Fuel leaking Mantis

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yodapete

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  • Location: Teesside, N.Yorks
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Fuel leaking Mantis
« on: September 02, 2012, 20:39 »
A few months ago my 2-stroke Mantis started being tempremental, difficult to start and I had to jiggle with the choke to get it running right, so I took it to a local lawnmower service centre  for a service.  Big mistake.  They charged me a lot of money and after five return trips to the place I decided it was costing me more in fuel to keep going back so I cut my losses and thought I'd  try to fix it myself.  The problem that appeared after being "serviced" is that it leaks fuel if left standing or hanging up on its storage bracket. The fuel leaks out through the air filter. I bought a  carb overhaul kit from Mantis uk and fitted it, new diaphragm, gaskets, metering needle and spring and used a can of carburetor  cleaner to clean out all internals of the carb before re-assembly but the problem's still there. I did notice that sometimes when using the priming bulb with the air filter removed,  I could see fuel squirting into the throat of the carb. I always thought that the priming bulb drew fuel from the tank, through the carb and back into the tank but only when the motor was started did fuel pump into the throat of the carb to keep the motor running  Can anyone suggest a cure? Have I missed something when I fitted the overhaul kit? Do I need to box it up and send it back to Mantis for a proper service?
Regards
Yodapete
Yodapete

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Gwiz

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Re: Fuel leaking Mantis
« Reply #1 on: September 03, 2012, 07:27 »
You will see petrol squirting into the carb when the bulb is pressed, so don't worry about that.
It seems to me that your fuel tank is pressurising when in use. Not much of a problem when you are using the machine (because you are using up petrol, and helping to keep the pressure equal in the tank) but when you stop using the engine, the excess pressure forces the fuel into the carb and out through the air filter.

I'm no longer too familiar with the mantis machine, but I would have thought that it would have some method of allowing excess pressure out and air into the fuel tank, and it would seem that this is faulty on yours.
There might be a purpose built one-way valve, or it could be via the fuel cap.
Just to see if I'm right, when you next put the mantis away and hang it up, just release the fuel cap and see if it "Hisses" at you. :)

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yodapete

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Re: Fuel leaking Mantis
« Reply #2 on: September 03, 2012, 09:36 »
Thanks, Gwiz.  I'll try loosening the filler cap after I next use it.
 I know there's a little breather pipe comes out of the fuel tank so I'll check that's not blocked as well.

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smud6ie

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Re: Fuel leaking Mantis
« Reply #3 on: September 03, 2012, 11:35 »
How old is your Mantis,how many pipes are there coming out of the tank,
Are there two fuel pipes,one  from the tank to the bottom of the carb and one to the top of of the carb or is there also a third pipe that just sticks outside the tank with a breather vent on the end?When you use the pump can you see which direction the fuel is flowing in.
smud6ie

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yodapete

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Re: Fuel leaking Mantis
« Reply #4 on: September 03, 2012, 21:03 »
Hi Smud6ie,
year of manufacture 2004, so its a SV-6 2 stroke.  It does have three tubes into the fuel tank, one is a breather with one end into the fuel tank and the other tucked under the plastic motor housing.  The fuel outlet with the felt filter on the end goes to the bottom connection of the carb and the other tube goes from the top connection of the carb, back into the fuel tank.  When I've used the priming bulb in the past, fuel gets drawn from the tank in the bottom tube and squirts back into the tank from the top one.  The priming bulb gets almost full of fuel so its almost a continuous stream of petrol back into the tank. I've just tried pressing the priming bulb and there's hardly any fuel returning to the tank and it sounds like its just sucking and blowing air. The priming bulb will not fill with fuel.  I haven't remove the  air filter and choke mechanism to check if its squirting fuel into the throat of the carb, but I think its another strip down job. Any suggestions??
Yoda

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grendel

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Re: Fuel leaking Mantis
« Reply #5 on: September 03, 2012, 21:22 »
could be a split in the bulb, or I have seen some where there is a small hole in the bulb that you seal with your finger as you prime it, I had to renew all my fuel hoses on my strimmer and the pipe with the felt breather has to come from the pipe in the tank that just goes into the top of the tank, the return from the carb should stop there too and the pickup goes through to the clunker that sits in the bottom of the tank, but if the primer isnt sucking it either has a hole or a split, then only cost a few quid, and its best to take the old one (or better the whole carb) with you, most mower/ garden equipment places should have spares.
I had to work out my fuel pipes from scratch as the originals had rotted and broken.
Grendel
we do the impossible daily, miracles take a little longer.

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smud6ie

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  • Location: Monmouthshire SE Wales
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Re: Fuel leaking Mantis
« Reply #6 on: September 03, 2012, 22:05 »
yoda, if the carb is a zama pm me your email and I can send you a technical manual which you may find helpful.
smud6ie



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