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Thread: Problem with a O-200a

  1. #1
    algonquin's Avatar
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    Problem with a O-200a

    Hi Guys, just wondering if anybody has run across this. O-200a , new prop 69/48 on a C-150l. Plugs cleaned and check good, timing right on(28*), mag checks good, all cyl. 72-76 /80, EGT’s front cyl. 1235, back two 1160. WOT engine gets to 2300-2400 and starts running ruff, back the throttle out 1/2” engine smooths out and makes 2550 rpm. (Checked with a proptach). Before I start pulling the mags and checking EGap etc. and sending the carb out would appreciate your guesses, thank you, Tom

  2. #2

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    Problem sounds like a fuel flow issue causing a lean condition when your carb is wide open allowing max air into the engine. Check float level and fuel screens. Could be a pinched or partially plugged line or the Gascolator to carb fuel hose coming apart due to age or ethanol. Could be debris in the carb partially plugging the main jet or even the needle and seat not opening fully. It could also be the mixture valve in the carb not opening all the way due to the shaft being bent or full of crud. It sounds like lack of fuel or possibly to much air. I don’t see how a induction leak would only come into play at WOT though. Very first thing I would do is turn the selector valve to off and unhook the fuel hose at the carb and put it in a container of some kind then turn the fuel selector on for a certain time and see how much fuel you have collected. I’m not sure on a c-150 but I’m guessing that it should flow a 8 oz in a a few seconds on Both with half full tanks.
    Someone on here will be able to give you a closer amount.
    Dave
    Likes cubdriver2 liked this post

  3. #3
    PerryB's Avatar
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    Step one would be to determine the fault condition. Is it rich or lean? If it's rich, pulling the mixture out will clean it up. If lean, obviously pulling mixture is going to kill it.
    After Monday and Tuesday, even the calendar says WTF !
    Thanks Doug Budd thanked for this post

  4. #4

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    My opinion, Perry has the first step, That carb can go rich.
    If it is lean then more of the system is involved as Dave suggests.
    The fuel valve in a C150 is a simple Imperial one way valve, simply on or off. But there have been long term problems due to lack of maintenance causing the valve to not open fully. Even if it turns out the mixture goes rich, do yourself a favor and cycle the fuel valve, it should turn freely with little friction yet few do.
    It is rare anyone shuts off the fuel in this plane and far rarer that any mechanic services the valve since it requires defueling the plane.
    If you note friction when turning the valve it would be recommended to defuel the plane, pull out the valve core and apply Fuel-Lube to it, reassemble and it will work as it should.
    Someone here might be able to pull up the Service Bulletin that came out decades ago, I no longer have it at hand.

  5. #5
    algonquin's Avatar
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    That’s Charlie, I’ll do that, it’s a lean problem on this one. I changed the valve on one a couple years ago, nasty little job the way they have it mounted.

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    Should only need to pull the spool out of the top of the valve and lube it with Fuel Lube. But not having it in hand it could well be worst than that.
    I had an engine seize in flight many years back, that was a very interesting incident that I will not cover here but thank golly for a tail wind that day.

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