Fuel flow issue TSIO 520

[Austintatious]

Hey everyone.  I have been reading and researching a lot.  I even have a call in to Don M about this issue and I dont feel confident I have the answer so far.  Hoping one of you will be able to get me going in the right direction.

Put simply, my FULL power fuel flow is spot on.  However my partial throttle fuel flows are too low. 

I have determined this by making a few observations.

1- When power is left at FULL with 2650 RPM, I can climb at 120 KIAS and CHT's remain below 400

2-  The Fuel flow at FULL POWER matches the charts  (32 GPH)

3-  If power is reduced to 35 inches and 2500 RPM, the fuel flow drops drastically from 32 GPH to 22

         -this is about 5 GPH below the expected fuel flow

         - TIT and CHT rise as soon as power is reduced

Another observation I have made that may have importance is Idle fuel flow.  At 1000 RPM I see a 3.5 GPH fuel flow.  I typically lean to 2.5 gallons which requires quite a few turns on the mixture know.  Also, the aircraft starts much more readily if the mixture knob is already pulled out about .5 inches for the start.

OBVIOUSLY if the engine runs cool at FULL power, it should be even cooler at a lower power setting, but I see the opposite due to the leaner and hotter mixture at partial power.    

I have found verbiage in the Continental maintenance manual that states that the maximum part throttle FULL RICH fuel flow will be achieved with the Idle un-metered fuel pressure set for the lowest value.  The thing is, as far as I can tell, my Idle mixture rise seems to be spot on at about 50 RPM.  

I do not fully understand the procedure in the manual for setting all the fuel parameters.  As far as I can tell however, there is only 4 things that can be adjusted

1- Idle stop screw  ( Not really relevant, however I believe I need to adjust this as I can pull the throttle out to 700 rpm, Minimum should be 1000)

2- idle mixture  adjustment screw

3- Full throttle un-metered fuel pressure  (aneroid adjustment)

4- un-metered fuel pressure  (low pressure relief valve)

 

So thinking out loud....

The manual does not state any interrelation to these various adjustments, however I have to believe they will be interrelated and thus affect each other.

Obviously my main problem is the low fuel flow at partial throttle settings.  To remedy that it appears I need to lower my Idle un-metered fuel pressure with the low pressure relief valve.

I suspect that action will affect my idle mixture ( which I believe is to high right now) and may possibly make it too lean at idle.  I would then need to adjust my Idle mixture adjustment screw to compensate for this.  

 

Do I have this right?  I cant find any mechanics that seem to know about this or are otherwise able to tell me what is going on.   Sorry if this was a difficult read.  I really appreciate any help.

[aviatoreb]

1 hour ago, Austintatious said:

Hey everyone.  I have been reading and researching a lot.  I even have a call in to Don M about this issue and I dont feel confident I have the answer so far.  Hoping one of you will be able to get me going in the right direction.

Put simply, my FULL power fuel flow is spot on.  However my partial throttle fuel flows are too low. 

I have determined this by making a few observations.

1- When power is left at FULL with 2650 RPM, I can climb at 120 KIAS and CHT's remain below 400

2-  The Fuel flow at FULL POWER matches the charts  (32 GPH)

3-  If power is reduced to 35 inches and 2500 RPM, the fuel flow drops drastically from 32 GPH to 22

         -this is about 5 GPH below the expected fuel flow

         - TIT and CHT rise as soon as power is reduced

Another observation I have made that may have importance is Idle fuel flow.  At 1000 RPM I see a 3.5 GPH fuel flow.  I typically lean to 2.5 gallons which requires quite a few turns on the mixture know.  Also, the aircraft starts much more readily if the mixture knob is already pulled out about .5 inches for the start.

OBVIOUSLY if the engine runs cool at FULL power, it should be even cooler at a lower power setting, but I see the opposite due to the leaner and hotter mixture at partial power.    

I have found verbiage in the Continental maintenance manual that states that the maximum part throttle FULL RICH fuel flow will be achieved with the Idle un-metered fuel pressure set for the lowest value.  The thing is, as far as I can tell, my Idle mixture rise seems to be spot on at about 50 RPM.  

