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Thread: Trouble shooters?

  1. #1

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    Trouble shooters?

    I have a problem that we can not figure out! I have a SC 150 with Penn Yan overhauled motor with 500 hours on it. I bought it with 220. Since then it has never ran to the rpm that prop manufactures say it should. Sen 74/56. Full throttle level flight 2500 rpms max. Borer 82-44 2600 max rpm straight and level with 2400 rpm climb out. So we put a new carb on and full At Lee dodge exhaust with hot rod muffler and went from generator to a new alternator. Checked mags. normal drop and timed right. Now it has less power than before. Very doggy specially at low rpms. Messed with idle mixture and got it flyable. But still very doggy, not peppy at all. In the process of doing this we found a broken primer line that we fixed and the throttle cable was not anchored so it was giving different throttle responses. We figure that was probably the main problem. But to no avail! Has anyone ran into this problem? Adjusting the idle mixture helped some. But per the carb manufacture it says its not effective over 1400 rpms. It sounds like it is flooded but no real signs of it being to rich. It runs like a old diesel truck. Very sluggish. Any advice would be appreciated?

    Thanks Scott

  2. #2

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    Air filter?


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  3. #3

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    Brand new air-filter.

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    What kind of mags? Did you check internal timing? Was this a new/rebuilt carb or just different one? What is the RPM drop with carb heat at 2400 RPM? How many degrees of EGT can you lean before you get peak EGT? Did you do a resistor check on the plugs? Do you have a 4 cylinder EGT/CHT?
    denny

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    Bendix mags. Just checked timing. They have about 550 hours on them. It is a new rebuilt carb from Avstar. At 1800 drops 80-100. did do a mag test in a climb under full power 2400 rpms. The same about 80 and engine run smooth. No resistor check on plugs. About 50 hours on new tempest plugs. No engine monitor. Was thinking on tying it to a tree and using a laser heat gun to check the exhaust pipes and see if I am getting same temps on each cylinder.

  6. #6
    cubpilot2's Avatar
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    Have you verified the accuracy of the tach. Sounds like your missing 100 -150 rpm.
    Common for a tach to be off that much.
    Ed
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  7. #7
    wireweinie's Avatar
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    Quote Originally Posted by scottsville View Post
    Bendix mags. Just checked timing. They have about 550 hours on them.
    Did you check the INTERNAL timing of each mag or just the timing of the mags to the engine? Then pull the plugs and measure the internal resistance of each one. What's the history of the plug leads? Out of the box or cut to length and hand terminated?

    Web
    Life's tough . . . wear a cup.

  8. #8

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    Quote Originally Posted by cubpilot2 View Post
    Have you verified the accuracy of the tach. Sounds like your missing 100 -150 rpm.
    Common for a tach to be off that much.
    Yes last December at annual. It was right on. I have a 160 SC here and there is a huge huge difference in performance between them.

  9. #9

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    Did not check internal timing. Just timing. One was 25 and 26. Not sure on the plug leads. They look good. Was completely rebuilt in 2012

  10. #10

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    Flat cam?
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  11. #11
    Tim's Avatar
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    Try leaning it a little on takeoff, might be a little rich



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  12. #12
    ADK_Cub's Avatar
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    Or cam timing. My 0-320 just came back from overhaul and it ran very similar to what your describing (like ****)

    First give away was not making peak RPM. Second was it was a little “poppy” or “snarky” when pulling the throttle back from full to idle.

    Engine shop had the cam timing one tooth off on the cam gears.


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  13. #13

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    I'd buy a new exhaust.

  14. #14

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    I have new exhaust. I did do a run up at 1500 rpms and check temps on exhaust pipe right out of cylinders. all ran in the low 500's and one ran in the low 600's. Maybe not getting enough fuel in that cylinder?

  15. #15

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    Is anyone have trouble getting to 2700 rpms with a 0320 150 at straight and level flight with a borer 82-44 prop? My understanding it should have no issue hitting 2700 even in a shallow climb?

