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Author Topic:   Oil Gas Ratio
Bubba posted 12-06-2001 07:40 PM ET (US)   Profile for Bubba   Send Email to Bubba  
I have used 50:1 ratio (pint of oil for six gal of gas) since purchasing my boat a few months ago on the instruction from the previous owner. It's an '84 OR with a 150 Yamaha. I have since ordered a Manual for the engine and it recommends a ratio of 100:1.
I am planning to start mixing 100:1 because I do have lots of engine smoke especially on cold startup and my plugs were dark and damp when I pulled them to re-guage.
I am wondering what other '84 150 Yamaha owners mix or recommend. Also it seems this was the only year Yamaha recomends 100:1, all later year engines they recommend 50:1.
Thanks for all replys.....
JBCornwell posted 12-06-2001 09:56 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Yo, Bubba.

Yamaha (and some other manufacturers) backed off from the 100:1 recommendation pretty quickly. Check with your friendly neighborhood Yammy dealer and I expect (s)he will tell you to use 50:1.

Red sky at night. . .
JB :)

Tom W Clark posted 12-07-2001 01:18 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

I think JB is correct. Many of the manufacturers recommended a 100:1 mix in the mid 1980's because the motor were so well refined they could get away with the leaner mix. But there was a catch: While they ran fine with the 100:1 mix there was not enough oil left on the cylinder walls to protect them against rust and corrosion unless the motors were run on an almost daily basis. Since most recreational boaters only use their boats occasionally, this caused problems. The solution was simply to revert back to the 50:1 mix which had worked well for decades.

Lil Whaler Lover posted 12-07-2001 07:07 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     

I had a 15 hp Mariner years ago that was built by Yamaha. Mariner recommended a 50:1 oil mix, but Yamaha recommended a 100:1 mix for the same motor. I started checking the condition of the spark plugs and found alot of fouling and smoking at 50:1, but the ignition system was strong enough to keep it running. At 100:1 there was no smoke and the plugs were a little "hot", so I backed off gradually and wound up using about 7.5 gallons of gas to a pint of oil. No smoke, great looking plugs, and a much smoother running engine.

After all is said, my only real recommendation is to pull a plug once in a while and check its condition. That will tell you what is going on inside your motor. By the way the best time to check a plug is right after running it hard for a few minutes, then shutting it down with little of no idling. That allows you to see the plug when it is stressed the most. Dave

David Ratusnik posted 12-07-2001 08:51 AM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
Bubba- I wouldn't worry about the plugs (inexpensive), I'd worry about the cylinder walls. OMC breaks in new engines at 25:1. Stick with 50:1. My .03. David
bigz posted 12-07-2001 09:35 AM ET (US)     Profile for bigz    
The Cylmer Yamaha repair manual '84 through '89 models states for engines that aren't equipped with the oil injection system the ratio should be 100:1.

Here is the kicker, on the big engines they state that the auto injection ratio climbs to 50:1 at open throttle from an idle mix of 100:1. Why wouldn't this be the case for non-auto injected models?

If it was me to play it safe, I'd use a consistent 50:1 even though they state plainly 100:1 is what the ratio should be on all non-auto injected engines.

As David states spark plugs are cheap, so you might have to change them more frequently.

I recall OMC back in the early 80's stated 50:1 which we used in our '82 -175 Johnson. A little smoke but ran like a top.

Your call Bubba ---

Bigshot posted 12-07-2001 09:58 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
That engine should be injected and I assume was converted. When Yamaha says all non-injected engines that was only up to 30hp back then. They all ran 100:1(still do). Your injected 150 burns as lean as 150:1 at idle and 50:1 at WOT. Now if the 100:1 ratio was too lean for sitting long periods, what does 100 or 150:1 injected motor cranks look like? My Yamaha 90 runs on average 88:1 per tank so I would say if you rarely run WOT you can get away with a slightly leaner mixture but stay under 70:1 probably 60:1
Bubba posted 12-08-2001 01:16 PM ET (US)     Profile for Bubba  Send Email to Bubba     
Thanks all for the replys.
I had read that the '84 Yamaha's were bad on corrosion but I didn't link that to the oil gas ratio. Not considering that the Oil Injection system was removed I had not considered the reasons to have one. (lower mix on idle). I will stay with the 50:1 ratio and keep extra plugs on hand.
You have been a great help as always.
David Ratusnik posted 12-09-2001 07:07 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
Bubba- I had a vision over the weekend that might help with the oil to gas thing. Last summer I spend several weeks at a Marina at Port Canaveral, FLA. A marine unit was training, zodiacs, guns the whole nine yards. Nice group, I trust they are all safe. The point, they were running twin Johnson somethings on their zodiacs- out of curiosity I inquired as to the gas to oil ratio. Answer 50:1. Good luck David

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