I wouldn't venture a guess, but those earlier engines were darn good engines compared to the later ones in the 90's when they were having manufacturing problems. Look on the bottom of the crankcase and see if there is a date inside a circle - that would be the year it was made. Also look at the fin by the spark plug - the earlier ones had a tall fin - later models had this cut off. Where did you get your Quadra? Did you buy it from me?

When I first started selling Quadras in 1977, I purchased them for $50.00 each, and sold them for $79.95. The ad above is from about 1980.