Looking for fuel/oil mix ratio options

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Douglasdzaster

Well-known member
Joined
Sep 19, 2020
Messages
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Location
Smithville,Texas
LOCATION
Smithville, Texas
Hello again everyone, I’m sitting in the house waiting for the rain to let up. Word is we got 14” in a big part of our area in the past week. I called the marina today and was tol That sandy point I beached my boat on coming in late one night is back under water.
Its going to be nice seeing the lake full again.

I’ve been sitting here planning the finishing of my rebuilding my old boat. Even have my Garmin here with me in simulation mode learning how to use the functions I haven’t been using.
Now I went and opened the manual I found online for my 1992 2 stroke 40hp Yamaha.
The outboard originally had an oil tank and pump and mixed it’s own fuel. When I got it all that had been removed. Once I got it running I’ve been using 50:1 premix ratio.
I was going through the specs in the manual and Yamaha says the pump was supposed to be using a 200:1 ratio while idling and 100:1 ratio at wide open throttle.
Does anyone have experience with older mid size Yamaha outboards?
this could explain why it doesn’t like to be idled much and things build up pretty quick when it does. By the time I idle out of a cove it’s begging for wide open throttle which clears its throat and it runs a lot smoother.
I wish it did have that oil pump set up then I could troll with it some.

Do y’all think it’s a good idea for me to play around with the ratio I’ve been mixing a little? Say half way. Instead of 50:1 try 75:1 or just change a little 60:1?
If my guess is correct it should perform better. But I don’t want to burn it up fooling around either. On the other hand if 50:1 is to heavy I’m not exactly helping it either. I understand the pumps job to automatically change the ratio to match the motors rpms. At 200:1 while trolling isn’t much lubricant IMHO. And I wouldn’t dare mix that ratio and go out and hit WOT. I hate paddling. Especially when I’m made.
Again folks I’m sitting around waiting on the rain and thinking about tweaking the boat.
I’m going to finally rebuild the front deck in the next couple of days and sat here today and decided I wanted it bigger with storage.
Suppose to have 5 straight days off dry to get it done.
If my new Minn Kota happens to get here early that deck could end up on the back burner.
Strippers (hybrid)are schooling right now.
Let me know if I should stick to the current ratio I’m using or if y’all think I might have a little room for adjustments? I looked on line and found a section that mentioned Yamaha using this ratios starting back then.
Yall keep your lines tight. Think I’ll go do dishes and surprise my wife. She knows I hate doing that more than anything else. Besides it’ll keep me from getting in deeper sitting and planning to finish the boats lay out. Lol😂76AB09B3-3F3A-494B-BE3E-0428E29CE45A.jpeg
 
There's a whole lot of other motors that will happily idle for hours on 50:1 so that's not likely to be causing your issue.

That and the fact that no outboard has been hurt from too much lubrication should be reason enough to not fool around with leaner ratios.
 
There's a whole lot of other motors that will happily idle for hours on 50:1 so that's not likely to be causing your issue.

That and the fact that no outboard has been hurt from too much lubrication should be reason enough to not fool around with leaner ratios.
I don’t know how valid it is but after I posted this I found more information that said the carburetors on the outboards made for 100:1 mix actually have different jets. And that would cause 50:1 ratio to not burn properly at idle. When I first start mine it smokes right away for just a second then doesn’t smoke at all. I use a synthetic blend oil and it burns clean but the longer I idle it esp in gear the more it will start to smoke. I can rev it a little and it helps. When I hit wot the boat jumps out of the whole and no more smoke because it’s burning more fuel. I get where I want to be and if I sit and idle before I shut it off it’ll smoke some when I start it back up because of the unburned fuel left sitting in it.
Dont get me wrong it not smoking like a train but IMHO it’s a lot comparEd to it burning clean. I did come in late one night and my stern light I bought without thinking was just above the outboard to be legal but it had a bad blinding glare and I had a bad time trying to see. It was pitch black that night so I idled all the way for about 30 minutes and it was smoking pretty good then.
I also found an article (again I’m not calling it legit) that it’s not completely healthy to run to much oil causing a shorter life time.
I would like to find the sweet spot if there is one.
I read in all of them that Yamaha did it back then to get them in the country.
 
