2FlyAgain Posted October 16, 2016 Report Share Posted October 16, 2016 I some times get a high fuel pressure warning on start up. In a recent case , it seemed that it was likely an electrical grounding issue. After retightening the ground bolts, the fuel pressure was better. But, then during run-up one of the ignition circuits dropped about 200 RPM and did not sound good. Normal drop is 110-130 on each side. As I taxied back to the hanger, the engine did not run well at idle RPM. A week later I started the engine again to reproduce the problem. The engine started normally. Again, there was a high fuel pressure indication ranging between 7-10 psi that seemed more stable. During run-up at both 3000 and 4000 RPM both ignition circuits gave similar drops of 120-150 RPM. The fuel pressure settled down to less than 6 PSI. Returning engine all the way to idle and it struggled to run. Note: I have had two mechanics with ROTAX experience try to set the idle down from 2100-2200 RPM with no luck in either case. Now suddenly the engine was idling at 1700 RPM or even less and struggling. I needed to crack the throttle during taxi back to the hangar. The fuel has been Shell 91 octane with no alcohol according to the pump. The carbs were rebuilt during the last five-year rubber change in 2012. After reviewing some threads on this forum, I can think of several possible issues (carb bowl debris, clogged fuel filter, ignition modules, etc.). My question for the forum members is in what order do I suggest that a local mechanic start the trouble shooting process? Thanks in advance… Link to comment Share on other sites More sharing options...
Duane Jefts Posted October 16, 2016 Report Share Posted October 16, 2016 I some times get a high fuel pressure warning on start up. In a recent case , it seemed that it was likely an electrical grounding issue. After retightening the ground bolts, the fuel pressure was better. But, then during run-up one of the ignition circuits dropped about 200 RPM and did not sound good. Normal drop is 110-130 on each side. As I taxied back to the hanger, the engine did not run well at idle RPM. A week later I started the engine again to reproduce the problem. The engine started normally. Again, there was a high fuel pressure indication ranging between 7-10 psi that seemed more stable. During run-up at both 3000 and 4000 RPM both ignition circuits gave similar drops of 120-150 RPM. The fuel pressure settled down to less than 6 PSI. Returning engine all the way to idle and it struggled to run. Note: I have had two mechanics with ROTAX experience try to set the idle down from 2100-2200 RPM with no luck in either case. Now suddenly the engine was idling at 1700 RPM or even less and struggling. I needed to crack the throttle during taxi back to the hangar. The fuel has been Shell 91 octane with no alcohol according to the pump. The carbs were rebuilt during the last five-year rubber change in 2012. After reviewing some threads on this forum, I can think of several possible issues (carb bowl debris, clogged fuel filter, ignition modules, etc.). My question for the forum members is in what order do I suggest that a local mechanic start the trouble shooting process? Thanks in advance… Could it possibly be a choke problem? Is the choke really all the way off after start? Is it lose and variable with engine vibrations? Link to comment Share on other sites More sharing options...
FredG Posted October 17, 2016 Report Share Posted October 17, 2016 I have a 2006 CTsw with experimental registration. Rotax 912 ULS. I had a similar problem with intermittent high idle for no apparent reason. I took the carbs apart, cleaned all the orifices, reassembled the carbs and had no further problems. I have no idea if this is the correct repair for your airplane. As you noted, there are many reasons why a 912 may run poorly. Link to comment Share on other sites More sharing options...
Anticept Posted October 17, 2016 Report Share Posted October 17, 2016 Running on low sleep. Hope this comes out coherent. For it to occur after run up consistently, it makes me think something is aggravated by heat. Unfortunately without looking at it myself, there's still a lot of possibilities. Carbs are still most likely though, especially given the high idle. Also, check plugs. Other ideas: Choke installed wrong Vacuum leak Throttle cable worn Nuts on the throttle arm not secure. Link to comment Share on other sites More sharing options...
Karl Posted October 17, 2016 Report Share Posted October 17, 2016 Also have a look at your carburettor heat ,mine was stuck on due to inner cable folding double just behind the panel . It broke when I tried to straitened it . Link to comment Share on other sites More sharing options...
2FlyAgain Posted October 17, 2016 Author Report Share Posted October 17, 2016 Thanks for the suggestions folks. These will help me get started with the mechanic. Link to comment Share on other sites More sharing options...
cdarza Posted October 18, 2016 Report Share Posted October 18, 2016 You want more ideas ? Check out Aerofix Aviation - they have a very comprehensive Troubleshooting guide. http://www.aerofixaviation.co.uk/rotax912troubleshooting.shtml#VitalEngineStatisticsataglance Link to comment Share on other sites More sharing options...
2FlyAgain Posted October 19, 2016 Author Report Share Posted October 19, 2016 Wow! That is a great troubleshooting guide. A sincere thank you for passing that site along to the forum...!!! Link to comment Share on other sites More sharing options...
2FlyAgain Posted December 22, 2016 Author Report Share Posted December 22, 2016 I found the source of the problem and started a new thread so that people would find it more easily in the future... See the thread titled "Carb Debris (A new source...)" Link to comment Share on other sites More sharing options...
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