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Rotec TBI issues

UH1CW2

Well Known Member
I just installed a new Rotec TBI unit on my aircraft. It was carbureted but I wanted to clean up the lower cowl area and install a 90 degree elbow to mount the ROTEC TBI to. I am talking about a RUTAN LONG EZ. I need this forums help with troubleshooting the issues. The unit seems to be starving the engine of fuel. I checked flow prior to the diaphragm. it was almost 20 GPH. I have checked the finger screen and it is clean. The unit will not allow the plane to idle below 900 RPM I need to have the mixture FULL RICH and the throttle open about 20%. The engine is chugging and stumbling like it is too lean. If I attempt to pull the mixture even a little bit off full rich the engine will die at any RPM. the 0320 runs extremely rough and struggles to maintain any RPM without choking for fuel. I was able to get 2400 static out of it today but I could not move the mixture lever off full rich or it would start popping and chugging for fuel. Even at 2400 WOT the engine was running like it was way too lean. It has a lightspeed electronic on the top and mag to support bottom ignition. I am running 100LL AV gas. When it was carburated it ran like a clock at any RPM, smooth.

[email protected]

Does anyone have any experience with the ROTEC TBI on a Lycoming engine. I need your help to resolve this issue. I have plenty of installation pics to review. I have a ROTEC 40-4 unit.

Respectfully,

Phil Camarda
 
Same problem here.

I had the same trouble with the rotec unit, and it got much worse after the fuel regulator was overheated by a nearby exhaust pipe. (Heat soaked while parked) it ran poorly after that. Is your exhaust near the regulator? Also, I asked for tech help and a price for parts to rebuild the regulator twice now and no response, so I've changed to a Marvel carb, old school but runs great.

Lance
 
Additional information

I am running the standard Lycoming low pressure pump 3-4 PSI and the FACET electric pump 2-3 PSI. I was told by ROTEC that they will operate on .5 to 10 PSI without issue. I just do not understand why the unit is running so lean at every RPM. I mean the mixture is WIDE OPEN or it will not keep running. I was told that these units are a design improvement over ELLISON units?
 
Email Rotec

Email their techs with a description of the problem and they usually get back to you within a day. Big time difference. They have been very quick to answer questions I have had. You can message they from their web site.
 
Spoke with ROTEC

Seems they do not have customers send back units like mine. instead they tell me to take the entire unit apart and inspect the inside for any lapping/polishing compound they may have left behind. They also said that they know they have this issue with Lycoming units 40-4 & 4/5 due to clogged spray bars and or idle path ways. this is caused by factory assembly of the unit with debris and lapping compound left in them. They also have issues with the wrong spring length in the regulators causing lean condition. To be honest I find this company to be out of the business selling parts at 1000 dollars if they do not work and expect the customer to troubleshoot and fix the issues. Not very happy with ROTEC at this time. Tomorrow will be a take down of the entire installation and a disassembly process of the entire unit. Should be a great day in the 95 degree wet Mississippi heat !

By the way, thank you for your help I do appreciate any comments that I received with this issue. I will post my findings in a day or so.



Respectfully,

Phil Camarda
 
I have the Rotec TBI on my Pitts S1C. I had a similar problem when first intalled because it would not idle. Had to send back to the factory (paying the postage both ways), and they fixed the idle circuit. Ran fine for about 10 hours when the diaphram in the regulator had a leak--this you could tell because of fuel in the clear sense tube. After some back and forth--they wanted me to press the rivet more in the diaphram, and I wanted a new diaphram--I got my way and they sent the new diaphram. I have about 20 more hours on it with no problems. With a Pitts, 30 hours a year is pretty frequent flying.

If you can hang in there with their service (which happens but is not spectacular), the units run really good. Rotec is a small company it seems, and they have had their issues with their products (including some with their radial engines). But all that, I am still a fan of their products and I like their TBI.

