Won't stay running...

I had the same problem with my mantis. It would start fine after a few pulls, but had no power. I changed the plug, replaced the carb completely...nothing helped. Took it to a shop and paid $70 for a tune up that didn't help at all, and the shop owner just said "sorry".
After everything else was done, I pulled the cover off the muffler, (3 screws) then removed 3 screws over a small spark arrestor screen and found it was clogged...cleaned it and guess what...IT WORKS FINE NOW!

The best and easiest fix I have ever done to a small engine. I felt like an idiot, because the exhaust side of the motor MUST be clear to work properly on small engines. The only reason I was removing the muffler in the first place was to check the compression and VOILA!!!

An easy and quick fix I recommend for all Mantis tillers before you waste money on carb issues (which is what the company will tell you to fix to solve this problem).

I followed Mantis' insructions and cleaned my muffler screen, (it wasn't even dirty), then I took apart the carborator and soked that too, (it wasn't very dirty either) After all this I finally got confident to deal with the only thing left, the 3 screw adjustments.... The only way to start my Mantis was with a rubber band holding down the clutch, and of course I have the tines OFF. I played around with the High and Low screws until I had the tines bar spinning as fast as possible. This took a bit of playing around, but it became obvious that the H controlled the rotation, with the clutch held in by a rubber band. Then I took the rubber band off the clutch and much to my surprise it didn't stall but the rotation slowed to a stop which is what it is supposed to do. Next I adjusted the L screw so it sounded "right" I just tried turning first one direction and then back the other direction until it seemed right. It stalled a few times, but I just started it and kept playing with the secrws.
The adjustment of the bottom screw must be for the idle, (not exactly sure, and no-one at Mantis could tell me) but I played with this screw until I could take the rubber band off without it quiting. It is not an exact science but after months of not working I was able to rototill my garden and new hedge row before the rotation slowed down again.
The final fix was a new sparkplug because I read that the coil was inefficient for the engine and this was the only variable left. I might have changed this sooner if I didn't misplace my plug wrench. After installing the new plug I once again needed to hold the clutch in to get it started (remember to REMOVE the tines) but was able to reset the screws so it was adjusted as before. Time will tell how long this new plug and adjustment will last. Because the new plug required me to adjust the settings, I believe that the plug is the cause of these problems. It is the only variable that had any effect. Happy tilling, Marie

I had a problem with keeping it running under load.After reading several posts about fuel I looked into the fuel filter and found a small secondary disk type filter beneath the fiber filter.I removed it and it started up on the third pull and ran like new. I think the disk was keeping fuel from the engine.

You should check the plastic bubble that is used to prime the engine. A small pin-hole leak in this will cause the engine to stall as soon as the throttle is depressed, but it will idle fine.