Switch off your fuel supply either in flight at cruise power or on the ground at higher rpm and watch the pressure drop; note when the RPMs start to drop off. The engine runs pretty smooth and at a lower fuel psi than you might imagine.
Where does your drain hose exit or end on the plane or in the cowl? Is it getting any positive pressure from its position?
Do both of you have a fuel re-circulation line and is your fuel hose in fire sleeve?
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
My fuel pump drain line exits at the bottom rear of the cowl, where the airflow thru the cowl exits.
Yes, I have the fuel recirc line installed per Rotax instructions, and my fuel lines are fire-sleeved (except where they split to go to the two carbs).
One thing I have wondered about: My carb vent tubes are routed into the back side of each air filter. Could this be affecting my fuel pressure on full power climbout?
I have almost the identical problem. I replaced an old style pump with the new style and my pressures are very low without the aux electric pump running. (brand new pressure sender)
From a different thread on the 912/914 forum I found out the it is quite possibly caused by my drain line exiting beneath the cowl.
In a nut shell, if there is too much pressure (or too little) in the pump drain line, the diaphragm will not make a full stroke. The pressure and volume will drop. I haven't been able to move my drain line into the cowling yet due to weather but I hope to test it out in a day or two.
No possible way your carb vent tubes can effect fuel pressure. If they did somehow manage to suck enough fuel to lower your pressure, they would be dumping a huge amount of raw fuel into your carbs.
This is really a very common concern with the newer engines/fuel pumps. There are 3 of us here in the Portland, OR area experiencing the same thing and quite a few more I hear on various forums. It would sure be a load off our minds if someone from Rotax would say its OK to set the lower alarm limit at 1.5 psi or so. When the alarm comes on it tends to spook passengers that may be on board even though the engine keeps running fine.
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