smoke on the water

[xort]

I have a 4 year old Yamaha 15hp 2 stroke and it's smoking like crazy!...A LOT
I took the carb apart and cleaned it, not much to report there.
Changed the plugs with proper 1mm gap.
The mix has always been 100:1
I took it out and ran it full throttle and it runs very well; smooth running and quick to plane. That run eliminated the smoking...for about a minute. At the dock at idle the smoke quickly came back.
At low RPMs it shakes a little bit but not significantly and I can dial that out with a minor throttle change.
Adjusting the mixture screw doesn't seem to have any effect on the smoking.
The only thing I haven't done is change the float. Would a bad float allow a massive amount of smoke?

What else?

 

[Scott Danforth]

the type of oil you are using will contribute to smoke

100:1 is a bit light on oil.

 

[robert graham]

Maybe fuel pump has ripped diaphragm causing rich fuel mixture/smoke....has fuel pump been checked or replaced?

 

[xort]

I opened the fuel pump and noticed nothing out of the ordinary.

100:1 is spec for this motor. lower would create more smoking.

 

[racerone]

What oil are you using ?------The concept of lubrication and smoking on a 2 stroke is not well understood.

 

[xort]

Tcw3

 

[racerone]

You had the carburetor apart.----What did the float needle look like ??------Is there a thermostat in your motor ?----Do you understand what happens to oil inside a 2 stroke ?-----What brand / flavor of oil are you using ?

 

[jimmbo]

You mention that adjusting the Idle Mixture Screw doesn't affect the smoke. Does it affect the Idle Quality?

 

[jerryjerry05]

The idle screw should have nothing to do with the smoke.
Neither should the fuel pump.
Your premixing and TCW-3 should be right.
The cheaper oils some seem to smoke more?
Maybe try Amsoil or the premium Penzoil oil or Yamaha oils.

Have you been working on the motor??
Does it start hard?
Motor that's hard starting or your working on it start pushes more fuel in the carb and oil builds up.

 

[xort]

Valvoline TCW3, which I was using before the smoking started. Almost always starts on the first pull, whether hot or cold.
No other work has been done to the motor.
I'm going to change out the float with a rebuild kit.

Thankz all, keep trying!!

 

[Don't Panic!]

something under the float needle valve, or a stuck choke would be my first thoughts.

 

[racerone]

What is the model # of this 4 year old 2 stroke 15 HP Yamaha ??

 

[QBhoy]

Hi. Going to state the obvious and what most will be thinking of asking...forgive me...

are you certain it’s a 2 stroke...haha. Sorry. Had to ask. Just that a 4 year old (2015) 2 stroke like this would be a rare thing. The exception is if it was purchased as a commercial motor. If it is a 2 stroke and the age is certain, it will be a commercial.

so, assuming the above is the case...and you are mixing at 100-1...I wonder if it’s an auto lube perhaps ? Does it have a oil tank under the hood or remotely and it’s still mixing it’s self ? This would explain it ?

you mention a mixture screw...if it’s a premix motor and you’re mixing 100/1...I don’t get your thinking on this ? If you mean the air fuel mix screw...that’s nothing to do with it really.

send a pic of it and under the hood.

on the off chance it’s a oil injection, it will be mixing as well as you mixing too. Also should be known that oil injection systems on Yamaha sometimes default to full flow oil if the cable is snapped. Or at least it does on the 2 stroke jet skis.

keen to help you get to the bottom of this. Might also add that a little smoke is ok really.

 

[QBhoy]

Again apologies for the following. Hard to assume that guys asking for help have loads of experience or not.

when you mix 100/1....tell me how much oil you use and into how much fuel. Just in case that’s gone wrong maybe. Very easily done. God knows we’ve all got the mix wrong a little or at least had to think real hard about it, especially when it comes to an awkward fuel amount not what you’re used to.
does it do this all the time, or just with this particular tank of fuel you are using ? Is it worth starting over with a tank of fuel and oil mix ? It shouldn’t smoke lots at all with 100-1. I have always mixed my 3 Yamaha 2 strokes at 50-1 and they don’t smoke excessively when up to temp. Even at idle.

 

[jerryjerry05]

Not all outboards use a 50-1

 

[jimmbo]

To me, the more smoke the better. TCW Oil has a wonderful Scent to it when burnt, and the smoke helps keep Mosquitoes at bay.

 

[xort]

It is definitely a 2 stroke. Simple 15hp with no mixer system. That's mostly what they sell in the Bahamas. By the book, the first tank is 50:1 and thereafter it's 100:1 and that is what I mix via one of those mix cups that gives proper ratios.

I have solved the problem. I have only used the dinghy to go from the dinghy dock to my boat on a mooring for the last year or more. So I ran it hard for 15 minutes and it cleared up temporarily. I ran it hard again and it cleared up for a bit longer. I ran it hard again today and it looks close to normal. One more good run should take care of it.

Thanks all

 

[robert graham]

Glad you solved it....must have been some oil/carbon build up in the motor somewhere.....as mentioned, a 100:1 mixture really shouldn't produce much smoke. I run 50:1 in my old C90 and it only smokes a little at first cold start, then clears out after that.....I do run the 100% synthetic oil by Sierra, but it's a bit pricey at $48/gallon...

 

[QBhoy]

Glad you solved it....must have been some oil/carbon build up in the motor somewhere.....as mentioned, a 100:1 mixture really shouldn't produce much smoke. I run 50:1 in my old C90 and it only smokes a little at first cold start, then clears out after that.....I do run the 100% synthetic oil by Sierra, but it's a bit pricey at $48/gallon...

I’d be careful with using that synthetic stuff on an older engine...or a lot of others. Haven’t looked it up, but synthetic 2 stroke usually isn’t TCW-3 rated.