After many years of dithering, I finally decided to get a Mantis. I found a used one for $80? $100? on Craigslist and bought it. It’s great! I found edger and dethatcher parts for it and it’s ready to rock and roll. This note will hold some details about it and its history.
Last summer (2015) I edged all the sidewalks with it and tilled up the big mess where the tree in the inside front lawn was removed and the stump ground out. Despite its size, the thing is a beast! I drained the tank and ran out what fuel was left in the carb and put it away for the winter.
When I tried it this spring, it wouldn’t start. Not even a pop. Yeah, the fuel was a little old (whatever was in the snowblower/lawnmower can – of course with Stabil, which is great), mixed fresh with oil to 50:1, but I doubted that that fuel was an issue. I choked it and pulled a lot, but when I pulled the plug, it was completely dry. Looks like a carb issue. C’mon – I even ran it dry, which is a lot more than I ever do for any of my other small engines! I drained the tank and put it away for a couple of weeks.
When I got back to it I’d decided to disassemble and clean the carb. I had a tuneup kit (almost the right one) with fuel lines, plug, and air filters on the shelf, but no rebuild kit. If I got in trouble, I figured I could probably find a kit at some local lawnmower place. And I’d watched a couple of rebuild videos on YouTube. That’s a pretty amazing resource.
The carb came apart easily, and looked pretty clean inside. I sprayed carb cleaner kind of randomly thru holes, but didn’t know where it should come out. The first glitch was when I went to reassemble the machine. Since I had new fuel lines (and fuel filter and check valve and tank grommet), I figured I’d install them. But the hoses 
were way longer than the originals, and the 3-hole grommet was too big for the hole in the tank. The parts in the kit I got are on the left, but the originals look like the pic on the right. The old grommet was still OK, so I cut the other hoses down and put it together.
You’re supposed to pump the primer bulb on top until you see gas in the return (clear) line. I’d replaced the quite dark (but still flexible) bulb with a new clear one, but it didn’t seem to do much. I did finally see some fuel in the clear line (a red herring: it was coming from the tank, not the carb!), but the bulb wouldn’t flex back to normal after pressing on it. Grumble, cheap chinese parts, grumble, put old bulb back. Same behavior. Choked it and pulled a lot – but still not even a pop and the plug was still dry. Rats.
I took the carb off and apart again, sprayed some more carb cleaner at it, and pondered the primer bulb and its plastic environment. Sucking and blowing on the (top) fuel return nipple, there was very little flow, but it seemed like a check valve (flowing out of the carb). The brass insert apparently at the other end of the return fuel passage could be there to hold a check valve in. But I could barely suck any air thru it. I worked a bit of wire insulation into the hole and could hear/feel what could be a sticky flap valve.
After working it a bit more, I blew carb cleaner in to the brass fitting and it sprayed out the return nipple! I’d done that before, but nothing came out. (A tech doc I found later confirmed that the primer bulb blows fuel/air out the return line thru the check valve, and then sucks fuel thru the carb passages, thru an inbound check valve and into the primer bulb.)
Encouraged, I put it back together again and pumped the (new, clear) bulb. It filled with fuel! So that’s how it’s supposed to work! Some normal steps later, it started and ran. A couple of tweaks to the low and high speed needles, and it was running well. I tilled the little flower plot next to the garage (just in time for Lauren to plant the flats of impatiens she’d just bought) and the little Mantis did a terrific job. I should be able to do the edging the next nice day. Oh yeah – this was all with the same old fuel I’d tried in the beginning. Stabil is great stuff.
For the record, here are some pics. Looks like it’s pretty old, based in part on the white handle grips, and in part on the C1U-K17 carb. I’m guessing the newer tanks take the larger 3 hole grommet. The air filters in the tune up kit were the right shape, but a little too large – 
presumably another later update. I was able to poke them into place with a screwdriver. The SV-4B engine ID is old, too.
The machine ran fine when I got it, and this carb cleanout is the only work I’ve done on it (so far). I really should check the gear case grease, and I sort of think there’s something about the muffler that should be checked. I haven’t done anything to the plug since I got it (except pulling it to look for gas).
The used dethatcher I found on Ebay seems to be in good shape, but doesn’t have the sheet metal cowling. I found a video of a guy (Jim Barry) doing dethatching with a Mantis. He pulled the cowling off briefly as a demo. It threw the thatch everywhere without it. Thanks, Jim! I should be able to make something pretty functional from the 22 ga sheet steel from the animal cages Ed S tore out.