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Thread: Does it matter?

  1. #1

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    Default Does it matter?

    1956 PA22-150. Throttle cable was stiff. Removed to clean and lubricate. A week or two passed between the remove and replace. Did not note and do not remember which position on the carb lever it was originally positioned. Reinstalled on the middle position. Does it matter which of the three holes on the carb lever the throttle cable is connected?

  2. #2
    Stephen's Avatar
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    Default Re: Does it matter?

    Make sure that the throttle hits both stops on the carburetor just before you run out of throttle travel. Find the hole that allows sufficient throttle travel and hits the stops. Mine is in the middle hole.
    "You can only tie the record for flying low."

  3. #3
    Vagabondblues's Avatar
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    Default Re: Does it matter?

    The three holes are for adjusting the stroke of the acceleration pump. The outermost hole no.3 has the greatest throw and causes the accelerating pump to deliver the most fuel when the throttle is advanced rapidly. Middle hole no.2 is the standard accelerate pump position and no.1 the most inward provides the least stroke. As you advance the throttle rapidly the accel pump atomizes fuel into the Venturi to make up for the lack of pressure differences at the discharge nozzle. If the engine hesitates or stumbles when accelerating you adjust the hole up in numbers.

  4. #4
    Administrator Steve Pierce's Avatar
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    Default Re: Does it matter?

    Quote Originally Posted by Vagabondblues View Post
    The three holes are for adjusting the stroke of the acceleration pump. The outermost hole no.3 has the greatest throw and causes the accelerating pump to deliver the most fuel when the throttle is advanced rapidly. Middle hole no.2 is the standard accelerate pump position and no.1 the most inward provides the least stroke. As you advance the throttle rapidly the accel pump atomizes fuel into the Venturi to make up for the lack of pressure differences at the discharge nozzle. If the engine hesitates or stumbles when accelerating you adjust the hole up in numbers.
    I have always set the throttle lever to go stop to stop and if need which has been rare adjust the accelerator pump linkage accordingly.
    IMG_20190610_071001.jpgIMG_20190610_071109.jpg

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  5. #5

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    Default Re: Does it matter?

    Thank you all for your replies. There is more to the story. My brother and I bought the Tripacer a little over a year ago. It came from out in West Texas. We had a buddy pilot ferry it from Texas to Virginia. Un-eventfrul flight. Due to the installation of two stents (in me, not the tripacer), it has been a while since I have been able to fly it. Got 3rd class reinstated via the usual hoop jumping. The cleaning of the throttle cable did not resolve the stiffness issue. Replaced cable with the expensive Univair cable. Positioned in middle hole. It was time for it's annual so another month passes. Annual completed, time to fly with instructor. Run-up and mag check at 1800 RPM was fine. Engine very smooth running. Seemed a bit down on power, aborted take-off. Max RPM of 2100. Back into the hanger. Pulling out hair to figure out problem. Have done the obvious stuff. Checked throttle lever motion (its going stop to stop). Checked timing, checked fuel flow on left tank by disconnecting hose from carb and into 5 gal gas can (5gal=6min), eight new Tempest 37 plugs recommended on this site. Higher static of 2300 RPM with new plugs so I flew it. Still seems down on power. It has a 72 1/2x61 prop as noted from logs. Best rpm at full throttle and 115 mph was 2500. CBE is at about 800 ft asl. Stayed in pattern so did not lean. Carb heat makes it run really rough. Did not lean for best RPM on takeoff. Is my problem my flight technique or is there a problem with my engine. Should I be needing to lean for best RPM on takeoff at 800 absl. Not a hot muggy day with high DA.

  6. #6
    Administrator Steve Pierce's Avatar
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    Default Re: Does it matter?

    A 61" prop is pretty anemic in static and climb. I had one and thought it was sick until I bolted a 58" on it. You make minimum static rpm per the Type Certificate.

  7. #7

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    Default Re: Does it matter?

    I was starting to wonder about the prop. I was hoping the shorter 72.5 x 61 would equal the recommended 74x58. Does anybody near VA have an extra prop that I could try before sending mine to the prop shop or one for sale? I suspect re-pitching mine would be the least expensive route to go.

  8. #8

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    Default Re: Does it matter?

    Per the TCDS, length not less than 72.5”, static RPM not less than 2250 RPM. First thing to check is your tach as mechanical tachs are known to have significant variations. Next would be to check idle mixture. Since you are at 800’msl, if it’s hot your DA will be somewhat higher. It wouldn’t hurt to lean for best power on the ground and see what you get.

    Just remember, everything is a compromise, you can re-pitch to a flatter pitch. That helps TO and climb, but you loose on cruise. It all depends on what you are using the airplane for. If you always operate from long paved runways, leave it as is. If you will be going in and out of short strips, having more of a climb prop helps. When I had my PA-22-160, I was running a 54” pitch prop, but would see 2700 RPM at 80 mph in the climb with full throttle. That said, I used to operate out of lots of strips less than 700’ and I was using it to tow banners.


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  9. #9
    Wag-builder's Avatar
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    Default Re: Does it matter?

    Hey Steve,

    I am in southern Maryland at 140' MSL with a 150 hp O-320 with a 74 x 61 prop and turn 2300 static RPM and with full fule and two adults I climb at about 1000 FPM on a 80 degree day. I usually cruise at 2300 RPM and 115 mph and 7.2 GPH full burn leaned. I do not have wheel pants on my plane and I don't have anything extra either, so I am about as light as I can be.

    Steve

  10. #10
    Gilbert Pierce's Avatar
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    Default Re: Does it matter?

    My first action would be to lean on the ground.

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