Rotax fuel regulator

Greg Vos

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Hoping someone can help? We have just replaced the fuel pumps on our xenon, the new pier burg pumps are real expensive and smaller than the 10 year old units we had.
since installing them I have noticed a increase in fuel pressure on the MGL instrument and the return flow to the tank is enthusiastic, now the engine seems to over fuel on start up with very rough running, starting it with pumps off and then once clean idle is established putting on the pumps it’s seems to be ok?
in the past it fired up instantly and settles into a nice 1800 rpm idle, yet with the new pumps I feel it’s over fuelling and this is making the carbs very rich and causing an uneaven idle
so I’m wondering if there is a way to adjust the fuel regulator to reduce the pressure at the carbs and if so how do we go about it ?

looking at our friend google there is not much out there on the fuel regulator and how to adjust it ? We are using the same regulator as in the 914 set up.
any advise or reference to the fuel regulator will be much appreciated
 

Burrengyro

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Hoping someone can help? We have just replaced the fuel pumps on our xenon, the new pier burg pumps are real expensive and smaller than the 10 year old units we had.
since installing them I have noticed a increase in fuel pressure on the MGL instrument and the return flow to the tank is enthusiastic, now the engine seems to over fuel on start up with very rough running, starting it with pumps off and then once clean idle is established putting on the pumps it’s seems to be ok?
in the past it fired up instantly and settles into a nice 1800 rpm idle, yet with the new pumps I feel it’s over fuelling and this is making the carbs very rich and causing an uneaven idle
so I’m wondering if there is a way to adjust the fuel regulator to reduce the pressure at the carbs and if so how do we go about it ?

looking at our friend google there is not much out there on the fuel regulator and how to adjust it ? We are using the same regulator as in the 914 set up.
any advise or reference to the fuel regulator will be much appreciated
Hi Greg,
Have a look at WillyRose's post on Sept 30, 2021: "Training for Emergencies". Fuel pump failure was the problem reported at the time. I am looking forward to hearing more about why this fuel regulator failed in WillyRose's post. Is there something we should be checking as part of our daily inspection?

There is a dome head nut which covers an adjustment screw which regulates the fuel pressure output located at the underside of the regulator. The Rotax heavy maintenance manual is the place to look for info on how to set the pressure. Also, have a look at the following video on Rotax-owner.com's "Fuel pressure checking and adjustment for Rotax 914 engines". The eLearning videos are excellent.
John H.
 

Tyger

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Do have a look at rotax-owner.com forum.
It's a really good forum for all things Rotax related. You do have to subscribe to post there, but anyone can look at what's already been posted.
I assume this is a 914... what pressures are you seeing?
 

Greg Vos

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Do have a look at rotax-owner.com forum.
It's a really good forum for all things Rotax related. You do have to subscribe to post there, but anyone can look at what's already been posted.
I assume this is a 914... what pressures are you seeing?
Hi Tyger we see a varied pressure on the MGL ( I don’t trust it at all) the bar goes full green and in same cases says in the upper corner 10psi, this drops when the engine is running, prior to installing the new fuel pumps we seldom saw any fuel pressure indicated on the MGL but we heard the pumps and the return in the tank before starting.

The xenon maintenance manual says replace pumps after 5 years, so being 10 years despite low hours we decided to do so, thinking it’s a simple old out, new inn maintenance job?
The new pumps are definitely pumping with more flow as the engine is flooding and making startling very difficult and having to open the throttle to full open while cranking to get it to take.
By chance with the assistance of another AP we found that it starts fine if we commence start without any pump on, I have wired our xenon to not put the master on with the master power ( normally the xenon puts the main pump on as your energise the system)
What is confusing me is if the needle and seat is closed now can the addition fuel pressure affect the carbs causing the over fueling? But that’s another matter ?
I really need to understand how to adjust the regulator and am also concerned just turning will or could make it questionable during flight when the pilot demands full power ? So the hunt is on for a person who can explain this regulator operation
 

Greg Vos

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Hi Greg,
Have a look at WillyRose's post on Sept 30, 2021: "Training for Emergencies". Fuel pump failure was the problem reported at the time. I am looking forward to hearing more about why this fuel regulator failed in WillyRose's post. Is there something we should be checking as part of our daily inspection?

There is a dome head nut which covers an adjustment screw which regulates the fuel pressure output located at the underside of the regulator. The Rotax heavy maintenance manual is the place to look for info on how to set the pressure. Also, have a look at the following video on Rotax-owner.com's "Fuel pressure checking and adjustment for Rotax 914 engines". The eLearning videos are excellent.
John H.
Thank you
had a look at chapter 73 in the heavy maintenance manual, says that the regulator is not serviceable and factory set? Does go on to say the set screw can adjust the out put pressure?
they say adjust to xxxx above air box pressure when above xxxx but say adjustment can only be done while engine is off ? So I’m a bit stuck
 

All_In

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Thank you
had a look at chapter 73 in the heavy maintenance manual, says that the regulator is not serviceable and factory set? Does go on to say the set screw can adjust the out put pressure?
they say adjust to xxxx above air box pressure when above xxxx but say adjustment can only be done while engine is off ? So I’m a bit stuck
That's not possible Greg!
The only solution I can think of is trial and error until correct???
I would have to find a way to measure the airbox pressure while running.
Make an adjustment and see what that did until right.
 

