IowaRV9Dreamer
Well Known Member
I need some help from a Lycoming guru. I have an O-235-L2C engine with a stock carb, stock mags. Just installed multichannel EGT/CHT and I see something interesting:
At cruse (75% power) I can lean to peak EGT (#2) per Lycoming and I get very even EGTs & CHTs. All 4 EGTs are within 30-40 degrees. Engine runs smoothly. Amazingly good, I thought!
But at full power, full rich I see a 150-200 degree difference in EGTs, with cylinders 3 & 4 (the back 2) both lower than the front two. The CHTs are also both lower for the back 2 cylinders. The engine has always run noticably rough at full power / full rich.
There are no problems with probes, etc. Compressions are all OK, timing is on spec, and I just set the valve lash.
I know that a 150 degree EGT difference is not unusual for a carb'ed engine, but what I think is weird is that this engine can operate in a very balanced manner at lower power / leaned, but is more out of kilter at full power.
Does anyone have an idea what might cause this? I know it might not be fixable, but it seems like at full power / full rich (like in a climb) the back 2 cylinders aren't making as much power as the front 2. This would explain the roughness. I could sure use a bit more power, especially when climing at 300 fpm on a hot day
Thanks for any insight. My next test is to climb up high (8500, that will take a while) where I can try full power (full throttle) and lean to peak EGT and see if the EGTs level out. In other words, is the carb throttle plate causing the problem.
At cruse (75% power) I can lean to peak EGT (#2) per Lycoming and I get very even EGTs & CHTs. All 4 EGTs are within 30-40 degrees. Engine runs smoothly. Amazingly good, I thought!
But at full power, full rich I see a 150-200 degree difference in EGTs, with cylinders 3 & 4 (the back 2) both lower than the front two. The CHTs are also both lower for the back 2 cylinders. The engine has always run noticably rough at full power / full rich.
There are no problems with probes, etc. Compressions are all OK, timing is on spec, and I just set the valve lash.
I know that a 150 degree EGT difference is not unusual for a carb'ed engine, but what I think is weird is that this engine can operate in a very balanced manner at lower power / leaned, but is more out of kilter at full power.
Does anyone have an idea what might cause this? I know it might not be fixable, but it seems like at full power / full rich (like in a climb) the back 2 cylinders aren't making as much power as the front 2. This would explain the roughness. I could sure use a bit more power, especially when climing at 300 fpm on a hot day
Thanks for any insight. My next test is to climb up high (8500, that will take a while) where I can try full power (full throttle) and lean to peak EGT and see if the EGTs level out. In other words, is the carb throttle plate causing the problem.