50:1 Fuel mixture - Increase oil?

Status
Not open for further replies.
Joined
Nov 23, 2004
Messages
966
Location
Michigan
I have a 15hp 2-stroke Nissan outboard that I run hard and put away wet. I use it on a 10' zodiac (dinghy) and often have 2-3-4 people (and sometimes my black lab too!) going WOT for extended periods of time.

I read a while somewhere a while back, I wish I could recall where - that if you are running the outboard hard, you can (if you choose) increase the 2-stroke oil mixture in the gas.

Any harm if I increased the mixture to 40:1? I currently run Amsoil's HP Marine in all my marine 2-stroke equip.
 
no problem running 40:1......
we used to ski with an old 40h.p evinrude in the 1970s and we ran that poor old thing hard for hours on end, we always mixed it a little rich when we new we would be sking behind it.
 
Originally Posted By: Ramblejam
Originally Posted By: [email protected]
Any harm if I increased the mixture to 40:1?


No issue, though no need either.

Of note, Nissan actually recommends 20:1 during break-in.



Ok perfect. Thanks for the replies.
 
My old '58 Johnson 25hp twin called for 24:1 of what ever oil was used back then. In the late 60's I ran it at around 40-50:1 using those those 'new' pop top '50:1' oil cans. I have a little 'kicker' 3hp Yamaha that I mix 75:1 with the Amzoil. Do what makes you most comfortable, but I wouldn't go richer myself.
 
If you change the oil ratio I would also follow up with fuel mixture adjustment. If it runs lean the added heat may negate the added oil.
 
Two things come to mind.
Automatic oil injection systems tend to dump a lot more oil into the mix when the throttle is wide open, so maybe that means you are doing the right thing if you are hard on the engine.

Be aware that changing the oil/fuel mix will also change the fuel/air ratio. As Kawiguy454 says, adding more oil is leaning out the fuel/air ratio. I just wouldn't change it too much.
 
I read a test by a MX magazine in the 90s, that tested 5 ratios on the same engine, rebuilt and broken in 5 times with a compression pressure variance of 3psi. The carbs were jetted for the mixture, but they found more power because of less friction the closer you got to 1 to 1.
Kinda like what this guy did on the second post of this site
http://airfoolers.com/?page_id=385
I wish I could find a link to the test I read, it was set up like a white paper and was an interesting read
 
Originally Posted By: Kawiguy454
If you change the oil ratio I would also follow up with fuel mixture adjustment. If it runs lean the added heat may negate the added oil.



This is true . More oil means leaner fuel mixture.
 
Originally Posted By: Ramblejam
Originally Posted By: [email protected]
Any harm if I increased the mixture to 40:1?


No issue, though no need either.

Of note, Nissan actually recommends 20:1 during break-in.



No real need, outboards gave a lightweight load on them even at full throttle they only rev 6000...
 
Originally Posted By: Bluestream


No real need, outboards gave a lightweight load on them even at full throttle they only rev 6000...


How is wide open throttle at maximum RPM a "lightweight load" ??
 
Originally Posted By: Brad_C
Originally Posted By: Bluestream


No real need, outboards gave a lightweight load on them even at full throttle they only rev 6000...


How is wide open throttle at maximum RPM a "lightweight load" ??


Compared to a motorcycle or snowmobile at 10,000RPM its a light load. The output per CC is very low compared to other two stokes. an 800cc sled puts out 163 HP, an Evinrude V6 175HP is 2600cc
 
Last edited:
I run 32 to 1 instead of 40 to 1 in my string trimmers. They seem more powerful and I trim 3 acres for a fire break each spring.
 
Originally Posted By: Brad_C
Originally Posted By: Bluestream


No real need, outboards gave a lightweight load on them even at full throttle they only rev 6000...


How is wide open throttle at maximum RPM a "lightweight load" ??


Take your bicycle with gears (mtb for instance)....put it in first gear and go cycling (@ "WOT") on flat/level road
smile.gif
 
I have a Stihl backpack blower that I have run at 32:1 instead of the 50:1 the manual called for. It is about 12 years old and still runs fantastic with no fouling or any other problems. I have always run FD rated quality 2 cycle oils.
 
Originally Posted By: Kamele0N
Originally Posted By: Brad_C
Originally Posted By: Bluestream


No real need, outboards gave a lightweight load on them even at full throttle they only rev 6000...


How is wide open throttle at maximum RPM a "lightweight load" ??


Take your bicycle with gears (mtb for instance)....put it in first gear and go cycling (@ "WOT") on flat/level road
smile.gif



I don't think you quite understand how a propeller works, however it's not worth an argument. A properly propped boat will be running the motor at its maximum design load at full noise. That's more like your bike in first gear but up a 45 degree incline.
 
I dont think so...

When boat reaches its maximum speed (depending on prop setup) I think that engine load is aroun zero...around! Because it covers only relatively small loses of drag caused by water to sustain that speed
 
Originally Posted By: Kamele0N
I dont think so...

When boat reaches its maximum speed (depending on prop setup) I think that engine load is aroun zero...around! Because it covers only relatively small loses of drag caused by water to sustain that speed


I'd love to live in a world with your idea of physics. Unfortunately it has become apparent you have absolutely no idea what you are talking about, so I'm out.
 
pass me whatever your smoking. Boats are propped to limit rpms to a max range. That means torque, lots of it. If there was no torque at full speed, then why would the throttle need to be wide open?
 
Yep, boats are not like bikes, there is no downhill in the water so there is always load. Example:
If you have a say 20 hp outboard and you prop it so that it reaches its max rpm at full throttle pushing your specific boat, then it actually outputs 20 hp, ie the max load and power output for that engine.

But for -standard- outboards, that output and load is often moderate compared to its cyl volume and rpm.

Racing bikes, carting engines, etc are often closer to their max output that design permits, but on the other hand, they are not loaded at max for hours and hours.

Do not worry about WOTting your (standard) OPE, they are in between in load characteristics and will do perfectly well being idled and wotted all day long given that you have not set the fuel feed too lean.
 
Status
Not open for further replies.
Back
Top