Burrengyro

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Thank you
had a look at chapter 73 in the heavy maintenance manual, says that the regulator is not serviceable and factory set? Does go on to say the set screw can adjust the out put pressure?
they say adjust to xxxx above air box pressure when above xxxx but say adjustment can only be done while engine is off ? So I’m a bit stuck
Hi Greg,
Tyger is correct about Rotax-Owner.com. Well worth the few bucks it costs every year and is full of eLearning videos and information on how to do various jobs and gives up-to-date info on the latest SB's and SI's etc., from Rotax. It has a video showing you how to adjust the fuel pressure regulator or if necessary to replace it. It also gives info on faulty regulators and which engine numbers and which regulator numbers may be affected.
John H.
 

Tyger

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What is confusing me is if the needle and seat is closed now can the addition fuel pressure affect the carbs causing the over fueling? But that’s another matter ?
I really need to understand how to adjust the regulator and am also concerned just turning will or could make it questionable during flight when the pilot demands full power ? So the hunt is on for a person who can explain this regulator operation
YES, if there is too much fuel pressure to the carbs it will overcome the up pressure from the floats and flood your float bowl.
The fuel pressure should be approx. 0.25 bar (3.6 p.s.i.) above the pressure at air intake (airbox).
For this reason, the fuel pressure regulator must be connected to the airbox via a pressure connecting line.


I believe the bowl will start to flood if the fuel pressure exceeds the air pressure by about 0.4 bar.
 
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martin-av8r

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The rotax part look like this brand



241%20SCHEMA%20MONTAGGIO.jpg
 

ventana7

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Greg,
I'm curious do you run both pumps at anytime such as for take-off or landing when in the pattern? And if you do run both does this change your fuel pressure?

Rob
 

Greg Vos

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Hi Rob, yes both for take off and landing, the pressure seems to jump on the MGL and we think its unreliable ? So we don’t rely on the pressure gauge

The new pumps do seem to pump more volume and we can hear it returning via the regulator with more vigor than the old OEM Pumps
 

martin-av8r

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Many time it can do this with some type of mechanical fuel pressure regulator

depend on construction and return flow rate vs pump output flow with one or 2 pump on
or if you change fuel pump brand or type and the flow is not the same

or voltage variation with charging system or if you adjust your base fuel pressure with one or 2 pump on , the regulator control the pressure from a restriction - diaphragm ball plunger spring

some yamaha efi with dual fuel pump change base fuel pressure with one or 2 pump on , with the stock fuel pressure regulator on the fuel rail or some aftermarket type when they switch the second pump on some time that up the pressure for the same injector opening time mapped for the lower pressure with only one pump on and this make the engine more fuel ritch an can stumble

anything you change on your fuel system that is not exacly like the old stuff you need to calibrate your base fuel pressure

put a calibrated fluel pressure gauge on your sytem to fine tune your fuel pressure

if your 2 fuel pump on up the pressure more than the rotax spec , and you can lower your pressure with ajusment , normally with one pump on the pressure can drop , fuel pressure regulator difficulty to give the same pressure with one or 2 pump flow difference , and also your fuel pressure regulator is a one to one ratio rising rate with intake pressure vs fuel pressure


some spec info on how new good hardware can take care of problem like this


132628819_226545618873328_5223742260052919484_n.png



So, utilizing a properly set up and configured ECU package , we can guarantee proper compensations which will offer repeatability, reliability, and engine protection functions.
Sometimes these functions are totally transparent, even in data analysis, however in this case, there are a lot of things working here to ensure something as simple as controlling the final fuel mass delivered to the engine is correct.
* Some of the data nerds will enjoy this picture more than others *
Regarding the data plot and “the problems” (we quote that, because many have these 'problems' - they just don’t know they do)
(Bottom Left) This setup has dual fuel pumps because the first pump cannot sufficiently deliver the volume necessary under load. The ECU switches the second pump “on-demand” halfway through the run here, and you can witness the large fuel pressure fluctuations. Fuel pressure fluctuations like this can change the fuel mass delivery massively (it can hardly get any worse than this).
(Bottom Right) The battery voltage is fluctuating almost 2v during the run (bottom left). It seems this may potentially have a voltage regulator issue.
(Top Right) The turbocharger was selected to provide faster spool up, but in some ways, it is too small for heavy load. This can be viewed in the top left where you can see the inlet pressures vs the exhaust pressures. The exhaust pressure skyrockets on the top end over 2:1 (somewhere around 50psi!).
So, with the Emtron Engine Management Electronics, we fully configure the system to overcome the “issues” or “challenges” this engine has.
(Bottom Left) The fuel pressure compensation corrects the fuel mass fairly exactly.
(Bottom Right) The accurate and detailed injector data (3d deadtime and linearization) takes care of the battery voltage issue.
(Bottom Center) The expansion ratio function corrects the “Final VE” for both scenarios where the engine is in positive AND negative pressure ratio (IMAP vs EMAP - see Top Right plot as well). This is a very interesting and somewhat exclusive function of the Emtron fuel/airflow model, and can prove very useful when you have a large pressure ratio fluctuation in the engine like this.
(Top Left) The evidence it all works of course in the one plot we have not mentioned! Observe the lambda target vs actual lambda during the whole run. Please make note, CL trims are 0.0 here. All fuel mass/air flow compensations are happening as a function of feeding forward the system as it should be
 
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martin-av8r

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Also with a setup like this , with the regulator inside creating an ajustable calibrated restriction before the return of the fuel to the tank to create the base fuel pressure we want , to test it , you just squeeze or pinch the return hose that create more restriction and the fuel pressure go up like if you adjust the regulator to a higher pressure

some have problem with return hose to small or restriction and this also up the fuel pressure

these malpassi fuel pressure regulator where use with bike turbo carb kit and weber carb on vw bug and buggy with old turbo blow through carb stuff
 
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