Get a spray carb cleaner to clean around the old carb and the surrounding before taking it off so you don't get dirt into the new carb and the engine. Mantis gets very dirty, it's so easy to get dirt onto the new gasket and all.

I think it's just that simple, replace, hook everything up and try starting it. I won't mess with any adjustment other than the idle rpm first.

I got two of them at garage sale. First generation Mantis with the good Echo engines. Owner said they don't run and selling them for parts. Thats all it was dirty carb. One All I did was disassemble and clean it up used the old gaskets and diaphram It ran like a top afterwards which I done the exact same things as yugman suggested.

The other one was really rusty inside the carb and took alot more cleaning and a new carb. kit. (cost me 8 bucks). But, the end result was the same, runs good now. I kept one and gave one to a co-worker These were mid 80's models and set for a very long time.

Since you bought the carb already, I did not suggested overhault. But I think you should try doing it just for the knowledge and see whether you can fix it. Few dollars only, and believe me, you get a lot of satisfaction!!!! You can even talk louder here next time!!!! Just remember the orientation of all the stuff or by marking it. get a small can of duster from the computer store and blow the holes.( you can still use it on your keyboard if not for anything else!!)