  16. #16
    www.SkupTech.com mike mcs repair's Avatar
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    compression check? leaky/sticky/bent intake valve will effect more than just that cylinder.....

  17. #17

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    BTW. Static rpm was 2250 rpms. Has anyone did that test with a 150 with borer 82-44? Sounds low to me.

  18. #18

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    Compressions were 78-77-78-74. and the 74 is the cylinder that the temps were over 100 degrees hotter than the rest

  19. #19

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    I was being a smartass since you're asking the same questions you asked 2 weeks ago.

    44 pitch is a lot for 150 hp. When I had a fresh 160hp and a brand new prop 8242 netted 2700 in low altitude level flight.
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  20. #20

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    Quote Originally Posted by stewartb View Post
    I was being a smartass since you're asking the same questions you asked 2 weeks ago.

    44 pitch is a lot for 150 hp. When I had a fresh 160hp and a brand new prop 8242 netted 2700 in low altitude level flight.


    Since I asked that question I replace the exhaust and carburetor. The old exhaust was really messed up inside. All the new exhaust and new carb did was make it worse. Borer prop stc shows that a Sc 150 should min produce 2300-2400 static rpms with a 82-44. I have friend thats had over 6 150 SC and he never had a problem redlining a 82-44

  21. #21

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    I had a stock Sen 74-56 on it before and Don at Sensenich said I should get 2700 rpms no problem with that prop on a 150. and never saw over 2500 rpms.

  22. #22

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    https://www.aircraftspruce.com/catal...es/trutach.php

    Does anyone you know have access to one of these? It's a good double check on your tach accuracy.

    If the mags have not been removed and inspected for e-gap/internal timing in 500+ hours, I would start there.

  23. #23
    AkPA/18's Avatar
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    Quote Originally Posted by scottsville View Post
    Since I asked that question I replace the exhaust and carburetor. The old exhaust was really messed up inside. All the new exhaust and new carb did was make it worse. Borer prop stc shows that a Sc 150 should min produce 2300-2400 static rpms with a 82-44. I have friend thats had over 6 150 SC and he never had a problem redlining a 82-44
    I am unclear exactly what was made worse but I have a hard time believing a new exhaust would be the culprit. I have always been leary of new carbs.
    Edit. It sounds like your exhaust was really messed up inside. It could possibly been the problem and previous carb was ok and new one could have issues? It is tuff sometimes to diagnose when more than one change is done. Good luck with your issues.
    Last edited by AkPA/18; 10-12-2020 at 12:59 PM.
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  24. #24
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    Quote Originally Posted by scottsville View Post
    I have a problem that we can not figure out! I have a SC 150 with Penn Yan overhauled motor with 500 hours on it. I bought it with 220. Since then it has never ran to the rpm that prop manufactures say it should. Sen 74/56. Full throttle level flight 2500 rpms max. Borer 82-44 2600 max rpm straight and level with 2400 rpm climb out. So we put a new carb on and full At Lee dodge exhaust with hot rod muffler and went from generator to a new alternator. Checked mags. normal drop and timed right. Now it has less power than before. Very doggy specially at low rpms. Messed with idle mixture and got it flyable. But still very doggy, not peppy at all. In the process of doing this we found a broken primer line that we fixed and the throttle cable was not anchored so it was giving different throttle responses. We figure that was probably the main problem. But to no avail! Has anyone ran into this problem? Adjusting the idle mixture helped some. But per the carb manufacture it says its not effective over 1400 rpms. It sounds like it is flooded but no real signs of it being to rich. It runs like a old diesel truck. Very sluggish. Any advice would be appreciated?

    Thanks Scott
    Altitude?

    Have you confirmed that the throttle linkage is allowing full travel on the carb?

    Where are you located?

    9/10 it is something simple.

