Freshly overhauled IO-360-A3B6 - max fuel flow too high?

[Ryan ORL]

Hey all,

tl;dr - New engine is running richer than the old one and I believe it is causing the mag checks to be rough

I just had my IO-360-A3B6 major overhauled by an engine shop down in South Florida.  They ran it 3 hours in the test cell and it's back on the airplane now and I've done a couple break-in flights, and fortunately things are mostly looking good so far, and my install shop has helped me fix a few gremlins w/ the (also freshly overhauled) governor, etc.

However, one remaining issue is that my mag checks are considerably rougher than I would expect, dropping in some cases almost 200rpm.  The mags seem timed close to each other, the split isn't much.  Yesterday I decided to debug this issue a bit, and I noted that there is the proper rise of EGT on all 4 cylinders on both mags, so I don't think there is any issue with bad plugs.

I had noticed that on my first takeoff (when I was watching all the indications quite closely) that my takeoff fuel flow was higher than normal, hitting around 20.5 gal/hr.  My old engine hit around 18.5 gal/hr on takeoff.  (From my research on the forum here, that seems to be the correct value, approximately)  Takeoff power felt normal, and probably a bit stronger than the old engine, and I suspect my old engine was down a bit on performance, so a bit higher fuel flow isn't terribly surprising, but I didn't expect that much more flow.

Anyway, based on this, I suspected that my full-rich mixture setting is a too rich.  So I repeated the mag check with the mixture slightly pulled back, and the mag checks were totally normal.  I also noted the full-rich runup RPM (2000) fuel flows were also higher than the old engine.  I suspect the fuel flows are higher across the board.

Based on my reading, this is basically not adjustable... so I think it's potentially an issue with the fuel servo and I guess I need to contact the engine shop for their opinion?

[LANCECASPER]

27 minutes ago, Ryan ORL said:

Hey all,

tl;dr - New engine is running richer than the old one and I believe it is causing the mag checks to be rough

I just had my IO-360-A3B6 major overhauled by an engine shop down in South Florida.  They ran it 3 hours in the test cell and it's back on the airplane now and I've done a couple break-in flights, and fortunately things are mostly looking good so far, and my install shop has helped me fix a few gremlins w/ the (also freshly overhauled) governor, etc.

However, one remaining issue is that my mag checks are considerably rougher than I would expect, dropping in some cases almost 200rpm.  The mags seem timed close to each other, the split isn't much.  Yesterday I decided to debug this issue a bit, and I noted that there is the proper rise of EGT on all 4 cylinders on both mags, so I don't think there is any issue with bad plugs.

I had noticed that on my first takeoff (when I was watching all the indications quite closely) that my takeoff fuel flow was higher than normal, hitting around 20.5 gal/hr.  My old engine hit around 18.5 gal/hr on takeoff.  (From my research on the forum here, that seems to be the correct value, approximately)  Takeoff power felt normal, and probably a bit stronger than the old engine, and I suspect my old engine was down a bit on performance, so a bit higher fuel flow isn't terribly surprising, but I didn't expect that much more flow.

Anyway, based on this, I suspected that my full-rich mixture setting is a too rich.  So I repeated the mag check with the mixture slightly pulled back, and the mag checks were totally normal.  I also noted the full-rich runup RPM (2000) fuel flows were also higher than the old engine.  I suspect the fuel flows are higher across the board.

Based on my reading, this is basically not adjustable... so I think it's potentially an issue with the fuel servo and I guess I need to contact the engine shop for their opinion?

Were the mags overhauled? If so, who did them?

[PT20J]

I assume that the engine shop had the servo overhauled or supplied an overhauled servo. Perhaps it was set up incorrectly. The servo needs to be set to Lycoming specs on a flow bench - there isn't a field adjustment. I usually see about 18.5 gph. on my A3B6. 

 

[EricJ]

20 gph sounds a bit high, but if it is running well and climbing well I'm a bit puzzled.   Does it make static rpm on the ground at full rich?

If it is too rich it could be either the servo was not properly overhauled, or the injector nozzles are not the correct size.   There aren't any field adjustments to correct either.

 

[Ryan ORL]

2 hours ago, LANCECASPER said:

Were the mags overhauled? If so, who did them?

Yes, all my accessories were overhauled.  The mags were overhauled by Quality Aircraft Accessories.

[Ryan ORL]

1 hour ago, PT20J said:

I assume that the engine shop had the servo overhauled or supplied an overhauled servo. Perhaps it was set up incorrectly. The servo needs to be set to Lycoming specs on a flow bench - there isn't a field adjustment. I usually see about 18.5 gph. on my A3B6. 

