netsurfr
Well-Known Member
- Joined
- Jun 15, 2014
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As many of you know I have a Dakota, and like other Dakota owners experienced high CHT's during takeoff climb at FT. But I seemed to have higher CHT's than other Dakota owners here where in my case I could see as many as 3 of my cylinders reach low 400s during takeoff climb. I could control the temps by easing back on the throttle and/or reducing IAS to induce more air flow into cowl and they would quickly drop below 400F so all was good. During cruise flight if I was running at say 70% HP I noticed I had to go much richer than other Dakota owners or POH in order to keep 1 cylinder (#5) from reaching 400F. I did all the common things to address/improve the cooling such as ensuring baffles were good, plugging in any small holes that could disturb the pressure differential and prevent air from flowing down through cylinders, ensuring engine timing, magnetos, sparks, harness, intake/exhaust leaks, and fuel flow were all checked and working correctly but after all that I still had this nagging issue but considering the temps were really not in any danger zone and everything in the engine checked out I opted to not let it bother me. The only OTHER item left that could affect CHT's was the carb so I've been meaning to have it checked as the last item that I could check so I sent it out for inspection last week....
Results... They found a "gouge" by the inlet jets that was allowing air into the carb and messing things up resulting basically in an always lean mixture so they overhauled the carb and I just got back from a test flight and let me tell you.... WOW!
First the CHT's were about 30F cooler across the board (hottest any 1 cylinder got was 384F and that was after purposedly idling on the ground 15 minutes before takeoff to let the engine get hot and climbing FT to 5K at 95 KIAS (high AOA)). Second, the differential EGT spread was much reduced than any time before. And third (and this was huge), there was a significantly reduction in vibration during all phases of flight but especially noticeable on the ground at low MP/RPMs. I didn't really have a vibration problem before (so I thought) BUT today it felt so smooth it was amazing. Almost as smooth as the Lance/Toga with their engines so far forward of the cabin that you hardly feel any vibrations from the engine in the cabin.
So moral of the story here is that if you're dealing with hot CHTs and have checked all the usual suspects, you may want to have your carb checked!
Results... They found a "gouge" by the inlet jets that was allowing air into the carb and messing things up resulting basically in an always lean mixture so they overhauled the carb and I just got back from a test flight and let me tell you.... WOW!
First the CHT's were about 30F cooler across the board (hottest any 1 cylinder got was 384F and that was after purposedly idling on the ground 15 minutes before takeoff to let the engine get hot and climbing FT to 5K at 95 KIAS (high AOA)). Second, the differential EGT spread was much reduced than any time before. And third (and this was huge), there was a significantly reduction in vibration during all phases of flight but especially noticeable on the ground at low MP/RPMs. I didn't really have a vibration problem before (so I thought) BUT today it felt so smooth it was amazing. Almost as smooth as the Lance/Toga with their engines so far forward of the cabin that you hardly feel any vibrations from the engine in the cabin.
So moral of the story here is that if you're dealing with hot CHTs and have checked all the usual suspects, you may want to have your carb checked!
