Rotax 914/912 Carb Sync the Cheapskate Method - Part 1 Mechanical Sync

Sync the Carbs on Rotax 914/912

[@cardocarnut4665]

Thanks for the detailed instructions on the mechanical sync - I learned quite a lot. :) After performing the pneumatic sync with gauges, I now get 3.25 gallons per hour at near 5,000RPM. I did verify my gauges against each other - no need to calibrate them you just want relative readings to each other to match or the difference noted. After much testing I found closing the balance tube with clamps just did not work even with two clamps. I had to completely disconnect the balance tube and cap the now open ends. I prefer using gauges rather than the CarbMate electronic sync box as I can see actually what actually is happening - not assuming. BTW once the balance tube is reconnected the gauges showed the carbs were not in sync or not as well as before reconnecting but that is the procedure Rotax provides, and I believe it is correct due to my smooth-running engine and great fuel mileage.

[@goldenoldie3524]

Thank you for the detailed comment. I haven't done the pneumatic sync yet. Too lazy. I've got the gauges all setup and have valves installed to stabilize the needles. My engine is very smooth with just the mechanical sync (one of the reasons I've haven't done the other sync). I'm burning five gallons an hour at 5,000 RPM. Do you have a 912 or 914? Rick

[@thomasmorgera4858]

Rick, Great video. Additional question for you: not clear as to when to attach the cable to the arm…. How do you tighten the 8mm nut with the throttle closed?

[@goldenoldie3524]

Thanks. Attach the cables to the arms as the last step. Fully open the throttle lever. Attach the spring in the operating position. Attach the cables so that they both start to pull back on the arm at the same time when the control lever is pulled back. Use a gap gauge to measure the distance between the arm and the fully opened stops to make sure they are the same. Rick

[@timtaylor9339]

Wanted to double check. 0.004- or 0.04-inches gap on the idle set point.? 1 1/2 turns seem like much more than 0.004 inches.

[@goldenoldie3524]

Hi Tim. Page 144 of the line service manual "Insert a 0.1 mm (0.004 in.) feeler gauge (gap X) between the idle speed adjust-ment screw (2) and the carburetor idle stop (3), then gently turn the idle screw clockwise until contact is made with the 0.1 mm (0.004 in.) feeler gauge." The point is to get both idle positions the same. You'll re-adjust the idle screw to set the correct idle speed after the process by turning both screws the same amount to get the best idle speed. Rick

[@timtaylor9339]

@@goldenoldie3524 Rick, thanks for the explanation. I had listened several times but still missed the need to open the throttle slightly after setting the 0.004 gap. I was envisioning the set screw hitting the stop when it was turned in 1-1/2 turns. I just had my carbs rebuilt and this is my first time trying to set them up from scratch. I was able to complete the process today. Thanks, hopeful they will be close when I test run the engine later this week.

[@timtaylor9339]

Part 2?

[@goldenoldie3524]

One of these days. Mechanical worked so well I'm not in a real hurry even though I've got the gauges built and ready to go. And I'm lazy. Thanks. Rick

[@timtaylor9339]

@@goldenoldie3524 Thanks, I was just hoping to see the comparison of the two methods. I am not a fan of standing next to a moving propeller to balance the carbs.

[@goldenoldie3524]

@@timtaylor9339 That's the other reason I'm in no hurry. Rick

[@dh-flies]

Hey Rick, did the EarthX battery fit in the stock battery box? And if so what is their part number? I want to put a lithium in my plane. I am assuming the Rotax alternator will charge it...right? lol

[@goldenoldie3524]

Rich installed the battery before I took delivery. I'll get the battery number the next time I have the top cowl off. Stator has no problem charging. Rick