My RV6 is running a carbureted O360, stock, except for 9:1 pistons. Since I’ve owned the airplane I have suspected that the engine ran a bit lean. I’m hoping that one of you have experienced my symptoms, and can comment.
The carb is a M/S MA-4-5. When I first acquired the airplane, I decided to send the carb out for inspection. Mainly for peace of mind, since the airplane had not been flying, but also because upon shutdown, there was not the rise in RPM one would expect. Adjusting the mixture screw didn’t help. The shop said all was good, but they did drill out both the main and idle jets to proper specs, saying that was not unusual. This really didn’t affect the lack of rise on shutdown situation, but the engine ran well, so I didn’t worry much about it. I have unscrewed the idle mixture screw about as far as I dare (4 turns), but still no change. Further evidence of a lean condition became apparent when operating out of a high elevation airport. Taking off at 7,000’+ MSL, I would expect to have to lean a good bit in order to get maximum power from the engine, but leaning the mixture didn’t seem to have much effect.
I’ve downloaded flight data from the Dynon. It shows fuel flows to be around 12 gph late in the takeoff roll, and maybe getting up to around 13 gph while accelerating in the climb. (this is a fixed pitch propeller, so RPM changes w/ accel.) I haven’t calibrated the “Red Cube” fuel flow sender, just keeping the default settings, so I can’t be sure of its accuracy, but its other readings seem reasonable.
The other thing that occurs is roughness and about 150 RPM drop during run up when operating just on the electronic ignition, while the side with the mag showed the expected drop. It was suggested by Electroair that this, along with the lack of RPM rise at shutdown indicated a lean mixture, perhaps caused by an induction leak. Because of the otherwise smooth operation at low idle, I didn’t believe this was the case, but I tested for a leak using both a shop vac plugged into the inlet and soap bubbles, as well as spraying WD-40 around the carb and inlet pipes looking for an RPM change. Nothing indicated a leak. I decided to change out the intake gaskets anyway.
I spoke with the carburetor shop, and the guy clarified for me that the idle mixture setting has no affect on mixture once you are beyond about half throttle, and indicated that we may need to drill out both jets a bit more. I’ve pulled the carb, and am going to let them take a look at it next week.
My question is: Does this takeoff fuel flow look reasonable for an O-360 w/ 9:1 pistons and a fixed pitch prop? The data shows engine RPM at rotation (IAS 66.4 kts) was 2,300. Fuel flow, 11.9. Also, Is it common to have to be experimenting with jet sizing? He said that non-standard equipment, like a tuned exhaust will affect carburation, but I’ve got the same Vetterman 4 into 2 system that most RV’s sport, so I see nothing odd there. Anyway, I’d appreciate any inputs anyone might have.
The carb is a M/S MA-4-5. When I first acquired the airplane, I decided to send the carb out for inspection. Mainly for peace of mind, since the airplane had not been flying, but also because upon shutdown, there was not the rise in RPM one would expect. Adjusting the mixture screw didn’t help. The shop said all was good, but they did drill out both the main and idle jets to proper specs, saying that was not unusual. This really didn’t affect the lack of rise on shutdown situation, but the engine ran well, so I didn’t worry much about it. I have unscrewed the idle mixture screw about as far as I dare (4 turns), but still no change. Further evidence of a lean condition became apparent when operating out of a high elevation airport. Taking off at 7,000’+ MSL, I would expect to have to lean a good bit in order to get maximum power from the engine, but leaning the mixture didn’t seem to have much effect.
I’ve downloaded flight data from the Dynon. It shows fuel flows to be around 12 gph late in the takeoff roll, and maybe getting up to around 13 gph while accelerating in the climb. (this is a fixed pitch propeller, so RPM changes w/ accel.) I haven’t calibrated the “Red Cube” fuel flow sender, just keeping the default settings, so I can’t be sure of its accuracy, but its other readings seem reasonable.
The other thing that occurs is roughness and about 150 RPM drop during run up when operating just on the electronic ignition, while the side with the mag showed the expected drop. It was suggested by Electroair that this, along with the lack of RPM rise at shutdown indicated a lean mixture, perhaps caused by an induction leak. Because of the otherwise smooth operation at low idle, I didn’t believe this was the case, but I tested for a leak using both a shop vac plugged into the inlet and soap bubbles, as well as spraying WD-40 around the carb and inlet pipes looking for an RPM change. Nothing indicated a leak. I decided to change out the intake gaskets anyway.
I spoke with the carburetor shop, and the guy clarified for me that the idle mixture setting has no affect on mixture once you are beyond about half throttle, and indicated that we may need to drill out both jets a bit more. I’ve pulled the carb, and am going to let them take a look at it next week.
My question is: Does this takeoff fuel flow look reasonable for an O-360 w/ 9:1 pistons and a fixed pitch prop? The data shows engine RPM at rotation (IAS 66.4 kts) was 2,300. Fuel flow, 11.9. Also, Is it common to have to be experimenting with jet sizing? He said that non-standard equipment, like a tuned exhaust will affect carburation, but I’ve got the same Vetterman 4 into 2 system that most RV’s sport, so I see nothing odd there. Anyway, I’d appreciate any inputs anyone might have.
