THROUGH in the form of a MIST.

When You Start it,,,,
You Begin Again to Flow Through with FUEL and Oil.
And,,the engine parts begin to warm up and "melt" the Cold Puddle.

Easy to see how the Correct RATIO is greatly Richened with the additional Oil.

The Fuel begins to dilute the puddle,,,Increasing the amount of oil being burned.
Parts warm up,,,melting the puddle,,,again increasing the Oil quantity which is being burned.

As you can see.....it's a PROCESS of both
SOLVENT(the Fuel),,,
and HEAT( The warm up period)

All the vagrant oil left from Last Shutdown takes a while to be diluted,,
absorbed into the actual DELIVERED Mix,,,
and finally be cleaned out.

Then at That point,,,You're back to running strictly on the CORRECT Fuel:Oil ratio being delivered to the engine.

Obviously,,,the Excess Oil being Burned intially at ColdStart will make More Smoke.

But THAT only explains PART of the cycle.

The Extra Oil is NOT fully Burned.
Neither is 100% of the Fuel.

Much of the extra oil,,,and a tiny portion of the Fuel EXIT the engine and go into the Exhaust Port and the Exhaust System.

Maybe Not Necessary to understand the concept of "Temperature Line",,except perhaps in simplest terms.

Example:
If you'd hold a metal rod a few feet long with one end in a fire,,,
It would be cool to hold for a few minutes----maybe even long enough for the Fire-End to glow red.
EVENTUALLY,,the heat would travel through the rod and become very hot at the "handle end".
Duh,,,LOL:)

And if that Rod was coated with Oil,,,Imagine what the Smoke would look like as the Rod heated enough to make the oil smoke.

Right,,,it would start smoking at Hot End,,,Only Tip of Rod would smoke.
And it would Gradually begin Smoking it's way up the Rod.
You'd have smoke from 1/4 the length,,then 1/2,,,3/4,and finally the whole length.

Engines do exact same thing.
Spark Plug/Cylinder Head,,Piston Dome heat up very soon,,,almost immediately...a few Seconds.
But it takes quite a while for Exhaust Port temp to rise,,,
and on down thru the entire exhaust system.

That ENTIRE length,,,
from Cylinder Head/Piston/Spark Plug---the engine's combustion chamber......
all the way out to the very end of the exhaust pipe is COATED in
COLD OIL( as well as a sort of Cooked-Down TAR and forms of charcoal created by Previous running)

Even though there's literally FIRE blowing through the engine and exhaust....it takes a While to RAISE the Temps and for it to equalize.
And as with the Example of the Rod-Held-in - Fire,,,the Temp Rise down the length is Gradual.

The Surfaces heat-up SEQUENTIALLY to a point where all the oily coating will begin to Smoke.

In effect----You see smoke from 2" down the Exhaust System ,,but NONE YET from 6"...
THEN from 6",,,then from 1 Foot down the pipe,,,then 2Ft,,and so on.

Any Oil Puddled in the Exhaust,,,,will take Longer also.

That all adds up to TIME.
From the initial Cold Oil Puddle INSIDE the engine getting cleared out,,,then the sequential Heat Rise down the Exhaust.

What we OBSERVE from the Outside with all that is a fairly long Time that Smoke exits the Exhaust when started from Cold.

How Much,and How Long,varies according to a bunch of variables.

In a very Direct way,,,a 2 Cycle Engine & It's Exhaust System have a "HIDDEN " Oil Supply to burn off,,,which feeds the Smoke Production LONG after Engine itself is Hot & Clean Enough to have quit smoking.

But it 's ENTIRELY and Absolutely a DIFFERENT CONDITION than when a 4 Cycle engine Smokes at Start Up.

A 4 Stroke can have some Oil Leak past Valve Stem Seals into combustion chamber,,and burn upon start up causing Smoke.
And a few other sources,,Crankcase Vent,etc.

That's not Technically RIGHT for it to happen---that sorta leakage SHOULDnT happen,,,,,
but it's rather Normal for many 4 stroke Engines to experience that to a minor degree.

