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- Aug 17, 2016
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Hi All
I need some advice.
I'm still in the process of working out some issues with my 1939 J3 which I recently imported into Australia from South Africa.
When I received the plane, it had been running on avgas and it engine was running like a dream.
I then acquired an STC from Peterson Aviation to run 95 octane mogas (unleaded but I use a valve lubricant).
One of the guys at my aero club has a 1941 Taylorcraft which also has a Continental Engine A65. His plane has a stromberg carb and my Cub has a Precision Airmotive Carb.
When he switched to Mogas from Avgas, it caused the rubber tipped needle in the carb to swell, this caused fuel starvation, in order to fix this, he had to adjust the float height, or, adjust the little metal tab that the needle rests on in order to increase fuel flow, this fixed his fuel starvation issues.
When I got my Cub, we were expecting the same issues. After about an hour of running mogas, we experienced a power drop (about 150 rpm) in level flight.
I then adjusted the float height to increase the amount of fuel coming into the carb bowl.
We tested the plane again and we found that after about an hour of flying exactly the same thing would happen, the revs would all of a sudden just drop.
I then adjusted the float height to the point where the Cub was getting so much fuel that it was battling to build revs from low rpm, on take off, it would gargle and battle to climb revs, it would puff out clouds of black smoke and once it overcame the low rev range it would then perform properly at a higher rpm.
However, even running the fuel as rich as it is now, the Cub would still experience a power drop after about an hours flying.
I then removed the spark plugs and found that they were all completely fouled. This made me think that my actual problem was perhaps not fuel starvation but rather just fouled plugs, and perhaps I had simply incorrectly diagnosed the issue from the beginning.
I cleaned the plugs with a wire brush and re-installed them without adjusting the carb at all in order to test my theory.
After 3 circuits the plane experienced a major power drop on climb out and we had to turn back an execute a semi powered forced landing, I thought for a moment that we were going to have to set the plane down in the paddock.
I've ordered a new float and viton (metal) needle from Precision Airmotive but I don't know if this is going to fix this issue. I've also order a spark plug tester from Spruce.
Has anyone else experienced something similar or perhaps have any advice?
I've attached pics of the Needle and also the plugs before I cleaned them.
Thanks in advance.
Cheers
Ivan McNamara
I need some advice.
I'm still in the process of working out some issues with my 1939 J3 which I recently imported into Australia from South Africa.
When I received the plane, it had been running on avgas and it engine was running like a dream.
I then acquired an STC from Peterson Aviation to run 95 octane mogas (unleaded but I use a valve lubricant).
One of the guys at my aero club has a 1941 Taylorcraft which also has a Continental Engine A65. His plane has a stromberg carb and my Cub has a Precision Airmotive Carb.
When he switched to Mogas from Avgas, it caused the rubber tipped needle in the carb to swell, this caused fuel starvation, in order to fix this, he had to adjust the float height, or, adjust the little metal tab that the needle rests on in order to increase fuel flow, this fixed his fuel starvation issues.
When I got my Cub, we were expecting the same issues. After about an hour of running mogas, we experienced a power drop (about 150 rpm) in level flight.
I then adjusted the float height to increase the amount of fuel coming into the carb bowl.
We tested the plane again and we found that after about an hour of flying exactly the same thing would happen, the revs would all of a sudden just drop.
I then adjusted the float height to the point where the Cub was getting so much fuel that it was battling to build revs from low rpm, on take off, it would gargle and battle to climb revs, it would puff out clouds of black smoke and once it overcame the low rev range it would then perform properly at a higher rpm.
However, even running the fuel as rich as it is now, the Cub would still experience a power drop after about an hours flying.
I then removed the spark plugs and found that they were all completely fouled. This made me think that my actual problem was perhaps not fuel starvation but rather just fouled plugs, and perhaps I had simply incorrectly diagnosed the issue from the beginning.
I cleaned the plugs with a wire brush and re-installed them without adjusting the carb at all in order to test my theory.
After 3 circuits the plane experienced a major power drop on climb out and we had to turn back an execute a semi powered forced landing, I thought for a moment that we were going to have to set the plane down in the paddock.
I've ordered a new float and viton (metal) needle from Precision Airmotive but I don't know if this is going to fix this issue. I've also order a spark plug tester from Spruce.
Has anyone else experienced something similar or perhaps have any advice?
I've attached pics of the Needle and also the plugs before I cleaned them.
Thanks in advance.
Cheers
Ivan McNamara