    Tim

  25. #25

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    We ran a spectrum on the the motor in December and the rpm was right on. Engine showed it ran very smooth. better than average. The throttle linkage it good. hits full stop

    I wanted to change each item and then fly it But the generator hit the new exhaust so we went ahead and put a alternator on it. So that caused us to have to replace all of it at once.

  26. #26

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    What altitude are you at?
    DENNY

  27. #27

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    1330 msl

  28. #28

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    If you still have the old Carb I’d put it back on and see what that does.

  29. #29
    www.SkupTech.com mike mcs repair's Avatar
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    On hot cylinder, look for induction leak, broken gasket, loose tube going into sump(you have to reswage tube to tighten)

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    BC12D-4-85's Avatar
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    What condition made you feel the old exhaust was "messed up" compared with the new one? What exhaust did you have before and then now? For example a freer flowing exhaust can create a leaner fuel mixture in some engines. Lean mixtures can lead to light tan to white colored exhaust stains inside the muffler outlet. Too rich and they are dark tan to black. Same for spark plugs.

    Gary
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  31. #31
    algonquin's Avatar
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    Scott my best advise is to sit down and make a list of everything that is being discussed and go Thur them one at a time and make notes. That way you won’t be shotgunning .
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  32. #32

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    Update: Checked for induction leaks with WD40 running and no sign on the engine sound. Did a static pull test and got barley 2250 rpms. Borer 82-44 stc states min of 2300. But did order all new gaskets and intake hose. Also going to send mags off to get 500 hr check. Also been talking with avstar on the new carb. Hopefully they can give me some input. It feels like it is flooded. Very old diesel pick up feeling power. But the guys that I have talked to that have huge experience are saying it sounds lean to them. I have tested at higher rpm on leaning the mixture to see if I can get a rpm rise. But it does not. if the new induction gaskets and hoses and rebuilt mags do not do the trick. I think we will check on fuel flow and start checking cam lobe wear etc... Motor runs smooth and nice. Just no power!

  33. #33
    BC12D-4-85's Avatar
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    Maybe asked and answered already but does adding carb heat = richer mixture help or hurt rpm?

    Gary
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  34. #34

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    Already mentioned but 82-44 is too much prop for a 150 hp.
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  35. #35
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    Have you checked the damper in the airbox? If it's sloppy and not fitting tight, so
    It won't move back when you push on it??
    Doesn't take much to start blending "hot air" into your carb....... That combined with
    44" of pitch would do just what your saying it does.

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  36. #36
    PerryB's Avatar
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    Whats the compression ratio? If it's truly a 150 w/ 7:1 compression, your numbers are in line. Those are a couple of highly pitched pitched props. For such an application, the Borer could stand to lose 2" of pitch, and the Sens. about 3".
    Last edited by PerryB; 10-16-2020 at 06:36 AM.
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  37. #37

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    I have a friend that has had 7 SC 150's over the years and he always ran 82-44 on them and he said he never had a issue running them up to 2800 rpms straight and level flight. The Borer STC states min rpm out of a 150 is 2300 to 2400. I am barley getting 2250. Don a Sensenich says you should have no issue hitting 2700 rpm in straight and level flight with the 74-56 sen prop. I might be able to hit 2500 on a good day. I have a Buddys SC 160 with a borer 82-42. which is 2 deg flatter than mine. and 10 hp difference. It takes off over twice as fast as mine. I've flown it a bunch. There is a huge huge difference in them. I believe there should be a pretty big difference between them. but not over twice as much?
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  38. #38

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    Your friend must have had bad tachs. Put an 82-41 on your plane and you'll be smiling. 82-42 might work but if you're using a Borer you might want to take advantage of what they do when pitched correctly.
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  39. #39

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    I hear ya on taking advantage of the borer. That is the hole idea.
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  40. #40

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    I have heard that every degree of pitch is about 50 rpms? Is this correct?

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