The last yamaha 2 stroke I had was a early 90s 8hp and it called for 100to1 and that's what it got. I only owned it about a year before it got stolen but it was a good running little motor.
Man that’s sad I hate it when people steal another man’s things. I had a gun stolen that had a lot of sentimental value stolen when I was in my 20’s and I was devastated. Then a week later I couldn’t find an Abu Garcia 5,000 that my grandfather had owned for years . He took great care of everything he ever owned. That reel was like new in a felt bag. Shiny red. I remember every word he told me about how important it was to keep it clean and out of harm’s way and it would last me a lifetime. He said because the company would always be around if a part wore out.
 
Yamaha is still in business, so call them...they will know what is right !! You might akso consider going to a full syn oil, I understand it fouls less.
I already have a browser open for them with the phone numbers sir. I’ll make sure I have my serial number handy and call them tomorrow.
I’m hoping they don’t clam up on me and just tell me I need to replace the tank and pump that was removed.
When I got the boat I found an empty green can of Trufuel 40:1 in it. There wasn’t a single filter anywhere in the fuel system. The line I replaced went straight to the fuel pump and to the carburetors.
 
I don’t know how valid it is but after I posted this I found more information that said the carburetors on the outboards made for 100:1 mix actually have different jets. And that would cause 50:1 ratio to not burn properly at idle. When I first start mine it smokes right away for just a second then doesn’t smoke at all. I use a synthetic blend oil and it burns clean but the longer I idle it esp in gear the more it will start to smoke. I can rev it a little and it helps. When I hit wot the boat jumps out of the whole and no more smoke because it’s burning more fuel. I get where I want to be and if I sit and idle before I shut it off it’ll smoke some when I start it back up because of the unburned fuel left sitting in it.
Dont get me wrong it not smoking like a train but IMHO it’s a lot comparEd to it burning clean. I did come in late one night and my stern light I bought without thinking was just above the outboard to be legal but it had a bad blinding glare and I had a bad time trying to see. It was pitch black that night so I idled all the way for about 30 minutes and it was smoking pretty good then.
I also found an article (again I’m not calling it legit) that it’s not completely healthy to run to much oil causing a shorter life time.
I would like to find the sweet spot if there is one.
I read in all of them that Yamaha did it back then to get them in the country.

You're supposed to install larger jets when you go to premix, with oil mixed in, you're now burning slightly less fuel, means a lean mixture. Very few people actually do, the main jets usually have enough margin to not cause an issue, and it's a very small change anyway.

Sounds more to me like your pilot air screws are set too rich and it's loading up. Adjustments are to be made at idle, in gear, and in the water. Lean them out a touch and see what happens.
 
The oil pump in my 1994 Mercury was bad so I changed to premix and I've been running around 80:1 to 100:1 synthetic 2 stroke with no real issues. But I never run wot so I don't think the leaner mix will cause a problem for me. I did the same thing with the 90's Johnson on my previous boat, ran it 80 or 100:1 with synthetic 2 stroke. But a properly working oil pump will give you the leaner mix at idle and richen up under throttle so it might be worth fixing.
 
I believe Mr. Giggles pretty much nailed this on the head.
75 years plus ago outboards ran on a 16:1 ratio with no thermostat to help out idle quality or rid the engine of moisture. If the fuel/air ratio was set properly they did not run rough, smoke excessively, nor did they have a spark plug issue even on that ratio. Later on most outboards ran on a 24:1 ratio. Keep in mind the oil back then was pretty much the same oil used in car engine crankcases.....not great stuff. As advances were made in lubricants, metallurgy, piston and ring designs and many other hard parts the engines were successfully changed over to 50:1ratio after a break-in of 24:1. I add this because since the early 60's was the start of fixed jets. Those same jets ran the engine properly on both a 24:1 ratio then a 50:1 ratio.
As has been said, a little extra oil has never been known to damage a 2-stroke engine. Inversely a light ratio, at the very least, may have detrimental effects on long term (winter) storage with the heating and cooling cycles promoting internal corrosion.
You will often hear "Billy Bob" and "Bubba" stating that today's oils are so much better that engines can be run on light oil mix ratios.......if it were only that simple.
 
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The oil pump in my 1994 Mercury was bad so I changed to premix and I've been running around 80:1 to 100:1 synthetic 2 stroke with no real issues. But I never run wot so I don't think the leaner mix will cause a problem for me. I did the same thing with the 90's Johnson on my previous boat, ran it 80 or 100:1 with synthetic 2 stroke. But a properly working oil pump will give you the leaner mix at idle and richen up under throttle so it might be worth fixing.
Most 90's Johnsons require 50:1 TCW3 oil if premixing. If you are idling around, it will probably be okay, but I wouldn't run it hard with 100:1, synthetic or not. A lot of bass guys, who run long distances at WOT run the big 2-strokes at 40:1 or even 32:1.

