Farmboy
MEMBER
Middlebury, VT
Cruiser and I were talking about this the other day, and so I thought I'd pose some questions here as I couldn't find specific prior discussion.
He can correct me on his O-320, but I believe he was saying he did not see an RPM drop when he pulled carb heat. His thought was that it was related to lack of good hot air feeding his carb when carb heat was applied.
On my O-290, I don't see a RPM drop either, but I know I have good heat, as the same muffler and flow will bake the cockpit. But, what I do see is an immediate rise in the EGT's when the carb heat is applied.
So originally I thought okay it's working, but then I realized that it's backwards. With carb heat applied, initial EGT response should be to go down due to a richer condition. An EGT rise makes me think it's getting leaner.... which in theory would only be possible if the mixture was already lean of peak? Is that theory correct, or am I backwards on this?
In flight by leaning the engine I can bring CHT's up to 350-370 degrees and have the appearance of a good burn. By richening the mixture up the CHT's will go back down from that. But... without an RPM drop with carb heat applied, and with EGT's that rise instantly with carb heat application.... seems like it's running lean to begin with.
Thoughts?
Thanks,
pb
He can correct me on his O-320, but I believe he was saying he did not see an RPM drop when he pulled carb heat. His thought was that it was related to lack of good hot air feeding his carb when carb heat was applied.
On my O-290, I don't see a RPM drop either, but I know I have good heat, as the same muffler and flow will bake the cockpit. But, what I do see is an immediate rise in the EGT's when the carb heat is applied.
So originally I thought okay it's working, but then I realized that it's backwards. With carb heat applied, initial EGT response should be to go down due to a richer condition. An EGT rise makes me think it's getting leaner.... which in theory would only be possible if the mixture was already lean of peak? Is that theory correct, or am I backwards on this?
In flight by leaning the engine I can bring CHT's up to 350-370 degrees and have the appearance of a good burn. By richening the mixture up the CHT's will go back down from that. But... without an RPM drop with carb heat applied, and with EGT's that rise instantly with carb heat application.... seems like it's running lean to begin with.
Thoughts?
Thanks,
pb