Mantis Tiller

   / Mantis Tiller #1  

Wburton

New member
Joined
Oct 21, 2016
Messages
17
Location
Advance, NC
Tractor
Kioti
Hiya,
Got a "good" Mantis that's driving me nuts!! I bought it new and it's always been 'good' but temperamental. Usually a slight carb tweak and off I go. I'm good on small engines (2&4 stroke) but I'm stumped.
This one is a 10 yr old 2 stroke. Starts on 2 pulls and runs great- for about 2 minutes then quits. Starts right back up with a pull. Throttles up and down fine. I rebuilt the carb. No help and no change. I swapped it with another Mantis Zama carb. No change. All new fuel lines, vent, plug, cleaned air filter, cleaned muffler. No change. Bought a whole new OEM carb. No change. Compression is great. Visual inspection thru the muffler port and the piston and rings look fine. I only burn non-eth 93octane, 50/1 mix fresh.
So today I heard the vent line might not be working right. Ran 2 hours of tests with a stop watch. I can crack the gas cap open and leave it on fast idle (via the throttle cable adjustment screw) and run a half tank of gas. But when I screw the cap tight it will 'stall' in about 4 minutes. I swapped the brand new vent line with 2 others I have on hand. All are spotless and clean. I get the same results.
I've got tractors, gas and diesel, 6 chainsaws, a '70s cast iron Ariens Rocket 7 tiller, Shindaiwa blowers, weadeaters, push mowers, 4 riding mowers and a big JD 0-turn. I maintain and do all the repairs on all of them!
But- this tiny little thing is killing me
 
   / Mantis Tiller #2  
Sounds like the same machine and age that I have. I recently had to replace the primer bulb. The old one was cracked and leaking air. My first thought on yours was a dirty, partially plugged, fuel filter in the tank. But now it does sound more like a gas cap that isn't venting as it should. Good luck with it.
 
   / Mantis Tiller
  • Thread Starter
#3  
Yeah, new primer bulb along with the new carb, fuel lines and filter and vent, air filter, spark plug, muffler screen clean, proper fresh fuel/mix...
Mantis says my compression should be 120-140 psi. I've got around 102-105. They say it won't continue to run below 120. It's a possibility but I don't think so. The dude that checked it says anything above 95 is ok. Over 100 is good.
After 2 hrs of running it with the gas cap open and closed, it is evident it's not venting properly. Now I just have to figure out why.
Thanks!
 
   / Mantis Tiller #4  
So vent the cap... You have a drill, don't you?? lol

SR
 
   / Mantis Tiller
  • Thread Starter
#5  
Funny you would mention that. I actually have a cap off a scrap mantis and drilled a small hole in it just a bit ago. It worked but I'm getting gas out of it when it's bouncing around. I think I need to add some sort of "deflector" inside the cap.
 
   / Mantis Tiller #6  
Does yours have the little vent line filter that goes up under the engine shroud like mine? If so, that may be clogged.
A356000031 Fuel Tank Vent $6.22

eReplacementParts.com
 
   / Mantis Tiller
  • Thread Starter
#7  
Does yours have the little vent line filter that goes up under the engine shroud like mine? If so, that may be clogged.

Yep. Brand new. Actually tried 3 new ones just to make sure one wasn't defective
 
   / Mantis Tiller #8  
Once you put a hole in gas cap your screwed. Gas will keep coming out. sounds like your missing something on the venting but I don't know what.
 
   / Mantis Tiller #9  
Here's a thought.
Go to your Husqvarna dealer and get a duckbill valve HOP 530026119. Measure the OD and then enlarge the hole in your gas cap just enough to firmly seat the valve by pulling through from the bottom. You want it tight enough to have a good interference fit. That will stop the gas from coming out ans give positive venting to gas tank.
I would use a touch of Permatex Aviation sealer on the OD of valve when installing it to make sure it stays in place.
Just make sure cap is degreased .

You shouldn't have to do this, the Mantis vent should be working properly, but this will save you gas cap plus giving you venting.
 
   / Mantis Tiller
  • Thread Starter
#10  
Interesting idea.
I'm still bumfuzzeled as to why it just started this. I bought it new.
Oh well...
 
 
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