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Thread: Marvel Schebler Question?

  1. #1

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    Marvel Schebler Question?

    I am looking at putting a c-85-12 Stroker on my new PA-11 instead of my c-90-8 the question going through my head is now that the 85 is basically an 0-200 can you use a carb numbered for the 0-200 or do you have to use the one for an c-85? I have read some threads where your insurance may not cover you with the wrong carb?

  2. #2

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    Unless the STC says otherwise, to be legal you need one of the carbs listed on the C85 TCDS.


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  3. #3
    cubdriver2's Avatar
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    The 4894 works great on a stroker, I know of 2 . But a Stromberg from a C90 will give you 50 more static RPM. In 30 years I've never seen or heard of anyone being questioned about which carb they were using.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  4. #4

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    Things are changing.

    But 30 years ago IAs were routinely approving major alterations by signing 337s. I have fixed a bunch of those in the last year or so, and I don't do this for a living.

    Do what Dave says and strive for legality, at least on paper.

  5. #5

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    I am trying to make this one as light as possible and have one with good paper work as mine got really screwed up after a crash in the 80's. I love the mods on mine and plan on an identical plane only a hundred pounds or so lighter so I can have a plane that will perform a little/LOT better than mine does and have the convenience of a starter as I get older. Question is basically in my mind the more HP the more fuel it needs to be fed to achieve that. Thanks for the replies.

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    JP's Avatar
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    Douten, we had issues with a carb with an accelerator pump that while approved for the 90 did not work in an -11 due to pressure differential of the cowling. It would stumble. Put the M/S back in and that was cured (until the float sank, but that's a story for another day--perhaps in the Newbie Thread). 85 stroker has the torque the -11 does. 0200 is a great engine but different torque.
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special
    www.bloomerrussellbeaupain.com

  7. #7
    cruiser's Avatar
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    Please share the story on the sinking float. M/S has a 15 year old SB on that issue that is slow to be complied with. Mandatory IMO.

  8. #8
    JP's Avatar
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    Quote Originally Posted by cruiser View Post
    Please share the story on the sinking float. M/S has a 15 year old SB on that issue that is slow to be complied with. Mandatory IMO.
    Absolutely. It has some useful lessons that I'm happy to pass along. Four of us were headed from a grass strip over to the Floatplane Mecca for lunch. We were all on skis. Preheat, warmup, runup etc. all went well. Taxied out and departed. I was the last in the flight to take off. All normal. As I climbed out and was just starting to catch up things got really, really quiet. I pushed over to 55 and started to run the basic restart checklist. Nothing. I started a gentle turn back to the field. I was a half mile or so away. I let the boys know I was without power and returning to the field and they wheeled around to watch the fun.

    Here's where I made a mistake. I had the field made and was plenty high. So, I started a 360 to shake a bit of altitude so I'd land closer to the hangar. Dumb idea. As I came halfway through the turn the landing spot was fading out into the distance. I was still in the turn and starting to unconsciously pull as the ground neared. The left wing started to wobble a bit as I tightened up the turn. I pushed and leveled and set up for my alternate landing spot.

    Seconds later I set down in a farmer's field across the road from the airfield. When I clambered out there was fuel spilling out of the carb. The other boys landed and walked over to the airplane. We started it up and taxied down to the road, put it on dollies, rolled it down the street 100 yards, popped it over the snowbank and taxied back in to the hangar. The engine ran fine at low throttle--anymore and it would bog out.

    The next day we pulled the carb and hauled it over to the shop for further examination. Upon disassembly it was clear that there was gas in the metal float. Further examination revealed a pinprick hole in same that caused it to fill up and sink. The best guess is that it was already partially sunk and sank the rest of the way in operation, flooding out the engine with an unrestricted fuel flow once aloft.

    The great, great thing about the MS carbs is that they are otherwise pretty bulletproof and overhaul kits are readily available (since we had it apart we overhauled it, too). We opted to repair the float with silver solder and leak tested in gasoline (do not leak test in water as it has a different viscosity). We set up a head test tube and followed the MS instructions for setting the float height. Pretty straightforward. Static check, flight check, returned to service.