I do not fully understand the procedure in the manual for setting all the fuel parameters.  As far as I can tell however, there is only 4 things that can be adjusted

1- Idle stop screw  ( Not really relevant, however I believe I need to adjust this as I can pull the throttle out to 700 rpm, Minimum should be 1000)

2- idle mixture  adjustment screw

3- Full throttle un-metered fuel pressure  (aneroid adjustment)

4- un-metered fuel pressure  (low pressure relief valve)

 

So thinking out loud....

The manual does not state any interrelation to these various adjustments, however I have to believe they will be interrelated and thus affect each other.

Obviously my main problem is the low fuel flow at partial throttle settings.  To remedy that it appears I need to lower my Idle un-metered fuel pressure with the low pressure relief valve.

I suspect that action will affect my idle mixture ( which I believe is to high right now) and may possibly make it too lean at idle.  I would then need to adjust my Idle mixture adjustment screw to compensate for this.  

 

Do I have this right?  I cant find any mechanics that seem to know about this or are otherwise able to tell me what is going on.   Sorry if this was a difficult read.  I really appreciate any help.

Something is wrong - my TSIO520NB is also as book at full power 2650-38'' but pulled back to 2500-35'' fuel flow goes to 27-27.5 gph.

[Austintatious]

Update:

Adjusted the Idle un-metered fuel pressure down today and the part throttle fuel flows went up, however so did the Full power fuel flow.  This had been adjusted a few days ago by 1/2 turn to increase fuel flow.  I was getting 38-40 GPH at full power so I went back a quarter turn.  Didn't have time to fly it again so I will probably go out tomorrow and do a few things and test fly it.

I am speculating as to what happened, but I suspect the Idle un-metered fuel pressure adjustment moved.  The jam nut was not very tightly secured and this may have allowed the adjustment to wonder, which effected both full power and part throttle fuel flows.

Everything should be pretty close to spot on now.

Edited November 14, 2019 by Austintatious

[aoaviation]

On 11/12/2019 at 2:13 PM, Austintatious said:

Hey everyone.  I have been reading and researching a lot.  I even have a call in to Don M about this issue and I dont feel confident I have the answer so far.  Hoping one of you will be able to get me going in the right direction.

Put simply, my FULL power fuel flow is spot on.  However my partial throttle fuel flows are too low. 

I have determined this by making a few observations.

1- When power is left at FULL with 2650 RPM, I can climb at 120 KIAS and CHT's remain below 400

2-  The Fuel flow at FULL POWER matches the charts  (32 GPH)

3-  If power is reduced to 35 inches and 2500 RPM, the fuel flow drops drastically from 32 GPH to 22

         -this is about 5 GPH below the expected fuel flow

         - TIT and CHT rise as soon as power is reduced

Another observation I have made that may have importance is Idle fuel flow.  At 1000 RPM I see a 3.5 GPH fuel flow.  I typically lean to 2.5 gallons which requires quite a few turns on the mixture know.  Also, the aircraft starts much more readily if the mixture knob is already pulled out about .5 inches for the start.

OBVIOUSLY if the engine runs cool at FULL power, it should be even cooler at a lower power setting, but I see the opposite due to the leaner and hotter mixture at partial power.    

I have found verbiage in the Continental maintenance manual that states that the maximum part throttle FULL RICH fuel flow will be achieved with the Idle un-metered fuel pressure set for the lowest value.  The thing is, as far as I can tell, my Idle mixture rise seems to be spot on at about 50 RPM.  

I do not fully understand the procedure in the manual for setting all the fuel parameters.  As far as I can tell however, there is only 4 things that can be adjusted

1- Idle stop screw  ( Not really relevant, however I believe I need to adjust this as I can pull the throttle out to 700 rpm, Minimum should be 1000)

2- idle mixture  adjustment screw

3- Full throttle un-metered fuel pressure  (aneroid adjustment)

4- un-metered fuel pressure  (low pressure relief valve)

 

So thinking out loud....

The manual does not state any interrelation to these various adjustments, however I have to believe they will be interrelated and thus affect each other.

Obviously my main problem is the low fuel flow at partial throttle settings.  To remedy that it appears I need to lower my Idle un-metered fuel pressure with the low pressure relief valve.

