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  1. #1

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    Angry Walbro carbutettor problem

    I have a Zenoah 62cc engine with the usual Walbro carb. fitted. My problem is that after leaving the model for more than a week or 10 days or so, the carb. will not pump fuel through, it seems the valve flaps stick shut and I have lots of trouble attempting to start. The operating air passages are clear, when the engine finally starts, it runs normally.When flicking over the prop, it is obvious no fuel is flowing, as I can see there is none in the Tygon fuel pipe, even when the choke is closed..I can only get a start if I remove the diaphragm cover, and drench the carb with fuel, even then it sometimes will not start....I have fitted a new diaphragm service set, still no luck.I can only think that it may possibly be the type of oil I am using causing the flap valves to stick.Any help very much appreciated - I'm just getting nowhere fast!!
    Straighten up and fly right

  2. #2
    earlwb's Avatar
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    What I do is leave the fuel in the carburetor when I am done flying for the day. I drain the fuel tank but I plug the fuel tank's vent line too. This leaves the fuel in the carb to help keep the diaphragms from drying out. I started doing this after I realized that my trimmer engine, leaf blower, chainsaw, lawnmower are never drained after I use them and they run for years like that. The engines are a problem to start after having sit idle all winter, but usually it isn't a big deal to get them running eventually. I have had planes and engines sit for several months and they still start right up and run for me.

    Anyway, it sounds like the fuel is drying out and leaving the oil residue behind. That can make the diaphragms sticky and the little flapper valves on the pump diaphragm would stick and not allow it to pump like it should. But also the fuel passages and jet orifices may get clogged or obstructed with old oil residue that is drying out on you. So yes it can be a pain to take the carb apart and flush it out good and then get it back together and have the engine running.

    I have had good luck using Stihl HP Ultra synthetic oil. It doesn't seem to dry out and clog fuel passages or get as sticky as the mineral oils do. So you might give it a try and see if it helps.
    Club Saito #722, Sig Kadet Brotherhood #80, GlowHead Brotherhood #14,
    AMA # 928076

  3. #3
    All Day Dan's Avatar
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    Kevin, Change the screen and see if that helps. I use Stihl HP Ultra also but run the carburetor dry at the end of the day. What type of oil are you using? Dan.
    Dan

  4. #4

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    Which diaphragm are you using? The brown colored one is much less prone to stick than the black ones.

    All in all, I have seen this problem in carbs that have set over a long period but never during short term storage.

  5. #5

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    Thanks for all your suggestions! (the reply button doesn't seem to work )I have been using Ryobi synthetic oil (mainly used in chainsaws, strimmers etc.) but will now try to get hold of some Stihl HP Ultra oil.The diaphragm is black colour - I didn't know there were different colours, I'll try and get a brown one. Presently trying a paper-thin fibreglass type, but this seems to dry out like the others.I'll also try to seal the carb. up, with fuel in, and see if that helps.Thanks again, everyone!
    Straighten up and fly right

  6. #6

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    i'm not sure it makes a difference but I only use genuine Walbro branded parts kits. Some kits come in plain white bags and their source and quality is completely unknown. Stens kits also seem to work well but I still prefer Walbro.

  7. #7
    All Day Dan's Avatar
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    Here's the story about the diaphragms. Dan.Click image for larger version. 

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    Dan

  8. #8
    av8tor1977's Avatar
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    Nowadays I would take off that "good" rating on the black rubber ones....

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  9. #9

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    Kevin

    Seeing as you are on the other side of the river so to speek been running my 62's for the last few years on ave gas 100 and syn syn oil at 50:1 but I do add 1oz of sta-bil, or sea-foam per gallon, you will have to do the conversin, it also keeps the fuel from getting sticky, also I all ways leave the carb's wet.


    Cheers Bob T ;

  10. #10

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    If it were my carb, I would remove the diaphragm and then pull the needle and see if it is gummed up where it seats. I would also go with the stock balck diaphragm that came with the engine. The fiberglass and the blue diaphragms tend to wear out faster than the as equiped black one.

    Reading your symptoms, I believe what is happening is the diaphragm may be stiff. Removing the cover and placing gas inside tends to loosen up the rubber. I am currently away on a job and I do not have my Walboro manual with me. I believe the Zenoah uses a KT--- overhaul kit which can be found at most lawn mower shops. If you do the overhaul do not bend the tab that the needle rides in.

    Hope this helps.

    Glenn
    When all else fails pull the right stick down!

  11. #11

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    Are you 100% positive that your feed line isn't loose on the nipple inside the tank or has a pin hole or slit, when it happens the palne will run on the ground but once up will immediately go deadstick at least it happened with mine, the tube was loose on the nipple inside the tank.

  12. #12

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    Thanks again for all the suggestions!I stripped the carb. this afternoon and reassembled it with the same gaskets, as I don't have a repair kit . Still couldn't get the carb. to pump sitting on the ground normally, despit flicking and cursing for half an hour Eventually got the engine started by raising the tail end high, to give a slight positive head at the carb. end.. When started the engine ran normally and re-starts OK. I have stored it with a full tank, and the tail end raised to keep the carb. wet. I'll attempt to start it again in a week's time and see if this has cured the problem. (had the engine running on full power for 5 mins, no problems, but not very confident it will start next week!)
    Straighten up and fly right

  13. #13
    Moderator w8ye's Avatar
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    If the check valve flappers in the pump are working correctly, the HDA-48 carb should stay full of gas for months as long as you don't run the engine out dry.
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
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    Original AMA #31261

  14. #14

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    If the correct pump diaphragm is at all pliable, the pump flapper valves are reasonably flat, the diaphragm is installed directly next to carb body (gasket next to the cover plate) and it is supplied with a good pressure pulse from the crankcase, it will pump ..... period! Remove any one of these components and it will not work correctly. When you inspected the carb parts did they look acceptable for use? Are you sure you have the correct pump diaphragm in place? Is the pulse hole open to the crankcase? On the G-62, a slight gasket slip can block the pressure hole.

    Also, the newer G-62 carb spacer blocks are noted for breaking or cracking. Inspect yours closely for possible damage.
    Last edited by Truckracer; 08-09-2014 at 04:37 PM. Reason: Added content


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