Another issue (minor IMHO) that I have had, which is also a problem with the Ellison TBIs (now no longer made) is that the idle mixture changes with the seasons. Mine will idle wonderfully at 650 RPM when the engine is warm, but in the winter (such as it is in Sacramento, CA) Until the engine in warm, I have to keep the RPMs up or the engine will die. Once the engine is nice and warm--idles great. This means that in the winter, the startup and taxi to takeoff requires higher RPMs to keep the engine running.

I really like the primer button on the diaphram for starting when cold. Works great. No need for primer circuit like is required for the Ellisons. I use a bicycle cable arrangement to actuate.

If you are not doing acro, and space is not a problem, then yes a carburator is probably less problems, but in my situation, I really like the Rotec TBI, and I don't have a problem dealing with the idle in the winter.

BTW, I am putting a Rotec TBI on my RV-4. FWIW.....
 
You mentioned you have a 90 degree elbow...it could be that the airflow turbulent enough that the fuel is not being drawn out of the spraybar.
 
UNIT RUNNING on ENGINE

I took the unit off the plane this morning and brought it home to the shop. Took everything apart as instructed by ROTEC. Found the following issues:
  • Diaphragm spring too long. .698 cut to .605
  • Gray lapping compound in the idle fuel circuit
  • Gray lapping compound in the main fuel delivery chamber
  • holes in spray-bar not completely open
Cleaned everything with TBI spray cleaner, Blew all passages with air, opened up spray bar holes with a needle and reassembled. Installed TBI back on aircraft and it is now running as designed. On a positive note: I picked up 190 RPM on static run up. It was 2490 when carbureted now 2680. Need to make some small adjustments to the idle screw. I can not supply any other information until the wings go back on and I can get it in the air (about 2 months).

I want to say thank you to everyone who posted. Any advice and or assistance is always greatly appreciated.

Phil Camarda
www.LongEZPilot.com
www.Selectfirellc.com
 
Phil,

Did you have detailed instructions from Rotec, or "Just take it apart, clean it up and reassemble?"

If detailed instructions, any chance you could post them here?

I have one that will be installed soon, and am thinking that a preemptive cleaning may be a good idea.

FYI, Rotec will be at Oshkosh this year, booth 627 in north display area. 200 feet north of Van's booth.

Tony
 
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On a positive note: I picked up 190 RPM on static run up. It was 2490 when carbureted now 2680.

This may not be a positive note. :( Think about it. What data did you collect at the time? Fuel flow and EGT and what CR is your engine?
 
This may not be a positive note. :( Think about it. What data did you collect at the time? Fuel flow and EGT and what CR is your engine?

Huh? He's running stronger and likely burning more fuel at full rich.

Phil is the right spring length 0.605"?

I just converted 55BC over to a Rotec and am waiting on a throttle cable from Spruce. It was a bit of a pain due to some of the head scratching and fabrication involved but I've come up with a very nice and clean installation.
 
E:mail from ROTEC

He did send me a complete breakdown drawing of the TBI and Regulator. its a PDF file I can forward directly to you as I do not know how to post it here.

From: Cuinn Herrick [mailto:[email protected]]
Sent: Monday, June 30, 2014 12:48 AM
To: [email protected]
Subject: RE: Rotec TBI

Hello Phil,

Thank you for your email and your call this afternoon.

Please see the following FAQ for more information on lean running TBI?s: http://www.rotecaerosport.com/faqs/tbi-lean/

Based on our phone conversation, I am going to get you to perform the following checks periodically. For your reference, see attached for TBI and regulator exploded assembly:

1. Ensure the length of the regulator flow spring is correct: http://www.rotecaerosport.com/faqs/tbi-regulator-flow-valve-spring/

2. Ensure the spray bar and idle circuit are clean http://www.rotecaerosport.com/faqs/tbi-spray-bar-cleaning/. I will get you to go further than the advisory recommends and remove the spray bar from the body.
a. Be careful not to damage any of the seals when removing the spray bar. The spray bar is removed by pushing out the 2 roll pins. These can be reused for reinstallation so do not damage them.
b. Check the bore of the spray bar thoroughly. A small bottle brush may be required to get behind the taper on the end of the bar.
c. The idle circuit can be cleaned at the same time by removing the idle screw and flushing it out. http://www.rotecaerosport.com/wp-content/uploads/2012/01/TBI-40-idle-ciruit-cut-away.jpg

3. Once these check have been performed we will consider spray bar modification as a last resort http://www.rotecaerosport.com/faqs/tbi-spray-bar-modification/

In regards to other O-320 user, my record show 53 currently using the TBI. You can be rest assured the TBI works with your engine. With persistence I believe we can get the unit to work with your installation like it has for many others, as we will continue to work with you.

