Throttle springs
I did not like the strong throttle springs pulling the throttle control out of my hand or causing the throttle to slowly advance. So I replaced the original springs with Century Spring part number 6049. I could not find any stock spring with the properties that I wanted, but the 6049 came closest. The 6049 is 2" long and needs to be shortened 1/4" to work on the Rotax carburetors. The original springs are made with approximately 0.045" plated steel and both ends are clocked the same. The Century 6049 springs measured about 0.040" and are made of music wire and the ends are clocked 90? apart. After cutting and bending the extended hook on one end, I baked the springs at 400? in the kitchen oven for an hour to relieve stresses. I do not know if that was necessary or not, but it did not hurt the springs. At idle, the original springs pull with 8 pounds of force compared to Century Spring 6049 at 4 pounds. Although the throttle will still creep forward if the friction knob is not tightened enough, the weaker 6049 springs have improved throttle operation. I have flown one test flight with the new springs, and made several touch and goes without a problem.
Century Spring has a minimum order, so I have extra springs.
Rotax does not approve the 912ULS for IFR. Now that I have modified the engine with new springs, it is no longer a Rotax engine but a Joe's Special approved for IFR. At least that is my story and I am sticking to it.
Joe
I did not like the strong throttle springs pulling the throttle control out of my hand or causing the throttle to slowly advance. So I replaced the original springs with Century Spring part number 6049. I could not find any stock spring with the properties that I wanted, but the 6049 came closest. The 6049 is 2" long and needs to be shortened 1/4" to work on the Rotax carburetors. The original springs are made with approximately 0.045" plated steel and both ends are clocked the same. The Century 6049 springs measured about 0.040" and are made of music wire and the ends are clocked 90? apart. After cutting and bending the extended hook on one end, I baked the springs at 400? in the kitchen oven for an hour to relieve stresses. I do not know if that was necessary or not, but it did not hurt the springs. At idle, the original springs pull with 8 pounds of force compared to Century Spring 6049 at 4 pounds. Although the throttle will still creep forward if the friction knob is not tightened enough, the weaker 6049 springs have improved throttle operation. I have flown one test flight with the new springs, and made several touch and goes without a problem.
Century Spring has a minimum order, so I have extra springs.
Rotax does not approve the 912ULS for IFR. Now that I have modified the engine with new springs, it is no longer a Rotax engine but a Joe's Special approved for IFR. At least that is my story and I am sticking to it.
Joe