Mpg, Dieseling, Pinging

[79blazer]

Hello when I got my blazer 1.5 years ago, it ran ok on 87 octane gas, then it started to diesel, which it try to run after its shut off, and light pinging sometimes. Worse if its hotter. So I put 89 octane gas in it, because I know pinging is very bad. I didn't know how to adjust the carb, so I switched the thermostat to 165 and 87 gas and it was fine. Later it started to ping/ diesel again, so I ran 89. Then about a month ago I forgot and put 87 in it and it dieseled. I started 91 gas now with that 165 tstat in there and I thought I heard it diesel just a little twice in the last week. It doesnt seem that powerfull. It sometimes hesitates when lightly getting on the gas. Also if it sits for 12 hours or more it won't even try to start until about 5 seconds. As if I have to wait for fuel to be pumped? MPG was 10-12 city for awhile backseat in 235 75 15 bald tires. Now its a consistant 11.4-11.6 mpg no back seat, some loads and 31x11.5 tires. I gave it the STP FI cleaner a year ago. I don't know what carb is on it but I think its original 2 bbl. Plugs and wires are a year old. What name/model of carb is it? How do I tune it? Can you buy better jets to better mix the fuel? thanks david