mercury 2 stroke outboard oil mixture question

I just picked up a beautiful 93 20hp 2stroke merc that runs on a 50:1 oil mixture and i was wondering if anyone has ever ran the amsoil or any full synthetic oil at say 75 or 100:1 in a 2stroke outboard besides yamaha to run a bit cleaner.I know amsoil makes a 100:1 oil that claims you can run in any 50:1 2stroke and will run perfectly,safely and much cleaner/less carbon build up with no ill effects.I'm in no way saying i'm doing this or i will do it i just was wondering for so many yrs how a yamaha 2stroke can run safely on a 100:1 mix but no other 2stroke can.Is the yamaha built with different parts or specs? This is just a curious question.Also i know tons of people who run a 100:1 mix in their yamaha and it has lasted forever but i know some people say never to run anything less than a 50:1.I know the whole story about why they changed it yrs ago with johnson and all that good stuff but i have always been curious as to why with todays full synthetic tcw3 oil as good as it lubricates can't it be done since oil has come a long way.So my question is i guess is there anyone running a bit leaner then advertised to keep the carbon down?

Also this is not meant to begin an oil war, i just want to know if anyone has or is doing this with great results/less carbon build up and no ill effects.

the oil still has to go through the combustion process, so it still ends up in the same places....have seen many motors, some of the owners all said that they ran synthetic religiously. I could tell no difference in the exhaust ports, tuner, or leg, they looked the same as the motors that used $2/quart oil.

pappy might be able to shed a little more light on it, as he's seen a lot more 2 stroke motors than I have, and a ton more merc's and Johnny's than I ever thought about.

This could be a really long answer but I will try and keep it short.
Amsoil is not a certified oil. Never has been and never will be. They have a great marketing dept. but read the fine print about what it would take to make a warranty claim against them for a failure and you will have one of those "Aha" moments.
Running 100:1 ratios is not new. Johnson/Evinrude Marketing dept. pushed it and did it back around 1985. What was found is that during periods of non-running there wasn't enough of a film of protection on the ferrous surfaces to keep the engine protected. They wisely went back to a 50:1 mixture. We also tried full synthetics in the European race engines and found that during off-season the synthetics would not stay on the cylinder walls. The engines were all stuck and had to be dis-assembled prior to the next racing season.
The Yamaha is not made of any exotic materials compared to Johnson/Evinrude/Mercury and the rest of the players. They still have steel rods, crank, cast cylinders, steel bearings, etc. All of which will be subject to rust and corrosion depending on the level of protection you choose to leave on them. The simple cycling of cold to hot produces moisture on a daily basis inside an engine.
Secondly, and most important. In order to run a lean oil ratio everything must remain in perfect working order. Think about this for a minute. A perfect engine. No stuck rings or glazed cylinder walls or a myriad of other normal wear issues. At a 100:1 ratio there will be almost zero protection of a piston should you hit an ice bag (or whatever scenario you choose) and overheat your engine compared to running a richer ratio. Slight restriction in a high speed jet or poor fuel?....same scenario. Heavy price to pay. This is the part that I could go on and on about what the inside of an engine looks like with normal wear vs ...........
Every manufacturer, in the Owners Manual, specified running extra oil in a racing situation. What is a racing situation? Running at WOT for a 3-lap race or a Marathon. Equivalent to you running a few minutes at WOT except you are not turning left and don't have a number on the side of your boat.
Outboards don't contribute much as far as pollution goes. At the peak of boating (around 1980) it was calculated that off-road engines in total burned less than 1/10 of 1% of all gasoline burned in the US. Outboard engines are just a small part of that segment.

I totally understand what your saying.So say if you split the difference and ran a 75:1 which is much more lubrication then 100:1,do you still think your playing with fire that way or would there be enough protection?Also do you in your opinion think that full synthetic 2stroke oil is superior to reg oil.I know that reg oil does the job just fine including the $12 walmart oil but is their any advantage to it of is it just sucking money out of our wallets?I run a ton of wot so i don't know if that would come into play with your opinion.I only idle out of the channel and in no wake zones,the rest is wot,pedal to the metal,lol.

I bought a water cooled Montesa 315R trials bike from a guy that ran the Amsoil at 100:1. I took it straight to Moab Utah. On its first long trail ride up a mountain it had a chance to get the pipe and everthing warmed up real good. Once the temp came up and the built up Amsoil started to burn. It looked like the whole mountain was on fire. That thing belched smoke like a freight train for 1/2 hour. It was so bad we were worried about somebody in the distance calling the fire department. Best we could explain was that Amsoil did not burn well and coated everything including the pipe with oil. Once it started to burn it would not stop. It was fine after that and I switched to castor oil. My other experience was with with Royal purple. I was researching oil and got a hold of their oil lab. They would not certify their oil like Pappy referred to either. Why not? Everybody else does ensuring they at least meet some type of standard. Stick with oil from companies that care enough to prove it's doing what it's supposed to do by certifying it.