I hope this information is helpful. If you have any further technical questions, do not hesitate to ask as I?m always here to assist you. Otherwise I look forward to your reply.

Kindest regards,
Cuinn Herrick
Mechanical Engineer

Rotec Aerosport Pty. Ltd. | ABN: 68 158 018 921 | Hangar 12, 86 Stuart Rd, Tyabb Airport, Tyabb, VIC, Australia, 3913
Email: [email protected] | Web: www.RotecAerosport.com | Ph: +61 3 5977 3805 | Skype: cuinnton
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ANSWER QUESTIONS

The spring lengths are given as .59 to .67 The longer the spring the leaner the unit will run, Shorter spring More fuel flow. I did not take any engine data as the airplane is a pusher and I have no way to cool the engine cylinders Cant fly, wings are off. However, I do have a GRT EFIS and can record all engine data as it is fully instrumented. The last E:mail I received from ROTEC stated that they had moved to a new facility and hired many new people. They are addressing the quality control issues from this recent change.

My unit was built back in March or April of 2014 if this helps anyone who recently purchased one.
 
Huh? He's running stronger and likely burning more fuel at full rich.

Phil is the right spring length 0.605"?

I just converted 55BC over to a Rotec and am waiting on a throttle cable from Spruce. It was a bit of a pain due to some of the head scratching and fabrication involved but I've come up with a very nice and clean installation.

Gidday Bob,

Running stronger?.yeah most likely. But as for burning more fuel how can you be sure.

Big assumption. Without data that could be a very bad assumption.
 
Does anyone have any experience with the ROTEC TBI on a Lycoming engine. I need your help to resolve this issue. I have plenty of installation pics to review. I have a ROTEC 40-4 unit.

Hi Phil,
I've been running a Rotec TBI on a Lycoming O320-E2D in a Glastar for a bit over a year now, so far no issues. I replaced a carb, and the TBI starts much easier using the fuel regulator override than the primer system and carb combo ever did. I have not noticed any significant fuel use or performance differences, however I only recently have installed a fuel flow sensor so I don't have anything to compare from when I was running the carb.

I am just using gravity for the fuel feed, no mechanical fuel pump, but I did install an electric boost pump per Rotec's recommendations for aggressive, high nose takeoffs. Having said that, I don't normally use the fuel boost pump and haven't found any need for it yet, even with high nose attitudes (tested at altitude, of course). I anticipate only using it if I were taking off from a short field requiring a max performance takeoff.

-Dj
 
Right now I've got a few ground runs on the Rotec and its been running very smoothly. In the air in a few days after resolving a few other maintenance issues. So far I'm noticing the primer button is not necessary. If one opens the throttle and turns the boost pump on for a few seconds before start the engine is effectively primed. To shut the engine down, you just go full lean then bump the throttle open.

Very pleased with the smoothness so far.
 
Starting the ROTEC TBI

I agree with the priming procedure, just open the mixture and turn on the boost pump and the idle circuit primes the unit after about 5 or so seconds. I did install a lever on the priming unit so I could pull a cable and manually prime the TBI. However, that is coming out and I am installing a Small Euro door lock motor with 8 Kg force to open the primer unit by pulling the lever I installed. Its a 12 Volt unit and it is about the size of a large Key-Fob. I know that I may not use it very often but in the event I need to prime the engine with a bit more fuel in the winter time it will be available to me.

