Mixtures

I've read all kinds of reasons to use different fuel/oil mixtures. What is the best for a 1978 ridden by an old guy with no intentions of racing and not wanting to fog this part of Ireland ?

Follow the oil manufacture's recommendation and you'll be fine. Be sure to adjust your jetting to suit the air fuel ratio.
More oil = lean air fuel ratio / less oil = rich air fuel ratio.

There are literally volumes of discussion on this topic and you're right, just as many opinions. Me, I opt to run a 32:1 fuel/oil ratio. You can run leaner than that and many people do, but I've always run this ratio in all the 2 strokes I've ever owned for over 45 years of riding. Why 32:1? Gives good cylinder and rod bearing lubrication (maybe reducing engine wear vs. a leaner ratio....but I'm sure someone would debate that as well), plus it's an easy mix to make with 4 ounces to a gallon of gas.

Just to expand on what Ron said re: mixture. Less oil in the mix means that less gas is displaced with that small amount of oil, thus there's more gas available to combust with the same given amount of air - making a richer combustion air/fuel ratio. The reverse is true with more oil being used in the mix (less gas available, leaner air/fuel ratio). The point is that your oil/fuel ratio will have an impact on your air/fuel ratio delivered by the carburetor. Once you decide on what fuel/oil mix you'll be using, then you should tune your carburetor jetting to achieve the desired combustion mixture setup. If you decide to go up or down the scale on oil ratios, then you need to confirm and/or re-adjust your combustion air/fuel mixture.

And oh....congrats on your first dirt bike. Even at 67 it'll make you feel like a young man again. I'll be 60 in a few months and sure do hope I'm still riding at your ripe old age! :-)

Many Thanks for all the information guys, it's invaluable ! I may be 67 but my wife says I never made it past 20. I could really learn to love these things. The really good news is I accidentally fell into a great group of riders !

Many thanks for all the information, it's invaluable ! As for taking this up at 67 my wife has an answer. She says I never made it past 20. I'll go with that. It looks like I fell into a great site. I could really learn to love these things !

Since you now qualify officially as a vintage dirt bike owner, no matter what the brand, you may also find the Vintage MX forum helpful
http://www.vintagemx.us/message_board/viewforum.php?f=2&sid=f6f7ea2ee6635ac20ed1a47298de8eb5

Thanks, Good call, great site.