Sounds like you need to go back and re-read my earlier post. Both of your questions were covered in there.
Based on what you are telling me I would run a minimum of 50:1 in that engine. I would not spend the extra money on synthetic, just buy a good quality oil.
Oil's cheap......powerheads aren't!

He will be fine as long as he stops every 20 minutes and shakes the gas can. Outboard synthetics do not stay suspended in the fuel. Put the stuff in the bottom of a clear jug and see how hard you have to shake it just to mix it. Let it sit overnight and it will be back on the bottom. The modern outboard synthetics are sold to be injected not mixed. For those that use it then shake it. Read the bottles and pick the ones that say for use in premix applications. I did not read that anywhere on the last bottle of synthetic outboard lube I looked at and for good reason.

Pappy said:

.... <<snip>>....
Oil's cheap......powerheads aren't!

Click to expand...

Straight-up, that is for sure!



Never understood the desire to run lean on oil. Can't get that purdy smell if you do that. :LOL2:

I have used 100% full synthetic pennzoil for many yrs with no issues.It is for premix or direct injection as states on the bottle and certified.As far as certified i can't answer that question but i do know that millions of people use amsoil and royal purple and have great success with it including me.I just think synthetic runs cleaner that's why i use it and lubricates better.That is imo.It may be over priced and over rated but it makes me feel better to use it i guess.I will continue to run a 50:1 mix because it's better to run a hair rich then a hair lean.

2 quick questions to,i just replaced the plugs on the outboard and ran it at idle for like 10 minutes.How long would it take to for the plugs to show whether i'm running to lean or rich because the plugs were still silver and clean after only 10 mins of idle time.I have not run it on a boat yet or anything just at idle with the new plugs.I do know when reved up it sounds good and runs good,smokes like it should and has some black carbon goo coming from the prop which i know is oil and fuel that is unburned.It has not been ran for a long while and needs a good running to clean it out.I did a decarb on it already.The compression is perfect on both cylinders and it seems to run great,idles great so i would think it's running right.Any thoughts on this.

2nd when it runs at idle it runs really cool to the touch,in other words the power head is not hot at all,the water pees great and is cool to the touch,is this normal also for this outboard?It is cool out here in fl still so i figured that was it.May take a while to warm up.The stream never gets hot at all in idle.The power head like i said is extremely cool to the touch.Any thoughts on this?

Any help,thanks.

The overboard indicator is not the best for judging temperature of an engine.
Any engine that is thermostatically controlled should run at that designed temperature at idle. You may have debris blocking the vernatherm from fully seating. Just a guess.
You will drive yourself crazy looking at two stroke plugs and trying to determine whether the engine is running rich or lean by them. You are running at several different RPMs and running on totally different circuits in the carburetor. Some circuits will run richer than others.
Your best indicator you have already answered yourself. The idle quality seems good to you and the overall running quality follows suit. If the engine was running overly rich it would be running rough. Lean it would be surging a bit....just before it stuck.

I guess I can say once the outboard ran for a few minutes it was like a bit less than luke warm at idle. I guess it may be running a hair on the rich side due to the black carbon flowing out of the propeller. Better to be running a hair rich than lean. The water pump works awesome. I'm wondering if I should fully seat the fuel/air mixture screw and reset the lean/rich setting perfect. I believe once seated it's 1 1/4 turns out then find a happy medium. I have the shop book for it,I do my own work by learning myself,I will never pay the crazy money a marina wants for simple stuff I can fix myself.

It seems to run good,all 2 strokes run a little rough but it idles well and I can rev it up without a hiccup and it seems smooth. I'm doing a bunch of work to it,after I do it all I will see how it runs after I'm done.

One thing I know for sure,it hasn't been run in a long while so it needs a good run. Needs to be run in hard for a while to clean it out.

scoobeb said:

I guess I can say once the outboard ran for a few minutes it was like a bit less than luke warm at idle. I guess it may be running a hair on the rich side due to the black carbon flowing out of the propeller. Better to be running a hair rich than lean. The water pump works awesome. I'm wondering if I should fully seat the fuel/air mixture screw and reset the lean/rich setting perfect. I believe once seated it's 1 1/4 turns out then find a happy medium. I have the shop book for it,I do my own work by learning myself,I will never pay the crazy money a marina wants for simple stuff I can fix myself.

It seems to run good,all 2 strokes run a little rough but it idles well and I can rev it up without a hiccup and it seems smooth. I'm doing a bunch of work to it,after I do it all I will see how it runs after I'm done.

Click to expand...

Since everything seems to be running well w/ this motor, I think you should change out and adjust everything you can until it's just perfect!