Doug,
Your description sounds like it's running a little rich at idle, and just needs a minor idle adjustment as Mr. Giggles wrote. Adjust it a little at a time, probably 1/8 turn is all it will need.

Even so, better a little smoke than burnt cylinders or damaged bearings! You may have heard the saying to never let perfection ruin a good job? Lean it out too much and you could torch your engine. Just be careful.
 
Why not fix/ replace the oil pump ?? My 1992 Merc has oil injection and it has been great ! No fuss around mixing etc. Just top off the oil reservour at each filling of my fuel tank. Idle is great, you can almost hear each cylinder fire as it puts along...no worries about running wot...just piece of mind.
 
I guess the reason to not fix the pump is when the pump stops, unless you hear the alarm, your first clue it stopped is your motor blows up. When I was running snowmobiles we never trusted those oil pumps. Always used premix. I've never had an outboard with an oil pump though, so I could be wrong.
 
You're supposed to install larger jets when you go to premix, with oil mixed in, you're now burning slightly less fuel, means a lean mixture. Very few people actually do, the main jets usually have enough margin to not cause an issue, and it's a very small change anyway.

Sounds more to me like your pilot air screws are set too rich and it's loading up. Adjustments are to be made at idle, in gear, and in the water. Lean them out a touch and see what happens.
I can sure try to tune them in a little more.
I had a hunch about the jet size. never had a chance to call Yamaha today but planning on it tom Because it’s looking like my birthday present will be here Monday and that leaves me with a couple of days I’d really like to be fishing.
 
I guess the reason to not fix the pump is when the pump stops, unless you hear the alarm, your first clue it stopped is your motor blows up. When I was running snowmobiles we never trusted those oil pumps. Always used premix. I've never had an outboard with an oil pump though, so I could be wrong.
I've never had a outboard with the pump either but have had atvs in the past with similar setups and deleting that pump and mixing the oil into the gas was a common modification. The atvs didn't have a warning alarm if it stopped working the engine locking up was the alarm.
 
I guess the reason to not fix the pump is when the pump stops, unless you hear the alarm, your first clue it stopped is your motor blows up. When I was running snowmobiles we never trusted those oil pumps. Always used premix. I've never had an outboard with an oil pump though, so I could be wrong.
Look at the number of pumps that truely fail...I wouldn't trust the VRO as their percentage was pretty high. Have researched Mercury and spoke with a few long time mechanics, the failure rate on Mercs are extremely low....I am speaking of my 1992 two stroke oil injected. I found no one with anything bad to say about them. Other models could be different...
 
The gear-driven Mercs are pretty dependable, just not as dependable as mixing the oil yourself.
 
So..it does take some time for the oil to work thru the motor..as per G.Jennings. So one has been going slow for awhile and sees foul weather coming. Your oiling ratio has been lean on oil just at the time you head home quickly. So now..for longer than ya might think..your motor is under lubed for a spell. No issue with premix.

Some motors have the piston thrust on the intake side on power stroke where things are cooler and wetter. Some have the thrust on the exhaust side where things are hotter and dryer...so figure that in.
 
By the time I got around to calling Yamaha today I missed them. Due to the time difference.
I have a ton of things to do before I go fishing and it’s eating me up. The lake I like to fish is an hour away. I called the marina to get the down low with all the rain. Water was coming back up , the big blue cat are out in deep water and they are biting. The hybrid strippers just started schooling.
In between what I’m supposed to be doing this weekend I’ll take the boat to a little bear by lake and adjust those carburetors and give it a good run.
Conditions are forecasted to be great Tuesday. My new TM and lithium ion batteries are supposed to be here Monday. Fingers crossed.
I’m calling Yamaha again first thing Monday and I’ll let y’all know what I find out.
 
When you call Yamaha keep this in mind.
You are calling customer service personnel. Customer service is as much marketing driven as it is technically driven. The company mantra will no doubt be to tell you 100:1.
When I worked for OMC both in Field service and engineering, engineering was always battling marketing. Along with "features", marketing always wanted less oil and zero break-in time thinking it may sell more engines. Engineering always fought against this.
So......take the advice you get with a grain of salt
 

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