When in cruise mode leaned out to about 8.8 gallons per hour 6K feet the EGT spread is about 130 degrees between the high and low exhaust. The conditions are not classic for carb ice. Pull the carb heat on and the spread goes down to 80 degrees. With the carb heat off the spread goes to 90-100 and remains there. The temps does not climb back to a 130 differential. Can somebody please explain to me. Thank you
EGT spreads
- Thread starter Skipper
- Start date
belloypilot
Active Member
Not really enough information to provide much in the way of useful feedback. EGT spreads don’t really mean that much because probe placement can make a huge difference. What matters is, at a given power setting, what fuel flow each EGT reaches peak temperature. Start well rich of peak and gradually lean and watch each EGT, noting the exact fuel flow where each cylinder peaks. The fuel flow difference between the first and last cylinders to peak is a useful basis for comparison if troubleshooting fuel/air ratio issue. The specific temperature values are less useful.
As for your carb heat on/off observation, when carb heat is on the mixture is richer than with it off. If cycling the carb heat doesn’t return EGTs to their original temperatures that indicates you aren’t returning to the previous F/A ratios (either that or your power settings have changed). Perhaps after cycling the carb heat the damper isn’t fully closing and you are getting a bit of warmer air and richer mixture as a result? Just a wild ass guess but verifiable if you have a carb temperature probe.
Keep us posted what you come up with.
As for your carb heat on/off observation, when carb heat is on the mixture is richer than with it off. If cycling the carb heat doesn’t return EGTs to their original temperatures that indicates you aren’t returning to the previous F/A ratios (either that or your power settings have changed). Perhaps after cycling the carb heat the damper isn’t fully closing and you are getting a bit of warmer air and richer mixture as a result? Just a wild ass guess but verifiable if you have a carb temperature probe.
Keep us posted what you come up with.
Snowbirdxx
Well-Known Member
Check how your cab heat cable / wire is attached to the butterfy arm in the airbox. Airbox should be closed with the carb heat pulled 1/2 inch. Then, when you press the carb heat fully in, you are preloading the butterfly and that prevents vibration, which wears the bearings.