I suspect that action will affect my idle mixture ( which I believe is to high right now) and may possibly make it too lean at idle.  I would then need to adjust my Idle mixture adjustment screw to compensate for this.  

 

Do I have this right?  I cant find any mechanics that seem to know about this or are otherwise able to tell me what is going on.   Sorry if this was a difficult read.  I really appreciate any help.

Hi, we are having the exact same problem and have made all the adjustments you made. Did you ever solve the issue? 

[aviatoreb]

1 hour ago, aoaviation said:

Hi, we are having the exact same problem and have made all the adjustments you made. Did you ever solve the issue? 

I have mine set to 33 in full power 38'' 2650 (but it often seems like it will be like 37.7 or .8 and 2650 to 2670), and cruise climb 35-2500 comes out at 27-27.2 gph. Cooling seems good.

[carusoam]

Welcome aboard, AOAviation!

Austin has been away for a couple of weeks... not too long...

Depending on how he set up his account... he may have received an email when you ask your question...

Best regards,

-a-

[67 m20F chump]

Read continental sid97-3g.  Find a good mechanic that has the equipment to do the work.  Sounds like your idle mixture is off at a minimum.  The sid says how much rpm rise you should get at 600 rpm I think when you go to cut off.   I had to go through this with my Beechcraft.  

[Austintatious]

On 11/21/2020 at 8:00 PM, aoaviation said:

Hi, we are having the exact same problem and have made all the adjustments you made. Did you ever solve the issue? 

No, cant seem to find a mechanic with the knowledge or tools.

[Guest]

2 hours ago, Austintatious said:

No, cant seem to find a mechanic with the knowledge or tools.

I loaded a procedure that I found in the Safety and Techniques section.  It’s a fairly straightforward process.  You need a very accurate 0-15 PSI gauge with a positive shut off valve, a 1/4” swivel T fitting and a 1/4” hose about 8’ long. Some basic hand tools, wrenches etc.

Happy to walk you through it remotely.

 

Clarence

[Austintatious]

8 hours ago, M20Doc said:

I loaded a procedure that I found in the Safety and Techniques section.  It’s a fairly straightforward process.  You need a very accurate 0-15 PSI gauge with a positive shut off valve, a 1/4” swivel T fitting and a 1/4” hose about 8’ long. Some basic hand tools, wrenches etc.

Happy to walk you through it remotely.

 

Clarence

I am familiar with the procedure and the things one can do wrong to cause this issue, I just do not have the tools.

When setting the metered and UN-metered pressure, the manual states that the fuel pressure regulator must be taken out of the system, then the values set 5% higher than book specifications.  The fuel pressure regulator is then reconnected and adjusted to get the proper full throttle fuel flow.  The manual states that this is critical or the partial throttle fuel flow will not be adequate. 

I believe whoever set this failed to do this and that is why I am having issues.  I need more than just the fittings you mentioned, I also need the stuff to remove and cap the fuel pressure regulator.

[Guest]

3 hours ago, Austintatious said:

I am familiar with the procedure and the things one can do wrong to cause this issue, I just do not have the tools.

When setting the metered and UN-metered pressure, the manual states that the fuel pressure regulator must be taken out of the system, then the values set 5% higher than book specifications.  The fuel pressure regulator is then reconnected and adjusted to get the proper full throttle fuel flow.  The manual states that this is critical or the partial throttle fuel flow will not be adequate. 

I believe whoever set this failed to do this and that is why I am having issues.  I need more than just the fittings you mentioned, I also need the stuff to remove and cap the fuel pressure regulator.

I’ve never worked on a rocket, but what you’re describing is a typical 340/414 fuel system.  If it’s the same regulator, to disable it, you need an AN 806-4D plug for the line and an AN 929-4D.  You cap the centre port of the regulator to make your adjustments on the pump them reconnect it for final adjustments for take off power.  

The regulator requires a 3/8” wrench to loosen the check nut and a 3/32” Allen wrench to turn the adjustment screw.

The low unmetered pump adjustment requires a 3/8” wrench for the check nut and a 5/16” to turn the adjustment screw.

The aneroid requires a 3/8” wrench for the check nut and a fine blade common screwdriver to turn the adjustment screw.

Clarence