Rotax 912ULS Fuel Pressure

[snaproll]

I installed the new fuel pump with overboard drain six months ago in accordance with the Safety Bulletin. Old pump was working well. Went for a short hop this morning and received a panel warning of "high fuel flow", 7.9 GPM on climbout, and noted high fuel pressure, 7 PSI. After I throttled back, all indications returned to normal (3.5 to 4 PSI and 5 GPM at 125 MPH cruise). After landing, I noted fuel stains on the belly. It appears the new fuel pump will dump overboard any time pressure is high. Is anybody else having this same condition? Is this normal? Thanks .. Don (Remos GX)

[roger lee]

Hi Don,

This has been reported with the new fuel pumps. If it over pressures the carb needle valve it flows out the vent tubes into the drip trays. You can also have a couple of drops once in a while go down the drain tube. that does not mean you have a bad pump. If you have an electric fuel pump I personally wouldn't run it all the time. I do not know why the new pump spikes once in a while. I'll be talking to Rotax this week and I'll try and find out if anyone really knows. The fuel gpm went up because the carbs were dumping excess fuel.

[FastEddieB]

Roger,

From what I understand, float height affects the mixture in BINGS*.

So if the bowl is filling to the point of venting overboard, would this not also result in a too-rich mixture?

Source: http://www.leadingedge-airfoils.com/CARBTECH.HTM

[snaproll]

Hi Don,

This has been reported with the new fuel pumps. If it over pressures the carb needle valve it flows out the vent tubes into the drip trays. You can also have a couple of drops once in a while go down the drain tube. that does not mean you have a bad pump. If you have an electric fuel pump I personally wouldn't run it all the time. I do not know why the new pump spikes once in a while. I'll be talking to Rotax this week and I'll try and find out if anyone really knows. The fuel gpm went up because the carbs were dumping excess fuel.

Roger,
Appreciate the info. First time I have noticed this condition. Never happened with the old pump. I seldom turn on the electric pump but normally get 5 PSI with it on and 3.5 to 4 when off. Will monitor it closer and advise of any other occurances. New pump has 6 hour on it, engine time is 87.5 ( just retired and hope to have more time to fly now).
Thanks again.. VR.. Don Stits

[roger lee]

Hi Don,

First question. Do you have a re-circulation line?
Most people seeing high fuel pressure do not have one, have the wrong size orifice in the re-circulation line or they have bad needle valves in the carbs.

[snaproll]

Hi Don,

First question. Do you have a re-circulation line?
Most people seeing high fuel pressure do not have one, have the wrong size orifice in the re-circulation line or they have bad needle valves in the carbs.

Roger,
I do have a re-circulation line back to the tank. Will pull the cowl next weekend and try to determine if the dump overboard is coming from the carb bowl drip trays or the new overboard line installed from the new fuel pump.
VR.. Don Stits

[3Dreaming]

I'm having issues with low pressure and high fuel flow with one of the new pumps.

[snaproll]

I'm having issues with low pressure and high fuel flow with one of the new pumps.

Good luck. Still trying to figure out the high flow rate on mine.. Appears Roger was right as it is dumping into the drip trays. I checked the Remos schematic and the fuel flow sensor is after the distribution block just befor the carbs. Still think the problem is the pump running high pressure - return line is good and flowing. VR.. Don

[roger lee]

You may only need to replace the Viton tipped carb needle valves. I would put a mechanical gauge inline and check the pressure against what you are showing. Float level nees checking too. It could be the pump, but everything else should be ruled out too. Most new pumps run around 4.2 - 5.2

[snaproll]

You may only need to replace the Viton tipped carb needle valves. I would put a mechanical gauge inline and check the pressure against what you are showing. Float level nees checking too. It could be the pump, but everything else should be ruled out too. Most new pumps run around 4.2 - 5.2

Roger,
Problem appears to have cleared. I went to the airport this morning, pulled the cowl, ran the electric fuel pump before startup to check for leaks (none) or fuel dumping into the drip trays (none). Started the Rotax, turned the fuel supply off to allow a burn-off of the fuel in the bowls, turned the fuel back on, and all indications are normal with no leaks. Reinstalled the cowl and flew for 30 minutes – fuel pressure varied from 4.3 to 4.5 PSI, burn rate normal, etc. Will pull the bowls and check for any debris when I do the annual next month but all indications are within operating range and performance is normal.. Go figure... These Swiss Watch engines are different..
VR.. Don Stits

[roger lee]

Hi Don,

IF,
you had a piece of debris in affecting the carb needle valve seat or in the re-circulation line orifice you may have experienced some of these issues.

[snaproll]

Hi Don,

IF,
you had a piece of debris in affecting the carb needle valve seat or in the re-circulation line orifice you may have experienced some of these issues.

Roger,
Finished the annual on my Remos GX. Pulled the bowls and found no debris. All fuel lines are clear and no indication of any prior contamination or particles. The problem has not repeated itself, fuel pressure and burn rate are staying normal. Guess I need to chalk this one up as an anomaly. VR.. Don

[roger lee]

I hate ghost issues, but sometimes they just work out.

[snaproll]

I hate ghost issues, but sometimes they just work out.

Roger,
Thanks for the assistance.. I hate ghost issues also. This is my first Rotax and has taken some time to adapt from the old Continentals, Lycomings, and Franklins of the past. Never minded the geared prop as I have previously flown geared Lycomings (GO-145) and Continentals (GO-300) - the dual carbs is what I have a difficult time with. Aircraft and engine perform well and have been a joy to fly. VR.. Don

[drseti]

- the dual carbs is what I have a difficult time with.

That was the easy part for me, Don. Very common in the British sports car world, as well as with motorcycles. The only difference is, I never before had to deal with a spinning propeller when synchronizing carbs.