Would any one be able to give me a oil to gas ratio for a "vintage" (the oldest it could be was 1984) Mercury 7.5 hp outboard?
- Status
You can run 50:1 with most oils
Old way to run them was 40:1. Nowadays 2 stroke oil technology has improved so much that 50:1 with anything but elcheapo oil will work well. FYI-- consumer reports did a test a few years back in weed eaters calling for 50:1 showing that with name brand oils like texaco, castrol, mobile etc. you can run at 100:1 without any problems...not that I would ever try it in my motor. Nicest part about running 50:1 is that many fuel docks sell it pre-mixed. Through my trial and error, espcially in the smaller motors, I have found that the best recipe is to find a brand you like and stick with it. If you mix the same oil each time you can get the motor dialed in the way you like it and not have to wonder if your oil is the culprit if the motor is acting funny.
Old way to run them was 40:1. Nowadays 2 stroke oil technology has improved so much that 50:1 with anything but elcheapo oil will work well. FYI-- consumer reports did a test a few years back in weed eaters calling for 50:1 showing that with name brand oils like texaco, castrol, mobile etc. you can run at 100:1 without any problems...not that I would ever try it in my motor. Nicest part about running 50:1 is that many fuel docks sell it pre-mixed. Through my trial and error, espcially in the smaller motors, I have found that the best recipe is to find a brand you like and stick with it. If you mix the same oil each time you can get the motor dialed in the way you like it and not have to wonder if your oil is the culprit if the motor is acting funny.
50 to 1 is correct.
I had a trusty old 1973 Chrysler Magnum 10 hp that I used until I bought my new 4 stroke Tohatsu. Always went 50 to 1 - no more and no less. The chap who bought my antique Chrysler says it runs just great following my instructions for mixture.
I had a trusty old 1973 Chrysler Magnum 10 hp that I used until I bought my new 4 stroke Tohatsu. Always went 50 to 1 - no more and no less. The chap who bought my antique Chrysler says it runs just great following my instructions for mixture.
I had an old Evinrude years ago.
The fuel/oil mix for that was supposed to be 50:1. I used that mix and got a lot of blue smoke. When I pulled the plugs, they were fouled with unburned oil. Looking to the cylinders, I could see sludge building on the piston heads. I discussed this with the people who then made Evinrudes and they told me most 2 cycle outboards could safely run on 100:1 mixtures but that makers suggest a higher oil ratio since a lot of users don't mix it correctly. I slowly began to decrease the mixture on that motor and eventually settled on 100:1. The engine ran great, had little smoke, and the crud inside the cylinders cleared up. So, I suggest starting out with the recommended ratio and see if you get "excessive" smoke. Check your plugs and cylinders after every couple of uses. If it looks like you have unburned oil fouling things up, start a regime of slowly decreasing the oil mix until you find your engine's sweet spot.
The fuel/oil mix for that was supposed to be 50:1. I used that mix and got a lot of blue smoke. When I pulled the plugs, they were fouled with unburned oil. Looking to the cylinders, I could see sludge building on the piston heads. I discussed this with the people who then made Evinrudes and they told me most 2 cycle outboards could safely run on 100:1 mixtures but that makers suggest a higher oil ratio since a lot of users don't mix it correctly. I slowly began to decrease the mixture on that motor and eventually settled on 100:1. The engine ran great, had little smoke, and the crud inside the cylinders cleared up. So, I suggest starting out with the recommended ratio and see if you get "excessive" smoke. Check your plugs and cylinders after every couple of uses. If it looks like you have unburned oil fouling things up, start a regime of slowly decreasing the oil mix until you find your engine's sweet spot.
25:1
I have also seen testing where oil added up to about 10:1 will seal rings better and give longer life.Thatnot a lot of lube for a motor. I have had very good results running a 1972 Johnson 6HP at 25:1 for many years and no fouled plugs, but I do run wide open on the Zodiac 8.5 foot almost all the time. This is using the called for Champion plugs and Texaco oil with medium grade fuel. This was by the way done in controled lab and using a dyno.
I have also seen testing where oil added up to about 10:1 will seal rings better and give longer life.Thatnot a lot of lube for a motor. I have had very good results running a 1972 Johnson 6HP at 25:1 for many years and no fouled plugs, but I do run wide open on the Zodiac 8.5 foot almost all the time. This is using the called for Champion plugs and Texaco oil with medium grade fuel. This was by the way done in controled lab and using a dyno.
My Evinrude 4hp was running crappy
Untill I discovered from a sticker on the engine by the fuel hookup that said 100:1 now for years I always had 50:1 outboards so it seemed like this was wrong but the engine runs great with that ratio. The only pain in the A.. is having all these different cans of fuel in the shed with different ratios for the outboard,chain saw,etc..
Untill I discovered from a sticker on the engine by the fuel hookup that said 100:1 now for years I always had 50:1 outboards so it seemed like this was wrong but the engine runs great with that ratio. The only pain in the A.. is having all these different cans of fuel in the shed with different ratios for the outboard,chain saw,etc..
- Status