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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R44/22 H269/300 MD 500 Magni (all); Xenon RST; DTA; ELA; MTO Trojan
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Stoped counting at 2000
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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R44/22 H269/300 MD 500 Magni (all); Xenon RST; DTA; ELA; MTO Trojan
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Stoped counting at 2000
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.
 
Last edited:

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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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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