2Cycles---are the Opposite.
They ARE "Oil Burners",,and rather Inefficient at actually Burning the Oil & consuming it during combustion.
So it's Perfectly NATURAL that they fill theirself and their exhaust systems with Oil,,,,,which WILL begin to smoke as a COLD Engine comes to Operating temps

They have a "Double Dose" of Oil to Run through Engine at Cold Start,,,and continually pour oil into their exhaust at all times they're running.

It's a dynamic series of several processes.

What can you do to STOP it???
In Theory,,,NOTHING.
"When the smoke on StartUp STOPS,,is when ya got a problem"
2 Strokes are OPPOSITE of 4 Strokes in that respect.


However,,In Practice,,,You can MINIMIZE the Natural Effect of Burning Oil and HEATING unburned Oil.

#1 Thing that yields most dramatic reduction in 2 Stroke Smoke--
Use a High Quality Synthetic Oil.
That cannot be overstressed,,,and may account for "75% of the Anti-Smoke Battle" or more.

It's more expensive than mineral oil,,,but can be mixed thinner or have any Oil Inject system's setting minimized.
That offsets the expense somewhat,,,
and improved spark plug and engine life and Fuel Mileage make Synthetics a Better Bargain in the long run.
Or at least Minimize the extra cost to negligible difference.

#2,,,On an AIR-COOLED Engine>>>REV it when it's COLD.

Not WIDE OPEN,,,but Rev it to 30~50% RPM or so.
Dont throttle it,,just hold a steady throttle.

Stone Cold from an Overnite ShutDown is THE BEST Lubrication a 2 Cycle engine gets in it's entire lifetime.
Both in terms of QUANTITY and in terms of Film Shear Strength.
An Abundance of Very Cool Oil never hurt any engine that I've ever seen or heard of.

Get it OFF choke as soon as possible.
And from a given throttle position,,as soon as engine begins to "clear up",,GRADUALLY begin reducing throttle opening.

***Water Cooled Engines---same basic procedure,,but Rev it LESS ,,,only about 20~30% of max RPM

The Principle is to Heat It as fast as possible,,,
AND to generate higher velocity of airflow thru engine.
The Bulk Flow and Higher exhaust velocity also tends to blow the excess oil further down the exhaust system initially.

A "Mechanical Procedure" for a BAD smoker is to feed it some Water.
A VERY SLIGHT Drizzle through the Carb's Intake while running at 60~75% RPM.
(!!!!! That is an operation Best left to someone knowledgeable & experienced in the procedure!!!!
It's Cheap,Quick,,and extremely effective.
But if done Done Wrong it can have Devastating results to an engine.....and it's not too difficult to Do Wrong.
A Mistake>>> WILL<<< Break Something BADLY)

Or,,,remove the exhaust system and clean it internally with any variety of chemicals suitable for the purpose.

2Stokes,,,accumulate Oil in their exhausts.
On many bikes it eventually literally drips out of the tailpipe.
Especially when cold-ish till exhaust system warms up

Most gets distilled to GUM/Tar.
Some Carbonizes to become a sort of soft coal.

Reducing/Removing that Exhaust System StockPile minimizes overall smoking,,and dramatically reduces START-UP smoke.

SOME of that "smoke" is not hardly smoke at all,,,but actually more like an OIL FOG,,,atomized?/vapourized?
ShortCycle Warm Up/Minimum useage of Choke,,and reduction of Fuel:Oil ratio minimizes that.

...........................
The whole deal about SMOKE is what has always plagued 2 Stroke Engine's general public image.

In recent years,,,it has become an environmental concern,,,and target of various legislation.
Even going so far as 2 Cycle engines being BANNED from some places.

For many good reasons besides just the Nuisance of too much smoke,,,it behooves a person to do best they can to minimize it.

Good Oil and a thorough Exhaust Cleaning probably achieves "90% " of what improvement can be made.

