Sandiegojc, sorry to hear of your bad experience with Mantis. Generally, they are reliable machines. If you have the 2-cycle engine (the one that requires you to mix oil into the gasoline), I suggest that you remove the muffler and scrape away all the build-up, then re-install the muffler. That build-up is a fairly common problem with 2-cycle engines, and clearing it away frequently fixes the problem.

My Electric mantis starts right up, don't smoke, and real quiet. Only have to take the tines off every now and then and clean-up the shafts. It has three speeds, but I hardly ever get it out of first gear. Has far more torque than those nasty gas models. Runs just fine off 100 foot extension cord.... I had real old two stroke model with the echo engine and I got tired of doing the same things you did. So I got ride of it on #raigs listers. had lots of calls and had no problem dumping it for the electric Jim Dandy....

I inherited a 2 stroke Mantis. It is about 10 years old and runs fine. It is great in my raised beds. I run it just like my old saw. Blip the throttle and run it wide open

2 cycle Mantis use the 21cc engine made famous by Echo. It has been the work horse for years in commercial environment. Reliability is beyond compare. If you have problem, chances are high that you don't know what you are doing. Particularly if you had it serviced many times.

When you cold start, prime the bulb 7 to 8 times, close the choke all the way, don't touch the throttle and just pull. When it starts, quickly open the choke all the way, don't even touch the throttle. You monkey with the throttle while trying to start it, the engine can get into a stubborn mode and you are going to have a hell of a time starting it. Just follow my instruction.
When you stop the engine and want to start again while it is hot, don't prime, don't throttle, just pull and it will start in one pull.

I forgot to mention, sometimes when you pull, it tries to start but stop. In this case, open the choke all the way and pull, it almost always starts on the next pull. Remember never touch the throttle throughout the whole process. You touch the throttle, that's when you get into big problem. The engine never start on the first or second pull, usually like 4 to 5 pulls, never beyond. The method I described in starting works for Honda, Echo, Maruyama, Shindaiwa that I have. I never have to alter from this all these years.

Remember, don't touch the throttle.