Hi all,
I have come to believe that my carb is a bit on the lean side, and am looking for someone to double-check my reasoning and lend any advice. I have an O-320-E3D (150HP), that has the 5130 carb, which is supposedly already the richer carb.
On takeoff, I am only seeing a max of about 11 GPM. This is at about 2250RPM and 29.5" MAP. I have a FP prop. The Lycoming charts suggest I should be a little over 12 GPM at these numbers. I am also noting slightly high CHT's on full-throttle climb out, and usually ease off the power around 1000' to keep them under 400. I understand there is nothing wrong with a bit over 400 in climb (it is 85* in FL today though), but I know it is possible to keep them lower.
To confirm my suspicions I did a lean test today at 8000' DA and 75% (full throttle). I found that my rear cylinders were plenty rich (>200* ROP at full rich), but the front cylinders only 60-80* ROP. This makes sense given the orientation of the carb butterfly valve directing more fuel straight up to the rear cylinders.
I have spent a lot of time on my baffles, and they pass the light test, as well as keeping things very cool in cruise. I have also checked that throttle and mixture arms are hitting the stops. I have looked for evidence of an intake leak and found none.
So, it is apparent that part of the problem is the poor distribution inherent in carbureted engines, but I would still like to see book numbers for fuel flow on takeoff. The guy who rebuilt my carb knows his stuff, but will only do certified work, so would not entertain a discussion about drilling or replacing the jet. He is however interested in learning more about the issue.
I am not opposed to drilling or replacing the jet, but as it is a critical part, would rather have a pro do it. Any input from the experts? Thanks!
Chris
I have come to believe that my carb is a bit on the lean side, and am looking for someone to double-check my reasoning and lend any advice. I have an O-320-E3D (150HP), that has the 5130 carb, which is supposedly already the richer carb.
On takeoff, I am only seeing a max of about 11 GPM. This is at about 2250RPM and 29.5" MAP. I have a FP prop. The Lycoming charts suggest I should be a little over 12 GPM at these numbers. I am also noting slightly high CHT's on full-throttle climb out, and usually ease off the power around 1000' to keep them under 400. I understand there is nothing wrong with a bit over 400 in climb (it is 85* in FL today though), but I know it is possible to keep them lower.
To confirm my suspicions I did a lean test today at 8000' DA and 75% (full throttle). I found that my rear cylinders were plenty rich (>200* ROP at full rich), but the front cylinders only 60-80* ROP. This makes sense given the orientation of the carb butterfly valve directing more fuel straight up to the rear cylinders.
I have spent a lot of time on my baffles, and they pass the light test, as well as keeping things very cool in cruise. I have also checked that throttle and mixture arms are hitting the stops. I have looked for evidence of an intake leak and found none.
So, it is apparent that part of the problem is the poor distribution inherent in carbureted engines, but I would still like to see book numbers for fuel flow on takeoff. The guy who rebuilt my carb knows his stuff, but will only do certified work, so would not entertain a discussion about drilling or replacing the jet. He is however interested in learning more about the issue.
I am not opposed to drilling or replacing the jet, but as it is a critical part, would rather have a pro do it. Any input from the experts? Thanks!
Chris