..........................
A few Other things---
*Old Gasoline can cause a bunch of smoke
*Improper ignition timing increases smoke
*A really Dirty air filter can increase smoke a bit
*Excessive Idling/low Speed running can increase smoke(such as from riding in stop&go or slow traffic)
*Any cause of excessively rich carb mixture makes more smoke because combustion chamber temps are lower & more carbon monoxide in exhaust gas sorta "kills the afterburn"
*Of course,,any problems or mis-adjustment in Oil Injection system can cause extra smoke

*Major Mechanical Problems----
2Strokes CAN aspirate TRANSMISSION OIL from leaking crankshaft seals(Not Tooo common,,but it happens enough),,,
or from between crankcase mating surfaces(RARE,,but it happens)
Either of those causes is usually accompanied by Poor Running characteristics,,,particularly at Idle/Low Speed.
And Invariably a LOSS of transmission oil---however slow the "leak" may be.

~~~~~~~~~~~~~~~~~~~
Yep,,Smoke is not only Common,,,,it's "Universal" even in Best-Case examples where it is almost non-existent.
It's just the nature of the beast.

"You Can't Fix what Ain't Broken."
2Strokes will always be prone to making Some smoke.

Good News is that it CAN be Minimized,,,
and usually some very simple measures help a bunch.

I'm certain I've typed WAAAAY too much to simply say
*Use Good Synthetic Oil
*Make sure it's Tuned-Up Right
*Clean the Exhaust System
*Use as Short a WarmUp as Possible

But since Yahoo don't charge by the word,,,
Here's a suggestion about SHUTDOWN Procedure that can help a bit.

Dont shutdown from Idle.
Goofy,huh??

Run it about 2 or 3,000 RPM,,,,about 1/3 Throttle for a few seconds.
Then Close the Throttle and Kill it as Simultaneously as possible.

You want 3 Conditions Met:
1--Crankshaft/Engine still spinning "FAST"
2--Throttle Closed
3--NO Spark---engine Dead

That needn't be as "Acrobatic" as it sounds,,
and I realize that folks Cannot Rev their Bike up next to their Neighbors' window at 2:00am just to shut it down.
So ya can only DO what's "Do-able"//practical to do.
And that's fine.

But here's what that shutdown drill accomplishes.
#1--Hi Speed...the Engine is pumping a LOT of air
And it's is slinging oil OFF its insides as best it can.

#2 Closed Throttle is delivering the Minimum Possible NEW Fuel:Oil mix into the Engine.
While engine is spinning Fast and Vacuuming it OUT against the Closed Carb.
It CAVITATES same as any other pump does when it's Supply is closed.
Which Minimizes Oil LEFT in engine at shutdown
#3 Dead Ignition produces NO Combustion.
Combustion,,,upon Exhaust Port opening generates a Vacuum Pulse back thru the entire intake tract to the Carb
When there's NO Spark Plug Firing,,,and Engine is Spinning DEAD,,,it draws in LESS new oil/fuel.
And,,,there's MUCH less Pressure Wave Reversion to Push the Oil/Fuel: Air Charge BACK Into the Engine.

Under Closed Throttle,,at 2,~3,000 RPM,,,Cranking Pressure is WELL under 150~175PSI.
When Exhaust Port Opens,,,its Even LESS by that time.

If Plug is Firing,,and COMBUSTION IS occurring,,,,
even with Throttle CLOSED at that speed,,,
Exhaust sees SEVERAL 100 PSI,,,a MULTIPLE of a DEAD Engine's pressure.
2Stroke "PULSE" in their exhaust,,,the LEAST thing happening in a 2Stroke is "One Way Flow" in their exhaust.

Pressure actually goes BACKWARDS--back into Engine

Imagine what happens as the Engine is trying to purge itself of final air/fuel/oil,,,,and an Exhaust Pulse slaps it in the face.
Like 2 Fans blowing at each other.
And the EXHAUST Pulse goes Alll the way back Through to the carb.

It makes the Airflow column "Drop" the Oil/Fuel.
Drops it Back into the Engine,,,where it puddles nicely overnite.

FastKill does NOT eliminate the quantity of residual oil left in the engine at Shutdown.
And the Amount of it's effect Varies a BUNCH depending upon actual engine in question.
But it DOES reduce residuals in ALL 2 cycles.

Which leaves Less Oil Hangover in the morning to deal with.

IDEAL shutdown is to Shut Off Fuel Supply on a Pre-Mix engine,,,and run it Dry at Modest RPM,,"fast idle" till it Dies.

On an Oil Injected Engine,,,as far as Reducing residual oil at shutdon,,it's Pointless to run it out of gas to kill it.
Cuz Oil Pump is Gonna Pump,regardless.
And it you do a Medium/Hi RPM RunDry Kill,,,,
It Only INCREASES Oil Pump delivery.
So ya get an engine with MORE oil in it,,,and NO gas to dilute it.
OPPOSITE of what ya Want for reducing Smoke in the Morning.

...................
