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Thread: ma3spa carb

  1. #41
    zenairdave's Avatar
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    Quote Originally Posted by Pacerfgoe View Post
    No, I'm talking of the Marvel Scheblers. The carb I have on my Pacer has this feature.
    The Ma3spa does not have an economizer. The Bigger MS carbs do.

  2. #42

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    Any updates on this issue? I have an O-200A with the same problem. I have installed new carb, cylinders, and checked many things. Still can't get away from too rich at full throttle. I lose about 50 rpm when slowly going to full throttle from 75-80%. I can get the rpm back by leaning mixture.

  3. #43
    zenairdave's Avatar
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    Quote Originally Posted by mk.temp View Post
    Any updates on this issue? I have an O-200A with the same problem. I have installed new carb, cylinders, and checked many things. Still can't get away from too rich at full throttle. I lose about 50 rpm when slowly going to full throttle from 75-80%. I can get the rpm back by leaning mixture.
    In principle, this is an easy tuning problem to fix, in reality, it is not. The internal circuits that come into play at full throttle are too rich. In most carbs, that is simply a matter of changing the Main jet to a smaller size. When the carbs that we are talking about went from the two piece venturi to the one piece, the internal negative pressure changed (suction) which caused the now "famous" rich running conditions at full throttle. So, back to the rich running at full throttle issue. to reduce the main jet size on this carburator requires a new emulsion tube. These are not sold in different sizes for this carburator. Different sizes are made for different carburators if you can figure out what sizes "standard" tubes are. To further compound this, after speaking with the current manufacturer, they test flow each carb and drill the emulsion tube to get the "book" flow. If this is true, there is no way to know what size emulsion tube is in each O-200 carb. All I can say is I think the one in mine needs to be smaller. The tubes were very expensive $200 - $400, I did get the stock size specification but have not taken my carb apart to see what size it is. At this time I have been operating at 85% throttle position for climb out rather than leaning at this critical stage of flight. I have this option because my cub does not really require all 100 ponies to get off the ground.
    Of coarse there are other things that can cause rich conditions that must be eliminated before adjusting carburation to solve some other problem. Leaking primer, restricted air filter, leaking carb heat are but a few.

  4. #44
    cubdriver2's Avatar
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    Quote Originally Posted by zenairdave View Post
    In principle, this is an easy tuning problem to fix, in reality, it is not. The internal circuits that come into play at full throttle are too rich. In most carbs, that is simply a matter of changing the Main jet to a smaller size. When the carbs that we are talking about went from the two piece venturi to the one piece, the internal negative pressure changed (suction) which caused the now "famous" rich running conditions at full throttle. So, back to the rich running at full throttle issue. to reduce the main jet size on this carburator requires a new emulsion tube. These are not sold in different sizes for this carburator. Different sizes are made for different carburators if you can figure out what sizes "standard" tubes are. To further compound this, after speaking with the current manufacturer, they test flow each carb and drill the emulsion tube to get the "book" flow. If this is true, there is no way to know what size emulsion tube is in each O-200 carb. All I can say is I think the one in mine needs to be smaller. The tubes were very expensive $200 - $400, I did get the stock size specification but have not taken my carb apart to see what size it is. At this time I have been operating at 85% throttle position for climb out rather than leaning at this critical stage of flight. I have this option because my cub does not really require all 100 ponies to get off the ground.
    Of coarse there are other things that can cause rich conditions that must be eliminated before adjusting carburation to solve some other problem. Leaking primer, restricted air filter, leaking carb heat are but a few.
    Have you tried flying it without the air filter on?

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

  5. #45
    zenairdave's Avatar
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    No but I have changed it twice. Foam style that bracket says replace yearly.

