tevbax Posted July 26, 2022 Report Share Posted July 26, 2022 Finally got all the BRS mess wrapped up and went for a test flight last night. Full power on departure, other than trim being way out of whack, it flew great! So, grabbed a friend and went back up for a longer flight. He's getting used to the plane, so did a series of steep turns, flew past our homes, and headed back to the airport. Engine was running at approx 4800 RPM. Then, the surging started. Engine RPM would drop to 3200 then back to 4500 back to 3200 back to 4800 - like a timed oscillation. The engine did run fine at idle for the landing with no sign of issues. This plane has had the carbs rebuilt, linked and synced. Annual was just done in March. Previous owner ran only 91 non-ethanol fuel. All AD's and SB's have been completed. Vents are all facing forward, and fuel is water free/ contaminant free through the gascolator. Any ideas on where to start looking? My first thought is something floating around in the float bowls. Since the main was active during the surge, and it idled fine, that kind of tells me that something was plugging the main. Run up after on the ground revealed no surging or hesitation. Video link below - watch the tach. CTSW - 2006 Rotax 912 ULS Video P.S. Don't judge the landing Quote Link to comment Share on other sites More sharing options...
Anticept Posted July 26, 2022 Report Share Posted July 26, 2022 Take em off and clean em. I had a flake of debris that would only become an issue at high power settings. It would then clog a nozzle, if you pulled powere back, the flake would fall back to the bottom of the bowl again and smooth out. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted July 26, 2022 Report Share Posted July 26, 2022 I agree with Corey. Just because something was cleaned a while ago doesn’t mean it can’t be the issue now. I would open the fuel filter behind the dash, open the gascolator and remove and clean the carbs. My money says these things will help you. Quote Link to comment Share on other sites More sharing options...
cdarza Posted July 27, 2022 Report Share Posted July 27, 2022 i agree X3 My carb bowl was cleaned the day before. I went out for a flight and engine grumbled as i was passing 800ft on the takeoff. Found a couple small black flakes from the float in the bowl. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted July 27, 2022 Report Share Posted July 27, 2022 Not just the float bowl. The entire carb. Quote Link to comment Share on other sites More sharing options...
tevbax Posted July 29, 2022 Author Report Share Posted July 29, 2022 So, here's an interesting turn. I talked with Brett @ Leading Edge at Airventure. When our mechanic put our carbs back together from Leading edge, he neglected to hook up the carb balance tube that runs through the airbox. The tubes that are on the carbs were exactly where Leading edge left them - in the hangers that hold the float bowls on. Heading to the airport tonight to reattach the balance tube. Carb bowls were absolutely spotless with NO sign of residue or debris. Quote Link to comment Share on other sites More sharing options...
Anticept Posted July 30, 2022 Report Share Posted July 30, 2022 That will absolutely cause funky issues. Depending on airspeed and AoA, there can be fluctuations in pressure under the cowl which will affect the fuel flow through the jets. Good catch. Fortunately that wouldn't necessarily result in harm, you likely wouldn't have lost power completely, but certainly scary. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted July 30, 2022 Report Share Posted July 30, 2022 Unfortunately when using text, emails or anything in print you get a story, but maybe not all small details and you just have to assume something’s are in place or have already been done. This is why I usually prefer phone calls. It’s usually quicker and far more informative. Quote Link to comment Share on other sites More sharing options...
tevbax Posted July 30, 2022 Author Report Share Posted July 30, 2022 1 hour ago, Roger Lee said: Unfortunately when using text, emails or anything in print you get a story, but maybe not all small details and you just have to assume something’s are in place or have already been done. This is why I usually prefer phone calls. It’s usually quicker and far more informative. This for me was a detail I knew nothing about. When i asked the A&P what the little plastic tube coming out of the airbox was for, he stated that it held in the air filter. I've had a good laugh this week. Flew the plane last night, no sign of surging. But, only beat the pattern. Ill get a longer flight tomorrow after im done working at Airventure. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted July 30, 2022 Report Share Posted July 30, 2022 Go to school on the Rotax 912, you will be more informed than most A&P's. It will be the best money you ever spent on your plane. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted July 30, 2022 Report Share Posted July 30, 2022 if things work out like I hope I'll have a class Oct. 15-16 Quote Link to comment Share on other sites More sharing options...
tevbax Posted July 31, 2022 Author Report Share Posted July 31, 2022 On 7/30/2022 at 10:09 AM, Madhatter said: Go to school on the Rotax 912, you will be more informed than most A&P's. It will be the best money you ever spent on your plane. Doing the Rainbow class in November. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted July 31, 2022 Report Share Posted July 31, 2022 yes they are. I might change them if anyone from the fly-in wants to come. I need to look at my schedule. I'm usually very busy in Oct. Quote Link to comment Share on other sites More sharing options...
Anticept Posted March 17, 2023 Report Share Posted March 17, 2023 On CTSWs, yes there is a tube that you should have holes in it in the airbox. Float bowl pressure is quite important. Quote Link to comment Share on other sites More sharing options...
procharger Posted March 17, 2023 Report Share Posted March 17, 2023 Float level check?? Who set the 10.5 ? Quote Link to comment Share on other sites More sharing options...
Anticept Posted March 17, 2023 Report Share Posted March 17, 2023 Put some avgas in and see if the issue goes away. If it does, it's vapor issues. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted March 17, 2023 Report Share Posted March 17, 2023 1 hour ago, Danilo209 said: Does the teflon tube that connects through the airbox is supposed to have a slit through it to let clean air in? I'm having stumbling issues with WOT on take off and this is something I'm not sure if its factory or something the PO did. The idea is that the vent tube should have the same pressure as the inlet of the filtered air to the carb. Make sure all of the slits in the tube are inside the airbox. If one gets outside it will cause issues. Quote Link to comment Share on other sites More sharing options...
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