 

Yes, the servo was an overhaul exchange unit from Avstar Fuel Systems.  I am guessing it was configured incorrectly.

[Ryan ORL]

1 hour ago, EricJ said:

20 gph sounds a bit high, but if it is running well and climbing well I'm a bit puzzled.   Does it make static rpm on the ground at full rich?

If it is too rich it could be either the servo was not properly overhauled, or the injector nozzles are not the correct size.   There aren't any field adjustments to correct either.

 

It does make full static RPM, even when full rich.

I'm guessing it might be not the right size nozzles... we'll see what the engine shop says.

[PT20J]

I believe all Lycoming normally aspirated engines use the LW-18265 nozzles. That's a Precision Airmotive 2524864-2 or AvStar AV2524864-2.

[Shadrach]

The servo was likely set on the high side of or out of spec when overhauled. Curious what your take off EGT numbers look like (I’m betting low 1100s). That FF would not concern me on a 15° morning in the mid-Atlantic…but in Orlando, it’s a little too much of a good thing. That being said, if I were the only one flying the plane, I’m not sure I’d pull the servo off over it if a turn or so on the mixture knob will bring things in line.

[N201MKTurbo]

You can always reduce the fuel flow with the red knob. With the RSA-5 you have no way to increase it.

If your FF gauge is accurate, just roll the fuel flow back to 18.5. I normally don't recommend leaning on takeoff or climb, but you seem to have bonus fuel. 

[ArtVandelay]

I would verify FF readings by filling the tanks, then refill and compare to engine monitor data.

[PT20J]

First, I’m assuming that no changes were made to the fuel flow measuring system from the old engine that measured 18.5 and the new engine that measures 20.5 gph. If true, then it’s an apples-apples comparison and the original 18.5 is reasonable for a 200 hp IO-360.

Second, if the fuel flow at full power airflow is off, I would be concerned that the wrong calibration chart was used. Lycoming sets the specs and there are several variations. Each calibration chart has I believe 4 calibration points. These are set by changing parts in the fuel metering unit while using a flow bench.

You can check that you have the right injector. According to Lycoming SI 1532M, the IO-360-A3B6 should use an AvStar AV2524054-11. 

[Ryan ORL]

5 hours ago, ArtVandelay said:

I would verify FF readings by filling the tanks, then refill and compare to engine monitor data.

Going to do that this week because I’m sure that sensor was touched during the install.  It was previously accurate to within less than half a gallon over a 50 gallon burn.

[Ryan ORL]

4 hours ago, PT20J said:

First, I’m assuming that no changes were made to the fuel flow measuring system from the old engine that measured 18.5 and the new engine that measures 20.5 gph. If true, then it’s an apples-apples comparison and the original 18.5 is reasonable for a 200 hp IO-360.

Second, if the fuel flow at full power airflow is off, I would be concerned that the wrong calibration chart was used. Lycoming sets the specs and there are several variations. Each calibration chart has I believe 4 calibration points. These are set by changing parts in the fuel metering unit while using a flow bench.

You can check that you have the right injector. According to Lycoming SI 1532M, the IO-360-A3B6 should use an AvStar AV2524054-11. 

Correct, no changes.

Seems like it’s the right unit at least.

[Ryan ORL]

6 hours ago, Shadrach said:

The servo was likely set on the high side of or out of spec when overhauled. Curious what your take off EGT numbers look like (I’m betting low 1100s). That FF would not concern me on a 15° morning in the mid-Atlantic…but in Orlando, it’s a little too much of a good thing. That being said, if I were the only one flying the plane, I’m not sure I’d pull the servo off over it if a turn or so on the mixture knob will bring things in line.

That’s a pretty good guess, I definitely saw around 1150 I want to say, but I will go pull the SD card tomorrow and take a look.

[Ryan ORL]

On 3/11/2024 at 5:21 PM, Shadrach said:

The servo was likely set on the high side of or out of spec when overhauled. Curious what your take off EGT numbers look like (I’m betting low 1100s). That FF would not concern me on a 15° morning in the mid-Atlantic…but in Orlando, it’s a little too much of a good thing. That being said, if I were the only one flying the plane, I’m not sure I’d pull the servo off over it if a turn or so on the mixture knob will bring things in line.

I did a small calibration test on the fuel totalizer… through about 16 gallons it was off (high) between 3-4%.  So not perfect but pretty close.  I will run a better calibration soon on a larger sample.

