Fatal mistake

[KarlTX]

So I did something very stupid yesterday. I forgot to add oil when I took my 2 stroke Yamaha 8HP out on the lake.

I had 1+/- gallon of fuel (pre mixed already) left in the tank and I added 1.9 gallons of straight gas. I usually mixed it at the pump but I was in a hurry and I didn't do it. The fuel hose had also pre mixed fuel in it. I ran the motor for about 8-10min at varying RPM before my passenger asked if I mixed the gas... I do run little richer than 100:1, maybe 80:1/90:1.

I immediately added oil as we were next to the shore.
The motor ran great all day after that incident, I actually used 6 gallons of gas yesterday, motor kept starting on first pull every time, ran at WOT for hours on end.

How bad is the situation? Are my cylinder walls scuffed? I'm thinking the fuel line saved my a$$... worse case scenario my fuel mix was somewhere between 250:1 to 300:1

I'm going to the store soon the get compression check tool and see where I'm standing.

[Allye]

If the compression is fine I wouldn’t worry. My lifeboat technician at work has claimed we could run a complete bladder of non oil’d fuel through our outboards and they’d be fine.

[beamishken]

If it didnt seize then your fine dont worry about it
I wouldnt even compression test it if it runs and starts ok just use it and enjoy

[KarlTX]

Well, I just tested both cylinders guys and they are reading dead even 110PSI

[KarlTX]

Originally Posted by beamishken

If it didnt seize then your fine dont worry about it
I wouldnt even compression test it if it runs and starts ok just use it and enjoy

it cost me $40 to find that out

[phantom 19]

Originally Posted by Allye

If the compression is fine I wouldn’t worry. My lifeboat technician at work has claimed we could run a complete bladder of non oil’d fuel through our outboards and they’d be fine.

I’d like to see him prove that. I’ve seen plenty of destroyed outboards run with far less fuel than that.

[Davie]

Originally Posted by phantom 19

I’d like to see him prove that. I’ve seen plenty of destroyed outboards run with far less fuel than that.

Me thinks it was oil injected!

[KarlTX]

So I opened the exhaust plate just to take a peek inside. There is some very minor scoring, probably normal for 16 year old motor. Cylinder walls have still visible honing

Now, is the discoloration (brown/black) near the top edge of the lower piston normal? Is it caused by hot gases? Top one is the same

I rechecked the compression, top cylinder is at 108 PSI and bottom is at 110PSI, cold motor.

[Locozodiac]

Don't expect to find a mint clean internal combustion chamber on 2 strokes motors specially if are pre-mix ones.

If wanting a cleaner look spray an overdose of carbon guard products say OMC, CRC Power Tuner through the carb throats with removed air silencer while the motor runs geared at fast idle, follow can instructions to the letter.

When finished, perfom a wot run for some minutes as if stealing the combo to clear/burn product's leftovers. Will not remove 100% the carbon layers already built there, but motor will run more smoothly than before.

Happy Boating

[Last Tango]

Originally Posted by KarlTX

So I opened the exhaust plate just to take a peek inside. There is some very minor scoring, probably normal for 16 year old motor. Cylinder walls have still visible honing

Now, is the discoloration (brown/black) near the top edge of the lower piston normal? Is it caused by hot gases? Top one is the same

I rechecked the compression, top cylinder is at 108 PSI and bottom is at 110PSI, cold motor.

Bit of paranoia setting in here.
If it ain't broke, don't fix it.

[beamishken]

Originally Posted by Last Tango

Bit of paranoia setting in here.
If it ain't broke, don't fix it.

Exactly

[Seaflyer02]

Originally Posted by Last Tango

Bit of paranoia setting in here.
If it ain't broke, don't fix it.

or "It ain't broke,
so I'll fix it till it is"

[KarlTX]

Originally Posted by Last Tango

Bit of paranoia setting in here.
If it ain't broke, don't fix it.

Yes, yes... I have put around $500 in to that motor ( new cowling and brand new carb) so I’m bit paranoid.

I have ran her for over 2 hours and didn’t skip a beat. Started on first pull

So like everyone has said, I will just enjoy it and stop worrying!

[Daibheid]

Most people run those older Yamaha 100:1 engines at 50:1 and have done since the Nineties as they didn’t seem to last at 100:1, not on bigger horsepowers anyway. I run my little 2hp at 50:1 despite the sticker on it saying 100:1. Modern oils are very clean so you don’t oil plugs.

[paintman]

Originally Posted by Daibheid

I run my little 2hp at 50:1 despite the sticker on it saying 100:1.

Same with my Suzuki DT4 4hp.
Not had any issues.
The owner's handbook says 100:1 after initial break-in but goes on to say for South African & commercial models use 50:1 or 'serious damage may result'.
Read on an American site some years ago (Mastertech?) not advised to run pre-mix weaker than 50:1 despite what the maker says.

[UK952]

I did some work on an airfield in Africa - wont say which country to spare their blushes - They bought 4 Stihl chainsaws to clear some brush - they complained they were rubbish as they had only run for a few weeks! They had been putting petrol (no 2 stroke) in the fuel tank and engine oil (not two stroke) in the chain oil tank. One still had some compression so we explained the error of their ways, mixed up some 2-stroke and put some chain oil in it. It managed to finish the job and still ran surprisingly well. Not recommended but you should get away with your mistake! (but I agree with above about running 50:1)

[KarlTX]

Originally Posted by UK952

Not recommended but you should get away with your mistake! (but I agree with above about running 50:1)

I've put about 20 hours since no oil in the tank situation and the motor hasn't skipped a beat. Starts on first pull even when I let it sit for 3 weeks...