I have an Echo weed whacker. I have been using 87 octane gas for years, mixed with oil, of course. I was reading the manual recently (ha,ha it's been years and I just started to read the manual) and I noticed that it says to use 89 octane gas mixed with oil. I am wondering if it really makes much difference to use 89. Perhaps my weed whacker would be happier? I like using 87 because it costs less.