  6. #46

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    Make sure the screws on the float bowl are not coming loose, This will cause it to run rich. It is a rather common problem.
    DENNY
    Likes swoeric liked this post

  7. #47

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    id really like to have a small study with AFR meter and just give it a go.. lets see just where we really are.. it seems like my 85 hp is really undercarbed at times.. would not be that difficult to bench a couple carbs on a plane in a day with two or 3 guys swapping parts or drilling jets.. id think you could ebay the jet parts and make a spread sheet quick.. same with venturi sizes

  8. #48

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    I have tried disconnecting the primer, also making sure no carb heat is leaking past the flapper. I ran it without the foam air filter element, at part throttle it ran terrible, only improving if I turned carb heat on. It originally had a 10-4894-1 carb factory overhauled in 2001. I replaced it with a MSA factory overhauled 10-4894-1 earlier this year. Both carbs lost rpm at 85% or greater throttle. With the new cylinders I moved the timing from 24 to 28 with little change. It runs pretty good otherwise. The aircraft is a 1965 Champion 7ECA. The air box is smaller than that of a cessna 150, I have thought about installing a 150 air box and testing to see if that helps. I find it hard to believe that all cessna 150's run this way. It is very noticeable on takeoff, has a light stumble right at the last bit of throttle travel. Pulling it back to 85% or so cleans it back up. I have read about the idea that the carb adds extra fuel at full throttle for "cooling", if I thought there was some sort of passage in the carb that provided this extra fuel, I would pound some sort of plug in it and be on my way. I would think this would show up on a flow bench.

  9. #49
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    Quote Originally Posted by mk.temp View Post
    I have tried disconnecting the primer, also making sure no carb heat is leaking past the flapper. I ran it without the foam air filter element, at part throttle it ran terrible, only improving if I turned carb heat on. It originally had a 10-4894-1 carb factory overhauled in 2001. I replaced it with a MSA factory overhauled 10-4894-1 earlier this year. Both carbs lost rpm at 85% or greater throttle. With the new cylinders I moved the timing from 24 to 28 with little change. It runs pretty good otherwise. The aircraft is a 1965 Champion 7ECA. The air box is smaller than that of a cessna 150, I have thought about installing a 150 air box and testing to see if that helps. I find it hard to believe that all cessna 150's run this way. It is very noticeable on takeoff, has a light stumble right at the last bit of throttle travel. Pulling it back to 85% or so cleans it back up. I have read about the idea that the carb adds extra fuel at full throttle for "cooling", if I thought there was some sort of passage in the carb that provided this extra fuel, I would pound some sort of plug in it and be on my way. I would think this would show up on a flow bench.
    Sounds to me that if it runs better with carb heat on or with the filter on that it's running too lean not too rich?

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

  10. #50

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    Quote Originally Posted by cubdriver2 View Post
    Sounds to me that if it runs better with carb heat on or with the filter on that it's running too lean not too rich?

    Glenn
    If your climbing and go to full throttle it will drop rpm, if you then lean with the mixture, you get the rpm back.

  11. #51
    fobjob's Avatar
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    Are you sure it's not an early one-piece venturi? Too rough to be airworthy....IMHO

  12. #52

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    I think your experiencing the conditions I outlined in post #38. The last 1/2" of throttle movement (towards full throttle) allows extra fuel flow for cooling and then you pull it back 1/2" for cruising. My MA-3 SPA has this "back suction economizer system", but not all have it....seems to me like yours does.
    If you have Precision Airmotives' PDF on MSA float carb handbook look in section 3 operations Item "F" then have a look at figure 2 to see it.

    Google precision airmotives msa handbook
    Last edited by Pacerfgoe; 11-23-2017 at 12:29 AM.
    Thanks Bill Rusk thanked for this post

  13. #53

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    An update to my problems, O-200A in Champion 7ECA, stumbling at WOT / rpm loss. Continued to try many things with no success. Replaced the Brackett air filter with a Donaldson P10-7150 ($98.75). Now, aircraft runs and SOUNDS much, much better. No more stumbling at full throttle. Bigger rpm drop in flight with carb heat, more ground static rpm.
    Likes Hardtailjohn liked this post

  14. #54
    zenairdave's Avatar
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    Quote Originally Posted by mk.temp View Post
    An update to my problems, O-200A in Champion 7ECA, stumbling at WOT / rpm loss. Continued to try many things with no success. Replaced the Brackett air filter with a Donaldson P10-7150 ($98.75). Now, aircraft runs and SOUNDS much, much better. No more stumbling at full throttle. Bigger rpm drop in flight with carb heat, more ground static rpm.
    Thanks for the update on your solution. I have just been avoiding full throttle position. One of my thoughts is I know my O200 is over propped with a 71-44 which is more likely a good C90 prop. Over propping makes a rich running engine and that maybe I should have a C90 carb on my O200. I have not spent the money to test my theory. I may test your different filter idea.

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