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Old 03 May 2020, 10:31   #1
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Country: USA
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Fatal mistake

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.
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Old 03 May 2020, 10:48   #2
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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.
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Old 03 May 2020, 11:16   #3
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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
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Old 03 May 2020, 12:10   #4
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Well, I just tested both cylinders guys and they are reading dead even 110PSI
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Old 03 May 2020, 12:11   #5
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Quote:
Originally Posted by beamishken View Post
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
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Old 03 May 2020, 13:13   #6
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If the compression is fine I wouldnt worry. My lifeboat technician at work has claimed we could run a complete bladder of non oild fuel through our outboards and theyd be fine.

Id like to see him prove that. Ive seen plenty of destroyed outboards run with far less fuel than that.
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Old 03 May 2020, 14:46   #7
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Id like to see him prove that. Ive seen plenty of destroyed outboards run with far less fuel than that.
Me thinks it was oil injected!
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Old 04 May 2020, 17:25   #8
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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.



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Old 05 May 2020, 09:48   #9
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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
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Old 06 May 2020, 07:25   #10
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Quote:
Originally Posted by KarlTX View Post
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.
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Old 06 May 2020, 13:38   #11
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Bit of paranoia setting in here.
If it ain't broke, don't fix it.
Exactly
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Old 06 May 2020, 15:51   #12
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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"
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Old 06 May 2020, 18:51   #13
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Originally Posted by Last Tango View Post
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 Im bit paranoid.

I have ran her for over 2 hours and didnt skip a beat. Started on first pull

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