High CHT, w/o getting full power

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    • May 7, 2020 at 00:24 #13747
      Jeff Anderson
      Participant

      Bought 77 Cheetah Recently which has Westach CHT gauge in it. Only one cylinder (#3) was hooked up.

      As part of pre-buy, replaced all the plugs, bUt in test flights it was not making full power, about 2350 RPM at 600 feet elevation. Compression tests all indicated 70 psi or better. Baffling looked in ok shape above, but nose bowl was not taken off.

      Oil temp high on flight home. Fresh annual when I got it home. Passed with flying colors, to include flushing oil cooler and getting fresh wire harness and probes to all cylinders. High compression cylinder STC on this rebuild.

      Present situation, RPM has not significantly improved, and with short flights, 3 cylinders are indicating 500 degrees, running full rich. Oil temp is back in the green, just north of midrange. When I pull power cylinders immediately cool off.

      Mechanic believed it was a mixture issue in the carburetor. We pulled that and sent it out for bench test. Flow is right down the middle where it should be, but shop said this carb had been modified via a SB in the 80s to run lean. Has anyone heard of this? This would seem to account for high CHT and not producing full power.

      Only issue is previous owner said he had no problem getting 2650 RPM out of it and no high CHT on cylinder that was hooked up?

      Any ideas I would appreciate!

    • May 7, 2020 at 12:27 #13748
      Roscoe Rosché
      Keymaster

      Okay, you did the cylinders, carb now being redone for richen mixture, that leaves the mags. Where are they in the 500 hour inspection and where are they timed? Low timimg makes for elevated temps and low power.

      FYI

      Roscoe

    • May 7, 2020 at 16:46 #13749
      Jeff Anderson
      Participant

      Thanks Roscoe. They are at 25 degrees BTC having been recently checked on the annual. I’m asking my mechanic to look at the condition of the baffling surrounding lower lower cowl for leaks.

    • May 24, 2020 at 13:36 #13846
      Dennis DeWitt King
      Participant

      New to this site. I have owned my current Cheetah since 2007; with high compression upgrade. Have fought high cylinder temps on takeoff forever. I finally found 2 things that completely fixed the problem.
      1. I got the carb rebuilt and richened with bigger jets. The folks at D&G supply in Michigan are experts on getting you the right carb setup for HC Cheetahs. This helped keep temps lower.
      Telephone: 269-684-4440

      2. Install a “Candeletti” cowl flap just forward of the cowling cooling exits underneath. They bend down 45 degrees and create a low pressure area that sucks more air out the bottom of the airplane. I fabricated two pieces of aluminum and bolted them on. It makes a HUGE difference. Peak cylinder temps on takeoff came down 30-50 degrees. I have attached a drawing.

      Deflector

      With these two mods I can fly my Cheetah here in Florida in the summer and keep my peak temps easily below my personal limit of 450 degrees, usually under 410 or so.

      Call me any time if you have questions; 801-918-9722.

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    • May 24, 2020 at 16:21 #13849
      Roscoe Rosché
      Keymaster

      This is why I send all my carbs to Russ at D&G. Most time they require no adjustment.

    • May 24, 2020 at 22:29 #13853
      Jeff Anderson
      Participant

      Thank you Dennis and Roscoe! I am getting a rebuilt carburetor as per your suggestions. Dennis, I might reach out to you on that cowl flap. Sounds like that is just the mod I need. I’m at 615-275-7962. Appreciate all the input!

    • May 26, 2020 at 18:38 #13867
      Robert Laskin
      Participant

      check internal mag timing (E Gap) 500 degrees @ 2350 RPM something waaay wrong carb rigging? hitting max stop? correct spark plugs and gaps? proper mag drop?

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