:LOL2: :LOL2: :LOL2:

I lightly seated the screw on the carb and backed it out to 1 1/4 turns,then i went cw in till it ran like crap which was at one turn out from lightly seated,marked it,then i went cc to near 2 full turns out from lightly seated and it started to run like crap,marked that.Then i went in the middle which was at 1 1/2 turns out from lightly seated which ran best and like a freaken sewing machine,i did push it just a hair past 1 1/2 turns to make it i mean just slighly, i mean ever so slighly on the richer side to be safe,Man i couldn't be happier i tell you by the way it runs.I of course did it in a tub in f gear and not in idle.I revved it up in n and in f gear and it was as smooth as silk,not a hiccup or hesitation to speak of.The big test will come in the water when i open it up.

I also took off the lower unit and it seems like the whole thing was recently replaced but i will take it all apart to make sure,may as well while i got it off.Man the lower unit is so simple to take off.I will post pics of it when it's completely cleaned up and all the work is done.

I just wanted to update my engine,I replaced everything except the power head and lower unit gears basically. I did new,coils,wires from coils to plugs,new plugs,I replaced even the bolts holding the coils in as well as the shell that goes over the coils. I replaced lower unit oil and gaskets and drain plugs,replaced all the gas lines and new line from thermostat to the pee hole,new thermostat and gasket by the way was my issue of it not warming up,someone just stuck the shell of the Stat in with the gasket but completely removed the whole Stat so it was never warming up and always running cold. I replaced a complete new fuel filter assembly as in hoses and all,replaced the male gas intake on the engine as well,replaced a complete water pump kit,everything, impeller, gaskets,washers, key,housing,intake tube,It's all brand new,rebuilt the entire carb,new gaskets, needle,everything but the float which was good. Set the fuel air mixture screw to factory specs. New pull cord .

I de greased the entire engine I mean spotless, what fun that was,then I re greased all the fittings and anything that moves,lol. New 6 gallon tank and line, 7 bottles of full synthetic tcw 3 oil,greased the prop and spline. I think that covers most of it,runs like a sewing machine now.This will be in my possession until i either die or decide it just eats to much gas and i'm ready to go to a 4stroke. I just can't see myself getting rid of it,it is by far one of the cleanest 20/25hp 2stroke outboards on the planet unless you pull one right out of the box,compression is 100% perfect also.I had a close friend offer me a large amount of money for it and turned it down without hesitation so that will tell you what i think of this outboard.It sat for a very long time so to me it was worth putting a hair over $200 into when now i know everything as far as maintenance is taken care of for yrs now except like the lower unit oil change every 6 months or so.All i can do is hope it lasts for a very long time which i believe it will.

Here are pics of it all done and greased up. The only other plan I have for it is to sand everything above the decals and fill in any gashes with epoxy paste and then repaint it nice. The rest of the engine looks new,let me know what u think for a near 24yr old engine,imo,i think it can't get much nicer then this and i have let alot of really nice engines slip through my fingers and have extremely regretted it to the core of my soul,this time i won't make that same mistake.This motor in amazement has the power of a 25hp even know it's a 20,i cannot believe how much power this little motor has.I am going to the lake next week and this time i'm grabbing my gps because i forgot it last time and i will post how it does on a brand new 1648 flat botton jon boat with me and with 2 in it,thanks.

You did a fantastic job on that engine!

The motor looks like new, but if you asked a question about oil mixture "per title", I missed it in there. LoL As far as I can tell, there's only one problem with that motor from my perspective, the shifter is built in to the throttle grip. I've owned one merc that had that feature and I did not like it. But that's just a personal preference thing. :mrgreen: Nice job of cleaning her up and putting it back in to service.

That engine looks nice and clean. I think a lot of the Mercury's idle air adjustment is around 1-1/2 turns even though some of the books may say 1-1/4. That extra 1/4 turn made a big difference on a 90 hp that had a lean "sneeze". On a side note, I've been running the synthetic premixed at 80:1 to 100:1 in several engines for the past 8-10 years with no issues so far. But I don't run around at WOT (I usually find the quietest/smoothest cruising speed) so that may make a difference. And I usually run the boat a couple times a week during the season as well.

One thing worth mentioning is carburetor jetting. I've seen a few 2 cycle engines destroyed due to the owner running 50:1 mix when it was designed from the get-go to run 100:1. Reason being, the oil/fuel mix goes through the jet. When you double the amount of oil, some fuel is displaced, the engine's air/fuel mix runs lean. If the fuel is questionable quality from the get-go, and this happens...under load full throttle full RPM, etc, yes it can burn a piston. I actually did it on my scooter, was originally oil injected (autolube), I ditched the injector and hose and premixed it. Noticed right away that I would have to re-jet. Thought it was odd, turned around (about 4 miles from home), started back and before I turned onto the street I live on, the engine started losing power. Just died. Pulled head, piston burned on the exhaust side, smoked it, the ring, and the plated cylinder. First time I've actually experienced it, even though I'd heard of it before I called it a bunch of trashtalk. Apparently I should've listened.

If it says run 50:1, run it at 50:1. Especially on the Mercasil engines.

Agree with previous post about not liking the shift in the throttle grip. I hated it, but again personal preference....lots of guys love it for one-handed use such as running lines or duck hunting or whatever.