    At the end of the day the simplicity and general reliability of the MS carb outweigh the inherent fuel inefficiencies of such an ancient carb. Very few moving parts. And, certainly, a bit of an achilles heel with the float. So keep an eye on them.

    Oh, and one more thing. All of this occurred on skis. My first takeoff and landing on skis. Good fun and a learning experience all the way around. And, yes, somewhere there are pics of us dollying the airplane down the road....
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special
    www.bloomerrussellbeaupain.com
    Thanks CamTom12, cruiser thanked for this post
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  9. #9
    hotrod180's Avatar
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    Quote Originally Posted by JP View Post
    ..we had issues with a carb with an accelerator pump that while approved for the 90 did not work in an -11 due to pressure differential of the cowling. It would stumble. Put the M/S back in and that was cured .....
    More on the first carb-- what was it?
    First thing comes to mind is a stromberg but I don't think those have accelerator pumps.
    And curious how the pressure differential of cowl would make a difference in carb ops--
    pressure carb maybe?
    Cessna Skywagon-- accept no substitute!

  10. #10
    Gordon Misch's Avatar
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    And curious how the pressure differential of cowl would make a difference in carb ops--
    I was wondering the same thing. But then got to thinking that the carb bowl is vented to the air inside the cowl, and the balance between that ambient pressure and the pressure from the fuel in the tanks could affect the fuel level in the carb bowl.
    Gordon

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  11. #11

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    I have almost no experience with the MS carbs. One quit on me on final approach to Pecos - not even sure it was a legal installation - 65 HP Cont. - Turns out it had unbolted itself - the top half was getting ready to release the bottom half. No safety wire. I was only 77 then, and agile enough to fix it on the ramp, with Kermit's help.

    Lots of experience with Strombergs, starting with the model 97 - chromed, thanks! Easy to work on, and almost bulletproof. Never had one quit.

  12. #12
    JP's Avatar
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    Quote Originally Posted by hotrod180 View Post
    More on the first carb-- what was it?
    First thing comes to mind is a stromberg but I don't think those have accelerator pumps.
    And curious how the pressure differential of cowl would make a difference in carb ops--
    pressure carb maybe?
    If I recall correctly it was a successor company Precision Airmotive carb with an accelerator pump. A modern MS for the 0-200 and 90. One of the MLT Campbell Boys did a bit of research and concluded that while approved for a C90 it was only for use on certain airplanes (the Aircoupe, for example). The loss of power/stumbling issue generally only occurred during a climb and got your attention for sure. I took that carb off, sold it and never looked back.

    On the MS the only other thing that we've encountered was a worn needle and bracket, which can cause a brief hang up leading to loss of power. The needle, if worn, can get stuck on the arm bracket. The diagnosis is to tap the side of the carb and see if power increases. Easy to fix with an overhaul kit.
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special
    www.bloomerrussellbeaupain.com

  13. #13
    mvivion's Avatar
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    My -11 had a C-90 with a M-S carburetor, including accelerator pump. Worked great, and I installed a mixture control cable, which made prop starting a lot safer.

    That mixture control also permitted leaning at altitude. I ran that plane right next to an -11 with a Stromberg carb at 10,500 msl, and with the mixture leaned on that M-S carb, I used considerably less fuel.

    I'd go there again. You can keep all your Strombergs.

    That said, the new carbs that Cub Crafters uses on their CC-18-180s really, really don't like cold weather. Move the throttle a bit too fast, and the engine will die.

    Don't ask how I found that out.

    MTV
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  14. #14

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    Interesting thread. I have had to delete the 'one-piece' venturi from M/S C90 carbs to get proper running several times. Last year I had exactly those same problems on Lycoming O-235C - 108hp. Only solved by reverting to the original 2-piece venturi.

  15. #15
    hotrod180's Avatar
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    I think they revised and/or eliminated the AD requiring the one-piece venturi due to that.
    Keep the two-piece but inspect every year.
    Cessna Skywagon-- accept no substitute!
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