---------------------------------------------------------- RotaxEngines-List Digest Archive --- Total Messages Posted Tue 05/09/06: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:43 AM - engine shudder (Darryl Braun) 2. 07:33 AM - Re: engine shudder (Richard Holder) 3. 09:14 PM - Re: engine shudder (Darryl Braun) ________________________________ Message 1 _____________________________________ Time: 05:43:13 AM PST US From: "Darryl Braun" Subject: RotaxEngines-List: engine shudder --> RotaxEngines-List message posted by: "Darryl Braun" I have a situation I hope someone can shed some light on. I'm running a 912 with a 3 blade Warp Drive prop on a 94 Ultravia Pelican PL. If I pitch the prop for climb and throttle back at altitude I'll get an occasional engine shudder. It actually feels more like someone hit the engine mount with a hammer or something, just a quick thump. The engine never misses a beat. I've tried 2 and 3 blade wood props and finally the Warp Drive to no avail. I've found that keeping a course pitch on the prop kills the proplem completely during cruise, but I'd like to be able to pitch for climb on hot days. When set to a course pitch I can still get the shudder if I decend too fast with out throttling back. So basically if the engine isn't working very hard it tends to have this problem. If I keep it working hard... no problem. I've synced the carbs at every oil change and had the PSRU inspected and nothing changed. I've talked to my mechanic and even to Rotax and they don't know what the deal is. Anyone out there know what's going on? Darryl Braun Ultravia Pelican PL C-GGVS Cold Lake ________________________________ Message 2 _____________________________________ Time: 07:33:34 AM PST US From: Richard Holder Subject: Re: RotaxEngines-List: engine shudder --> RotaxEngines-List message posted by: Richard Holder Darryl Braun wrote: > I have a situation I hope someone can shed some light > on. I'm running a 912 with a 3 blade Warp Drive prop > on a 94 Ultravia Pelican PL. If I pitch the prop for > climb and throttle back at altitude I'll get an > occasional engine shudder. It actually feels more like > someone hit the engine mount with a hammer or > something, just a quick thump. The engine never misses > a beat. I've tried 2 and 3 blade wood props and > finally the Warp Drive to no avail. I've found that > keeping a course pitch on the prop kills the proplem > completely during cruise, but I'd like to be able to > pitch for climb on hot days. When set to a course > pitch I can still get the shudder if I decend too fast > with out throttling back. So basically if the engine > isn't working very hard it tends to have this problem. > If I keep it working hard... no problem. I've synced > the carbs at every oil change and had the PSRU > inspected and nothing changed. I've talked to my > mechanic and even to Rotax and they don't know what the > deal is. Anyone out there know what's going on? I would bet that the engine DOES miss a beat, one or two ! if it happens at the top of the climb when you reduce power for the cruise then it could well be fuel vaporization. How close to the exhaust does your fuel pipe to each carb go ? In the climb there is enough fuel flowing to avoid the problem. then Immediately after reducing power everything is "climb-hot" and and the fuel is flowing slowly -> gets hot -> vaporises -> misfire ! Which stops after 30 seconds or so. I had this and it took me 6 months to find it ! I run my fuel pipes to the carb _over_ the carb now, rather than underneath/ You need a made up union as the banjo won't move to allow an upwards pipe. Even pointing the banjos rearward - away from the exhaust - might help ! A hiccup in the cruise after many minutes is most likely to be carb ice. I assume it is not a continuous problem so it won't be anything to do with the prop ! (Famous last words - sorry !) Richard G-OWWW Europa 912S Airmaster ________________________________ Message 3 _____________________________________ Time: 09:14:39 PM PST US From: "Darryl Braun" Subject: RE: RotaxEngines-List: engine shudder --> RotaxEngines-List message posted by: "Darryl Braun" Thanks Richard Unfortunately it's not carb ice or vapor lock. It will happen from -20 to +30 and my fuel lines are all on top of the engine. It's something related to how hard the engine works. If the engine is turning the prop then it's smooth as silk... if the prop is turning the engine (or the engine is just not working hard) I get a little kick in the pants every few minutes, and it is continuous. I'll keep looking into it and try to record some more data on when it happens. It seems like a harmonic vibration between the engine and the prop, but after 3 different props I know that's not it. I'm wondering if it's ignition. The engine doesn't want to loaf but works well under load. My truck was doing almost the same thing and it turned out to be bad plug wires. If you can think of anything else or hear of anything, please let me know. Thanks again. Darryl Braun Ultravia Pelican PL C-GGVS Cold Lake -----Original Message----- From: owner-rotaxengines-list-server@matronics.com [mailto:owner-rotaxengines-list-server@matronics.com]On Behalf Of Richard Holder Sent: Tuesday, May 09, 2006 7:31 AM Subject: Re: RotaxEngines-List: engine shudder --> RotaxEngines-List message posted by: Richard Holder I would bet that the engine DOES miss a beat, one or two ! if it happens at the top of the climb when you reduce power for the cruise then it could well be fuel vaporization. How close to the exhaust does your fuel pipe to each carb go ? In the climb there is enough fuel flowing to avoid the problem. then Immediately after reducing power everything is "climb-hot" and and the fuel is flowing slowly -> gets hot -> vaporises -> misfire ! Which stops after 30 seconds or so. I had this and it took me 6 months to find it ! I run my fuel pipes to the carb _over_ the carb now, rather than underneath/ You need a made up union as the banjo won't move to allow an upwards pipe. Even pointing the banjos rearward - away from the exhaust - might help ! A hiccup in the cruise after many minutes is most likely to be carb ice. I assume it is not a continuous problem so it won't be anything to do with the prop ! (Famous last words - sorry !) Richard G-OWWW Europa 912S Airmaster