Art_N412SB
Member
Those of us with E-LSA RV-12's sometimes do our maintenance "on condition". I would like to share with you some of the symptoms that we experienced that lead us to believe it was time get our carburetors overhauled.
The following is a lessons learned email that I sent to my co-owners.
Hopefully there may be something in here that may be a benefit to you.
Dear friends,
Jeff and I flew our aircraft yesterday post carburetor rebuild. Lockwood Aviation did the overhaul for just under $600 for both carburetors. I have to tell you that the difference is night and day.
Prior to the overhaul we were noticing some symptoms. For the last year we had some vibration between 2800 and 3800 RPM. Most noticeable when descending and slowing down. Starting was becoming an issue as well.
When I first started flying our aircraft starting cold with full choke was good. Soon after start the choke would no longer be needed. I feel the choke is not the right name for the control. The air is not choked off or restricted in any way. Rather the fuel air mixture is enriched for starting cold. I would call it a fuel enrichment control.
In the last year or so I noticed that the choke started to have a sweet spot. In other words pulling the choke control full out the engine would bang around and fire up really rough. I started using half choke for starting. Then latter yet I would using one quarter choke. Full choke was actually flooding the engine.
Another symptom was that the first mag check would be 320 RPM drop, but the second mag check would be OK at 100 to 120 mag drop. The bad drop was mostly on system A. I think the plugs were getting carboned up during taxi and needed to be burned off before we got a good mag check. By the way the RV-12 POH refers to this check as a “Mag” check. So I don’t feel bad about calling it a mag check. I know it is a ignition system check.
Then as things got really bad the engine was hesitating while advancing above 2500 RPM through 3800 rpm and being quite rough. This was when we decided to get the carbs overhauled.
When I talked with Joe at Lockwood Aviation, he said it was the idle jet getting gummed up. Also we had some heavy floats. Keith and I had weighed the floats prior to shipping them out, but we did that with my wife’s kitchen scales. The scales were not really calibrated. So we got to get better scales before next time. But, even if they were not overweight we would still have to change them out for new ones anyway. You see they were Bing manufactured floats and we needed the newer Rotax manufactured floats. You can check this by the Rotax floats havening an “R” stamped on the floats. The Bing Carburetors have a “B”.
So all that combined, we were actually flooding the engine. Prior to sending out the carbs we pulled the spark plugs and found that all 4 plugs on the front two cylinders were very black. The four plugs on the two aft cylinders were clean. Joe at Lockwood explained that since the carburetors are located on the back end of the engine the shape and distance of the intake manifold actually causes a different fuel air ratio to the front two cylinders. I suppose that when the idle jet gets gummed up and the floats get heavy the mixture becomes richer for all cylinders but very rich for the front two cylinders.
All of these symptoms have disappeared. The engine is running great. I have less than 150 hours flying the Rotax 912. It has a different feel from the Continental and Lycoming engines that I have flown in the past. Those engines have a smother feel at Idle RPM. The Rotax feels like it bangs around a little more than the other engines. I think this is due to the smaller higher compression cylinders. Not bad, just different.
I hope you found something of use here.
The following is a lessons learned email that I sent to my co-owners.
Hopefully there may be something in here that may be a benefit to you.
Dear friends,
Jeff and I flew our aircraft yesterday post carburetor rebuild. Lockwood Aviation did the overhaul for just under $600 for both carburetors. I have to tell you that the difference is night and day.
Prior to the overhaul we were noticing some symptoms. For the last year we had some vibration between 2800 and 3800 RPM. Most noticeable when descending and slowing down. Starting was becoming an issue as well.
When I first started flying our aircraft starting cold with full choke was good. Soon after start the choke would no longer be needed. I feel the choke is not the right name for the control. The air is not choked off or restricted in any way. Rather the fuel air mixture is enriched for starting cold. I would call it a fuel enrichment control.
In the last year or so I noticed that the choke started to have a sweet spot. In other words pulling the choke control full out the engine would bang around and fire up really rough. I started using half choke for starting. Then latter yet I would using one quarter choke. Full choke was actually flooding the engine.
Another symptom was that the first mag check would be 320 RPM drop, but the second mag check would be OK at 100 to 120 mag drop. The bad drop was mostly on system A. I think the plugs were getting carboned up during taxi and needed to be burned off before we got a good mag check. By the way the RV-12 POH refers to this check as a “Mag” check. So I don’t feel bad about calling it a mag check. I know it is a ignition system check.
Then as things got really bad the engine was hesitating while advancing above 2500 RPM through 3800 rpm and being quite rough. This was when we decided to get the carbs overhauled.
When I talked with Joe at Lockwood Aviation, he said it was the idle jet getting gummed up. Also we had some heavy floats. Keith and I had weighed the floats prior to shipping them out, but we did that with my wife’s kitchen scales. The scales were not really calibrated. So we got to get better scales before next time. But, even if they were not overweight we would still have to change them out for new ones anyway. You see they were Bing manufactured floats and we needed the newer Rotax manufactured floats. You can check this by the Rotax floats havening an “R” stamped on the floats. The Bing Carburetors have a “B”.
So all that combined, we were actually flooding the engine. Prior to sending out the carbs we pulled the spark plugs and found that all 4 plugs on the front two cylinders were very black. The four plugs on the two aft cylinders were clean. Joe at Lockwood explained that since the carburetors are located on the back end of the engine the shape and distance of the intake manifold actually causes a different fuel air ratio to the front two cylinders. I suppose that when the idle jet gets gummed up and the floats get heavy the mixture becomes richer for all cylinders but very rich for the front two cylinders.
All of these symptoms have disappeared. The engine is running great. I have less than 150 hours flying the Rotax 912. It has a different feel from the Continental and Lycoming engines that I have flown in the past. Those engines have a smother feel at Idle RPM. The Rotax feels like it bangs around a little more than the other engines. I think this is due to the smaller higher compression cylinders. Not bad, just different.
I hope you found something of use here.