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Thread: Building an Experimental PA11

  1. #281

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    I could only get 2200 static with the 76AK. That’s 100 less than the Catto

  2. #282
    BC12D-4-85's Avatar
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    Quote Originally Posted by Dan Gervae View Post
    I could only get 2200 static with the 76AK. That’s 100 less than the Catto
    Please try w/o the air filter as well. The cam and ignition timing of the O-200 is different than for a C-90....made more for higher rpm horsepower with short C-150 prop, I suspect. Specs are in the overhaul manual for each. C-90 max rated 90 hp at 2475; 95 hp at 2625 5 min. O-200 100 hp @ 2750, etc. You have a C-90 on the "T". What's the static on that with that prop?

    However, JimC used to report good things about the O-200's here and elsewhere. He developed a graph that I have that showed the O-200 mo betta' at all rpms. Guess it all depends on prop-carb-ignition timing-compression-cam-intake-exhaust. The Piper exhaust may be more restrictive than say a C-150 exhaust for example. Same for air filters.

    Gary
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  3. #283
    BC12D-4-85's Avatar
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    Make sure your carb heat is fully off and flapper leakage minimal. Make sure your throttle throw is fully open. Confirm magneto timing is correct. Try static w and w/o air filter. Compare static to your C-90 as mentioned. It would also be nice to confirm compression and check if valve timing and lift is per specs with a degree wheel on the crank. In other words make sure the O-200 is sound before chasing props. The C-90's are a torquey engine. The intake valve closes a few degrees earlier than the O-200 which helps some.

    Gary

  4. #284

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    Same result without air filter. Anyone know the best setup for a Marvel carb on an O-200? Like a start point and then fine tune. The idle mixture may be slightly rich as I occasionally get a stumble on takeoff...usually on a touch and go or full stop and then go again....any pointers on optimizing this?

    compressions are 77,78,78,76
    timing is 24 degrees (old serial number cylinders).
    engine has 300 Ish hrs on top and 30 on lower (new bearings after tear down and internals magnafluxed and yellow tagged) I can get over 2800 on full throttle in cruise.

  5. #285
    cubdriver2's Avatar
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    0200 is like a 2 stroke bike, needs to rev. I had a 7636 catto on my 0200 cub and got about what you got. The 7440 1b90 was worse, my stroker will turn the Mac 2550 on takeoff

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  6. #286
    cubdriver2's Avatar
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    Quote Originally Posted by Dan Gervae View Post
    Same result without air filter. Anyone know the best setup for a Marvel carb on an O-200? Like a start point and then fine tune. The idle mixture may be slightly rich as I occasionally get a stumble on takeoff...usually on a touch and go or full stop and then go again....any pointers on optimizing this?

    compressions are 77,78,78,76
    timing is 24 degrees (old serial number cylinders).
    engine has 300 Ish hrs on top and 30 on lower (new bearings after tear down and internals magnafluxed and yellow tagged) I can get over 2800 on full throttle in cruise.
    Stumble sounds lean?

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

  7. #287
    BC12D-4-85's Avatar
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    Best to compare the C-90 to O-200's performance with that AK76 prop.

    Accelerator pump has three adjustments. See MA-3-SPA Manual for troubleshooting and options. Page 2-3 and Fig. 4.

    Edit: Install a manifold pressure gauge. Note the indicated ambient pressure prior to takeoff. Note it WFO near the ground as safe. Should be close like within 2" or even less if the engine's volumetrically efficient. Note at idle. Should be low around 10"+- if the engine is tight internally and intake leak-free. Also good for setting power and detecting carb ice early.

    Gary
    Last edited by BC12D-4-85; 06-08-2021 at 09:01 PM.

  8. #288

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    https://msacarbs.com/carburetor-troubleshooting/

    I feel like the Engine is fine...just need to turn it faster. I wasn’t surprised that the 76AK Was too much prop to spin fast. I would like to try the adjustable Sensenich....I wish I had bought one....at the time I was buying my Catto there was all that stuff about vibration/harmonics on an O-200...it was the 72” version then. The 76 adjustable sounds intriguing....but I could wrong. I love the ideas so far. I remember Glenn telling me a while back that he had not been happy with the 76-36 on his O200. I tried and seems like the same results he had. Nicole at Catto said you get 30-40 rpm per inch on static and 50-60 rpm per inch at max.....She can move it up to 3”...so the full 3” should get me 2390-2420 static and I’m thinking I’d gain 120-150 rpm on takeoff which would change my takeoff performance quite a bit
    Last edited by Dan Gervae; 06-08-2021 at 09:26 PM.

  9. #289
    BC12D-4-85's Avatar
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    The C-150 seaplane w/ O-200 swinging a 1A90/CF75-35-38 range wants to see 2400 to 2500 static. That Sen AK76-2-40 I can run 2440+-15 static with the Stroker and max just over 2600. Apples and fresh oranges of course. I'd consider the Sen adjustable.

    But.....If I had a Taylorcraft C-90 capable of speed and a PA-11 O-200 capable of STOL I might swap engines. You have a beautiful plane that you're figuring out what it's for and how it's going to be used. My PA-11-90 on floats flew upper 80's - lmaybe ow 90's at the same 2400 rpm and prop (AK76-2-40) as my Taylorcraft now goes over a hundred. Fun choices Dan.

    Edit: How about 8.5:1 pistons and cylinders to put some lead in that pencil?

    I was born in Escanaba and lived in the UP 14 yrs. Nice place.

    Gary
    Last edited by BC12D-4-85; 06-08-2021 at 11:15 PM.

  10. #290
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    If you haven't already done so, you might want to check the tachs for accuracy too.

  11. #291

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    Quote Originally Posted by supercrow View Post
    If you haven't already done so, you might want to check the tachs for accuracy too.
    good point. I’ll borrow my buddies digital tach. I ran a static check on the C90 with the 76AK-2-40 and it statics around 2300. That’s 100 more than the O200 will spin it. Provided either of my analog tachometers are accurate. I do know that the plane performs fine (for an electric equipped 840 lb cub)....it’s been in the 90s here the last few days with DA nearing 4000’ so early mornings are when I’ve been flying. I just know when I put this thing on floats I’ll need to get more RPMs on takeoff for sure. That won’t happen until next year, but I’d like to get it sorted out. Again, my mission starts to point towards. Ground adjustable. I’d sure like to try one out. Anyone out there running a stock O-200 with the Sensenich 76” ground adjustable? I’d like a pirep before I make such a purchase.
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  12. #292
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    Quote Originally Posted by Dan Gervae View Post
    ......so I can send my Catto for a re-pitch.......
    As I understand it, the Catto prop is wood with a composite covering.
    How do they repitch it?
    Cessna Skywagon-- accept no substitute!
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  13. #293

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    They remove material from one side and add to the other, then recoat as I understand it. That's as far as my understanding goes though. Appearently it is fairly easy.....But I would sure like to see it done just to satify my curiosty.
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  14. #294
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    Building an Experimental PA11

    Dan I’ve had two Sensenich 76” ground adjustable props, an early one on my C-90 (first of the new design) and then again on my O-290.
    Compared with the props used prior the C-90 took better advantage and really shined, but I was very happy with both, and would highly recommend it.

    On my C-90 it literally felt like I added 20-30 hp during the ground roll due to the rate of acceleration.

    Note : these two engines use two different props - the c85/90/o-200 uses a sq tip 76” and the o-290 was two blades from a 3-blade design that was more of a tapered ninja blade.
    Thanks Dan Gervae thanked for this post
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