I use about 1/4 to 1/3 of can every fill up the 1200A when I remember to take it with me. I think the can tells you how much to use but who needs instructions. Don't ever fill up the 6 Speed so I just dump a little in when I put gas in it, only 5 gallons at a time. I have also dumped a little at a time down the carb with truck idleing, just enough so it doesn't stall. Seems to clean things a little.
There are other products out there that do the same thing but I have had the best luck with Seafoam.
Disclaimer: I do not own any stock or in any way connected with the company but I should at least bought stock in the company before I started using it.