I have to say that the unit does run very nice even with the light weight wooden prop I am running. Idle speed must stay above 700 to keep everything smooth. But again that is because I have no mass at the end of the crank, just a light weight wooden 2 blade prop.

Phil
www.longezpilot.com
 
First flight with ROTEC

After I leveled off in the traffic pattern at about 140 kts I started to pull the power back, I noticed the engine started running extremely rough while reducing throttle. Then I decided to pull Carb heat and pull the power back. everything was fine. It wasn't carb icing. I determined that the ROTEC does not like RAM air at all. If you exceed the engines intake needs with RAM air the fuel does not flow out of the bar that runs across the TBI's throat. I have cut the scoop off the bottom of the airplane. At this time I will just use a standard 3 inch wide NACA about 3/4 inches deep. I will fly it again tomorrow to determine if removing the 3 inch half moon scoop from the bottom of the plane solved the pressurized air / fuel flow issue. Other than that it seems to idle great and start immediately. Performance in the climb was exceptional I have no other complaints.

Phil Camarda
 
After I leveled off in the traffic pattern at about 140 kts I started to pull the power back, I noticed the engine started running extremely rough while reducing throttle. Then I decided to pull Carb heat and pull the power back. everything was fine. It wasn't carb icing. I determined that the ROTEC does not like RAM air at all. If you exceed the engines intake needs with RAM air the fuel does not flow out of the bar that runs across the TBI's throat. I have cut the scoop off the bottom of the airplane. At this time I will just use a standard 3 inch wide NACA about 3/4 inches deep. I will fly it again tomorrow to determine if removing the 3 inch half moon scoop from the bottom of the plane solved the pressurized air / fuel flow issue. Other than that it seems to idle great and start immediately. Performance in the climb was exceptional I have no other complaints.

Phil Camarda
If all works out well could I get a photo of the change you made to the
Cowl? I'm very interested in what you had to do to get satisfactory results.
 
NYTOM answer

I will let you know everything that I have done to get the ROTEC to perform as advertised. I am waiting for the temp and humidity to settle down today. Its like I live in thunderstorm alley here in Mississippi.

To try and describe the setup I have: I have a long EZ (engine in the back). So I added a 3 inch wide by 9 inch long NACA duct to the bottom of the airplane skin. That NACA feeds into a 2.5 inch sceet tube that enters my Carb air and heat box. Then it goes directly into the throat of my ROTEC TBI. I wanted to make sure I got enough air into the TBI so I added a 3 inch wide by 2 inch tall oval scoop at the base of the NACA scoop. The naca looked like a conventional RAM air scoop and functioned like one as well. Kind of defeating the purpose of the NACA scoop. I just wanted to make sure I captured enough air. Well, I have cut that half moon ram air scoop off the base of the naca and now it is just a standard 3 x 9 x3/4 deep naca scoop feeding the same 2.5 inch sceet tubing to the airbox and TBI.

Once the weather clears up I will take her up again and see if removing the RAM air scoop reduces the inlet air pressure enough so the TBI will flow correctly at all throttle positions at all speeds. I will be posting pictures and updates on my web site.

Phil Camarda
http://www.longezpilot.com
 
Hi Phil,

If you were getting too much RAM air does this mean that you were running too lean and that is why it ran rough? I see there is a procedure to increase the size of the jet holes from .012 to .016 to let more fuel flow. Or would the next size larger TBI work better to get you enough fuel to match the air flow? Considering the ROTEC TBI for my RV-6A with O-360 engine.
 
TBI requirements

The TBI must draw air past the fuel bar. If the Manifold pressure goes positive or exceeds the engines optimum air/fuel ratio with pressurized air the TBI will run lean. It's my fault as I am not using a standard airbox and filter as the recommendations state. I just do not have the room in my cowling for an additional air filter system. If I had a filter assembly in front of the ram air I would most likely be OK. The unit will or should work great once I go to the low pressure recovery NACA and remove direct non-defused RAM air from it. If Not I'll have to install a filter/defuser screen.