So I pulled my most recent takeoff log…

Max fuel flow hit 20.7 gal/hr (29"/2690 rpm).  If my quickie calibration is roughly correct, that would correspond to around 19.9 or 20.0.

EGTs were in the 1160-1180 range for the most part.

My plan, I think, is to fly it this way and maybe dial the mixture knob back one turn or so to aim for around 19 on takeoff.  Meanwhile I will see what the engine shop thinks.  I’m reluctant to mess with anything else until annual probably, which is coming in a little over a month.  I will finish the break-in within the next week or two, I hope.

[Shadrach]

7 hours ago, Ryan ORL said:

I did a small calibration test on the fuel totalizer… through about 16 gallons it was off (high) between 3-4%.  So not perfect but pretty close.  I will run a better calibration soon on a larger sample.

So I pulled my most recent takeoff log…

Max fuel flow hit 20.7 gal/hr (29"/2690 rpm).  If my quickie calibration is roughly correct, that would correspond to around 19.9 or 20.0.

EGTs were in the 1160-1180 range for the most part.

My plan, I think, is to fly it this way and maybe dial the mixture knob back one turn or so to aim for around 19 on takeoff.  Meanwhile I will see what the engine shop thinks.  I’m reluctant to mess with anything else until annual probably, which is coming in a little over a month.  I will finish the break-in within the next week or two, I hope.

I had my servo overhauled in the mid aughts by a local fuel system specialty shop. I asked the mechanic to request that the tech set my servo at the max permissible fuel flow for the application. Prior to overhaul my egts were in the mid to low 1200 range. Upon reinstalling the newly overhauled servo egts dropped about 50° into the low 1200/high1100 range. Which made for very cool CHTs at cruise climb (typically 310° to 330°) even in summer.  My airplane never ran hot for sale, but since the servo rebuild, I’ve never found myself wanting for more fuel flow to aid cooling. I wish I could tell you our take off fuel flow, but I am just getting around to installing a fuel totalizer. All the above being said, I would definitely make sure the reading is dead on before pulling the servo.  The mag drop is odd, are you seeing issues with specific cylinders when running single mag? 

[EricJ]

10 hours ago, Ryan ORL said:

I did a small calibration test on the fuel totalizer… through about 16 gallons it was off (high) between 3-4%.  So not perfect but pretty close.  I will run a better calibration soon on a larger sample.

So I pulled my most recent takeoff log…

Max fuel flow hit 20.7 gal/hr (29"/2690 rpm).  If my quickie calibration is roughly correct, that would correspond to around 19.9 or 20.0.

EGTs were in the 1160-1180 range for the most part.

My plan, I think, is to fly it this way and maybe dial the mixture knob back one turn or so to aim for around 19 on takeoff.  Meanwhile I will see what the engine shop thinks.  I’m reluctant to mess with anything else until annual probably, which is coming in a little over a month.  I will finish the break-in within the next week or two, I hope.

Those EGTs are about where mine were when my servo was freshly overhauled and my JPI (and EGT probes) were brand new.    EGT temps are dependent on where the probe is in the stack, which can vary from airplane to airplane, so aren't really comparable, but at least EGTs like that aren't unheard of.

So I wouldn't even bother leaning on takeoff unless you're at high DA or have some compelling reason to do so.   It may all be working correctly and might settle in to something else as it gets used.   My servo and JPI are over five years old and now the EGTs are high 1200s or more on takeoff and climbout.    Still runs fine.

[Shadrach]

6 hours ago, EricJ said:

Those EGTs are about where mine were when my servo was freshly overhauled and my JPI (and EGT probes) were brand new.    EGT temps are dependent on where the probe is in the stack, which can vary from airplane to airplane, so aren't really comparable, but at least EGTs like that aren't unheard of.

So I wouldn't even bother leaning on takeoff unless you're at high DA or have some compelling reason to do so.   It may all be working correctly and might settle in to something else as it gets used.   My servo and JPI are over five years old and now the EGTs are high 1200s or more on takeoff and climbout.    Still runs fine.

It’s true that probe placement affects raw EGT numbers. It’s also true that the peak EGT number for a cylinder has little variation between cruise and max power settings.  It would be pretty easy to ballpark how far ROP each cylinder is at full rich. I would bet that all cylinders are between 250° and 300° ROP.  If any cylinder is richer than that, I’d consider having the servo adjusted. I’ve flown several Lycoming’s that have cylinders in the 200ROP range at full rich. That’s ok, but I prefer a bit more fuel flow.