Synthetic oil in older motor?

[basser]

I have an Evinrude 115HP 1976 , I want to start running synthetic oil in the mix. Is this OK? Do I have to change the mix ratio if I do this? Thanks Dan

[basser]

Thanks Musky , I run Amsoil 2000 50:1 in all the dirt bikes so I figured why not in the boat. The mix for the boat calls for 40:1 ,am I alright if I go to 50:1?

[musky hunter]

I have run 100:1 amsoil in two different motors, a 1968 Mercury 50 and my current 1991 Force 120. It has never given me any problems whatsoever. But in the older merc, which has the old magneto/point style ignition, I got much better plug life on the synthetic, presumably because the leaner mixture burns cleaner. Performance in the Force seems to be near identical whether I run synthetic or natural lubricant. But that has electronic ignition and the better spark might be keeping my plugs cleaner. I also found that running Split Fire plugs made a tremendous difference in both motors, particularly in starting and smoother running at slower speeds. If it were my outboard, I would not hesitate to use Amsoil. I have no experience with the other brands.

[musky hunter]

The big advantage of going to 100:1 is that I found the motors ran smoother due to a more volatile gas mixture. If you run synthetic, run it at 100:1. It's designed for that thin of a ratio. If you're woried about whether or not it will work, try it at 75:1, then gradually thin it out until you are at 100:1. The thinner synthetic mixture will help you keep a hotter and less fouled plug and still be well lubricated. Synthetic doesn't go away as fast as conventional oils. That's why you can thin it to 100:1. I'm sure you'll find 100:1 works just fine.