Fuel dripping from air filter - Kawasaki 340

Discussion in '2-Stroke Aircaft Engines' started by keith103, Nov 11, 2019.

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  1. Nov 11, 2019 #1

    keith103

    keith103

    keith103

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    Hi , My Kawasaki 340 engine has about 15 hours on it. I noticed some fuel drips on the port outer side of the front fuselage directly beneath and behind the carburetor. I have seen this for quite a while, and tightened all fuel hoses on and around the carb, but the drip-leak continues.

    Only very recently I figured that the air filter was damp and dripping fuel - not too alarmingly, but a few drops on each engine run / taxi run of about 15 to 20 minutes. Now that I know where to look, I notice that on shut down, the air filter is damp on the underside with fuel, and often a drop of fuel/ oil mix about to drip.

    The engine has a 310 main jet. It came with a 330 main jet from J Bird, but because of the elevation here of 5200 ft, I decided to go lower size on main jet. Other than that the carb is all stock.

    The clip is on middle slot out of five, but at this position I am getting CHT just right. It gets to about 350 at 6000 rpm steady ( max rpm is around 6300 to 6600 variable. CHT at max rpm is below 400)

    I have a plunger primer which I squeeze about 3 times before cold start. There is a choke too, but I turn the choke off about a minute after start up. It has electric start.

    The other day I goofed up and forgot to connect one spark plug wire after I changed the spark plugs, and kept cranking about 15 times before I realized the mistake. As I got down to connect the plug wire, I noticed a pool of fuel on the ground right beneath the air filter. So when it did not spark, the fuel was just gushing out; does that give any clue ?

    The drip itself is not a big issue I feel, but if that indicates a bigger problem, then I would like to learn what that is.

    All thoughts and suggestions appreciated.
     
  2. Nov 11, 2019 #2

    n3puppy

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    Is the engine mounted inverted? (Plugs down)
    How is the primer plumbed to the manifold?
    Can you get a picture of the mounting - especially the carb angle in relation to the engine.
     
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  3. Nov 11, 2019 #3

    kirbylee

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    I didnt get a chance to think about the leak that much, but my first thought was the float sticking just enough to keep it from seating and shutting the fuel off. I dont know how where else it could from.
     
  4. Nov 11, 2019 #4

    proppastie

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    stuck float, crud/corrosion at float needle, if it is a rubber tip, alcohol in fuel has ruined the rubber, have to change to all brass, and add a shutoff valve for when you park.....leastwise that is what I had to do for my tractor....better check with others on the aircraft carb. also bad float (does not float anymore) vibration can ruin a brass one and the plastic ones can go bad.
     
  5. Nov 11, 2019 #5

    Dana

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    2-strokes often have fuel/oil dripping from the air filter as there's a bit of backflow before the piston rises enough to close the intake port, so the filter may stay wet, no big deal. Now if it keeps dripping during storage, that's another thing, could be a bad float needle or seat.
     
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  6. Nov 12, 2019 #6

    Turd Ferguson

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    We used to call that "loading up" the bottom end with fuel.
     
  7. Nov 12, 2019 #7

    pictsidhe

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    Quite often this is a miniscule bit of dirt or grass stopping the needle seating properly. Do you have an inline fuel strainer?
     
  8. Nov 12, 2019 #8

    cheapracer

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    This.

    Before reed valves, soaked filters were quite common from crankcase blowback, especially if they were running a bit rich (or other carby issues), ign timing off or just from the choke.

    Poor ring sealing as well, but at 15 hours I wouldn't expect that unless they simply haven't bedded in well.
     
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  9. Nov 12, 2019 #9

    kirbylee

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    Was my first thought also. Cant imagine what else it would be.
     
  10. Nov 13, 2019 #10

    keith103

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    Thanks for your thoughts and ideas.

    The engine is mounted erect, and I use ethanol-free regular midgrade autogas. I usually shut off gas while shutting down engine, but when I forget to do that, I see no additional leak after shutdown. So most likely it may not be a bad float.

    The carb is very slightly tilted, about 3 to 4 degrees outwards from vertical, due to the shape of the inlet manifold which is tilted down a bit. The connecting rubber connector is bent opposite way, so it ought to straighten the bend, but it does not fully offset the tilt in manifold, hence the 3 to 4 deg tilt. Does that cause the leak. Leak is more at start up. May be the prop wash blows away any drips after start up.

    Dana's reasoning looks more plausible in this case. It may just be a bit of backflow due to overlap of two different actions during each sweep of the piston.

    Not sure if the 3 to 4 degree tilt of carb makes it worse ? The carb is tilted towards the air filter.
     
  11. Nov 13, 2019 #11

    proppastie

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    take the filter off to see if you can see anything going on.....I never had a wet filter in a motorcycle from "backflow".....The choke will pull lots of gas and cause drips....do you choke it....also the wrong size air filter will have a choke effect....the tilt towards the filter with a choke effect could cause drips and a wet filter. Whenever I had problems with a bike the first thing I did was take the filter off to eliminate one more factor and see the choke and slide as they work.
     
  12. Nov 13, 2019 #12

    Dana

    Dana

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    One other thing is that at low rpm, when a 2-stroke engine typically is vibrating a lot, the float bounces around so it's probably letting more fuel in.
     
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  13. Nov 13, 2019 #13

    cheapracer

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    My first full time job was an Apprentice Motorcycle Mechanic in a Yamaha motorcycles and Stihl chainsaws shop in the 70's.

    It's quite common (was).
     
  14. Nov 13, 2019 #14

    BBerson

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    In 1970 I rode a Rotax powered Skidoo that spit gas out of the carb. No filter, right in front of the driver.
     
  15. Nov 13, 2019 #15

    cheapracer

    cheapracer

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    And we would shave with 4" grinders!

    When men were men, Arrrrr!!
     
  16. Nov 13, 2019 #16

    pictsidhe

    pictsidhe

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    Boys used grinders, men used chainsaws.
     
  17. Nov 13, 2019 #17

    proppastie

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    I must not have noticed
    Maybe because my bikes were so finely tuned.
     
  18. Nov 13, 2019 #18

    cheapracer

    cheapracer

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    ..ouch! :p
     

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