dkallen
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- Apr 21, 2010
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My cherokee is a 1969 180 Model D with the O-360-A4A engine. I have always suspeced that I had a bit of a miture problem, but it appears that it may actually be a fuel flow issue. Just wondering if any of you have a fuel flow unit on your Cherokee. According to the Lycoming manual, the fuel flow at 28.5 inHg manifold pressure should be about 17.5 GPH according to the performance graph for maximum power. On the Power Curve, it shows a specific fuel flow of 0.55 lb/BHp/hr which would be approx 16.5 GPH. At 28.5 inHg, I am getting a maximum flow of 15.1 GPH. It looks like this is causing my #3 cylider to be a little lean and has a temperature profile different than the other 3 cylinders. It is getting hot to the tune of >400F on climbout and it went to 440 before I arrested the heatup by pulling back the power (I was already full rich).
I have always suspected a fuel distribution issue because #4 was always coolest and #3 was always hottest. I found a couple of issues that I would have expected to resolve the #3 problem, but none worked. The issues resolved included gaps in the affling, a large gap above the oil cooler and a concern about the air side pressure drop across the oil cooler, so I replaced the oil cooler also. It is looking like the root of the problem is due to a lack of cooling due to fuel flow. This annual, we found a small restriction to exhaust flow and replaced the exhast system. Also due to cleanig up the airframe and the potential of overspeeding the prop, I went ahead and had the prop re-pitched and this wound up agrivating the #3 CHT issue.
So I am asking if anyone knows what the maximum fuel flow through carb at full rich is suppose to be?
I have always suspected a fuel distribution issue because #4 was always coolest and #3 was always hottest. I found a couple of issues that I would have expected to resolve the #3 problem, but none worked. The issues resolved included gaps in the affling, a large gap above the oil cooler and a concern about the air side pressure drop across the oil cooler, so I replaced the oil cooler also. It is looking like the root of the problem is due to a lack of cooling due to fuel flow. This annual, we found a small restriction to exhaust flow and replaced the exhast system. Also due to cleanig up the airframe and the potential of overspeeding the prop, I went ahead and had the prop re-pitched and this wound up agrivating the #3 CHT issue.
So I am asking if anyone knows what the maximum fuel flow through carb at full rich is suppose to be?