Actual MODIFICATIONS to reduce smoking???
Really,,none are practical,,and any only yield marginal results.
Most possibilities are WAY outside the scope of this rant.

Increasing Compression is perhaps the only worthwhile measure.
It WILL reduce smoking....but the extent of any improvement is UNpredictable.
I cannot recommend raising compression solely for purpose of reducing smoke.
It can easily yield No worthwhile reduction.

Anything beyond that,,is off into realm of competition engines which demand max-possible/optimum lube management.
And though it generally reduces smoking,,,such results can only be considered a "side effect"

2 Strokes,,are GONNA smoke.
In vast majority of instances Good Synthetic Oil and a Clean Exhaust System are pretty much as good as you're gonna get.
Yet,,,it also almost Always give very satisfactory results & reduces the fumes to quite acceptible levels.

That ALWAYS makes a Big improvement,,,
and on SOME engines a guy can get LUCKY,,,and the results are almost Miraculous

Good Luck with it,,hope you can find anything useful in any of the above BS.

Answer 2

To warm engine-keep low varying speed until the cylinder head feels warm to the touch-then a soft run through the gears. After this is when you can b"blow it out" by revving the snot out of it-usually only something that can be done by 250cc or smaller engines with lighter flywheels.
A bit of blue smoke may indicate the crank seals sucking trans. oil...most petroleum and synthetic two stroke oils leave a whiter smoke.
A leak down test will tell.

Answer 3

You can not because it is a two stroke.

As gas and oil are fed into the cylinder for combustion AND lubrication, the heat from your engine vaporizes the mixture.

BUT when the engine is newly started, the temperature is not hot enough (yet) to do this.

Once it warms up to operating temp, the oil in the smoke (the blue tinge and the gas (the black) are fully vaporized and the engine runs clean(er).

Check your spark plug weekly ( the cold mixture tends to foul plugs so its handy to carry a spare). As the plug begins to foul it will also cause incomplete combustion.

.

Answer 4

dont worry about it unless you are running a very good sintethic oil 2 strokes will smoke. some quite abit. but when you start it do not rev to the highest it`ll distroy your engine. its not properly lubricated yet and you will wear the rings quite fast. in the morning start the bike let it sit for about 2-5 mins then dirve it normally. its better for the engine

Answer 5

It is a two stroke engine which means oil is mixed in the gas to give the piston lubrication. Two stroke means it does the job of a four stroke engine in only two revolutions of the crankshaft. It is common for a two stroke to make a little smoke upon startup. If you want,maybe changing and setting the gap on a new spark plug will reduce this somewhat.

Answer 6

Two strokes smoke when firts started. If they did not you have no oil in the fuel. When the engine warms up (heat expands rings, pistons, ect.) and burns feul effeicently it should not smoke like crazy. If it still smokes when warm I would suggest a overhaul (rering). Hope this helps ya man. Take care. Just like a car it smokes when u first start it up until the heat expands rings, guides, ect.

Answer 7

OK...here's the answer. The top end needs to be rebuilt (cylinder, piston & rings). If you cought it in time, it may just need rings. Fix it now before major engine repair is needed.
When the engine is cold, the oil in the fuel isn't getting fully burned, because of the low compression. When the engine heats up, all the parts expand, creating a tighter seal, producing greater compression, to fully burn the oil in the fuel.

Answer 8

2 stroke bikes have oil mixed in gas thats why it smokes .if it runs ok there is nothing wrong with it

Answer 9

It's pretty normal.
Don't rev it up like that either!!

The oil injector may need adjustment, but unless you know EXACTLY what you're doing, don't mess with it.

If you have to pre-mix it, it may be too rich with oil, or it could be old gas.

Answer 10

First get your silencer decarbonised. Then check your oil seals. Check your distributor shaft and see if there's an oil leak there.

White smoke is normal for a cold start on a cold morning.

Answer 11

yeah its fine its just oil from the time before but dont rev the hell out of it when its starting, that causes so much damage its not even funny, you can squeze another 20 hours from a piston by not doing that