---------------------------------------------------------- RotaxEngines-List Digest Archive --- Total Messages Posted Mon 07/02/07: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:07 AM - Re: 914 fuel pressure () ________________________________ Message 1 _____________________________________ Time: 09:07:13 AM PST US Subject: Re: RotaxEngines-List: 914 fuel pressure From: Hello Lynn "Can anyone please tell me what the fuel pressure should be on a 914; with and with out the second (auxiliary) pump." Very close to between 2 and 5 PSI above airbox pressure. Look up exacts in Rotax Manual. This is absolute pressure so it is same at sea level and 18K, same 1 or 2 pumps, it is output of fuel pressure regulator to carb float bowls. The pressure between ambient and what the fuel pump/s output is moot on a 914. The fuel pump labor will change, the higher you go the harder they have to work to maintain flow and pressure to insure the fuel pressure regulator can maintain 2 to 5 PSI. Who cares what pressure the output side of the pump/s is, just it is capable of netting 2 to 5PSI to carb float bowls. You need to watch out using parallel fuel pumps you don't blow above the 5 psi. I chose series with bypass. Remember that the fuel pressure regulator constant returns fuel to tanks, you need to make sure there is not much restriction from FPR to tank, read exact check in manual, parallel worst as far as blowing over 5PSI. You not only need good fuel pressure from pumps, but good flow as well to supply motor. The Fuel Pressure Regulator I believe is sized with not much excess pressure ability above what is needed at 115%. From what I understand if wastegate sticks closed and you over boost, you will fall below 2 PSI and hence run out of fuel, boost drops, carbs fill, engine catches, etc. etc. etc. This is one form of "Surging" that can occur. Also if filter or gasculator is clogged, or filter in pump intake is clogged or if a pump is malfunctioning. IMHO all planes with 914 should have a differential pressure gauge installed. One supplier is UMA. If for any reason you see needle fall below 2 PSI, you are in danger of running out of fuel. Turning on second pump, going lower in altitude and or switching to a second filter can help as well as trying a lower power setting. Of course the most critical part of flight, right after take off is the time you most don't want a power out. For any of the above mentioned reasons, when you dial up full power, and the differential gauge shows less than 2 PSI, there is a good chance the motor can quit in 20 seconds. It will run perfect till that time. Smart move to glance at differential needle when rolling, and abort if low. If you get the surging I mentioned, if you see that the needle is falling below 2 PSI and you reduce power and the needle goes above, there is a very good chance that the motor will continue to run. You may find some useful info here: http://contrails.free.fr/engine_914_fuel_syst_test_en.php Ron Parigoris ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message rotaxengines-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/RotaxEngines-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/rotaxengines-list Browse Digests http://www.matronics.com/digest/rotaxengines-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.