Phil Camarda
http://www.longezpilot.com
 
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Phil,

I managed to get a NACA inlet, filter, flow straightener and Rotec to fit behind the Jab 3300 going into my Panther. The Jab is a bit unusual with its rear-facing carb. Link to photos here.

Might be some ideas you can use there.

Tony
 
Phil,

I managed to get a NACA inlet, filter, flow straightener and Rotec to fit behind the Jab 3300 going into my Panther. The Jab is a bit unusual with its rear-facing carb. Link to photos here.

Might be some ideas you can use there.

Tony

Tony,

In reviewing your photos on the fuel pump....did you make the same AN conversion replacing the barbed fitting on the carb?

Great idea...will put the fuel pump mod on my hit list.

Regards,
 
Tony,

In reviewing your photos on the fuel pump....did you make the same AN conversion replacing the barbed fitting on the carb?

Great idea...will put the fuel pump mod on my hit list.

Regards,

No more Bing. Replaced with Rotec, which has AN6 fuel fitting.

Tony
 
nice job

Your setup looks great. you will have no issues at all with the induction system. Should run like a champ first start. By the way, nice job.

Phil
 
Flew today and can't run WOT without surging/running too lean. I have a nice CNC machined spacer on the bottom with a honeycomb straightener using the same stuff Tony used. Spring is the correct length and everything is clean. Am going to enlarge the holes tonight with a #80 drill.
 
Flew today and can't run WOT without surging/running too lean. I have a nice CNC machined spacer on the bottom with a honeycomb straightener using the same stuff Tony used. Spring is the correct length and everything is clean. Am going to enlarge the holes tonight with a #80 drill.

Pooner,

Whoa up on drilling holes out. When I was running an Ellison I saw same thing as you. Fix was a throttle stop about 3/8" shy of WOT.

Tony
 
I have read that and don't find that to be a good fix. I have three rotecs on hand, no problem drilling out the holes and doing a bit of experimentation to get things correct.
 
I have read that and don't find that to be a good fix. I have three rotecs on hand, no problem drilling out the holes and doing a bit of experimentation to get things correct.

I assume you have the 48mm TB? If yes, it's designed for 165-250 hp engines with a displacement of 360-540 cu in. If you're running it on an O-360 there's too much area at WOT. If it's a 40 mm unit, then nevermind.

Tony
 
Sleepy these things are engineered to be in the ballpark. In fact I have the first 48. I gave them the dimensions of a RSA-5 and the rest is history so I expected some experimentation. Tonight a friend of mine came over and helped me run it before removing the TBI for enlarging the holes. Without a doubt it is running perfect in the first 2/3rds of opening and running lean above that. Pulling the mixture in the middle of the range where the double row of holes starts results in an immediate drop in EGT and RPM, which can only be too lean. At WOT throttle it stumbles occasionally and the mixture pull immedately reduces RPM and EGT...only talking 1/8" or so pulling on the mixture. I've already opened up the four row and two row sets of holes to 0.016", and will try to get the unit back on tomorrow.
 
2nd test flight

After climbing to 1000 AGL in the traffic pattern at about 144 kts I pulled the power back to mid throttle and the engine did the same thing. this time I was able to pull about half throttle, so it was a little better. I then pulled carb heat and everything was OK I was able to pull the throttle to idle. So, I have decided that I will leave the NACA scoop the way it is and put a flapper valve in the intake SCEET tube. The dedicated induction path to the TBI will just dump any excess incoming NACA air into the engine cowlings and it will exit out the back with the cylinder hot air. I'll try to get this done by the weekend and post findings.
 
Hi Bob,

Can you post some pics of your installation? Did you use the Vans air box?

I'll post some pics when I get everything working as desired. Ready for another run tonight with three stages of holes from WOT enlarged with a #78 drill bit.

Using Van's airbox on an existing installation replacing a MA4-5. I had to machine a plate to match a spacer/flow straightener attached to the bottom of the Rotec which is 2.225" tall. When I put the cowl on the airbox fits the snout perfectly. I have Solidworks part files for everything including the mixture arm, spacer/flow straightener and bellcrank assembly.
 
Thanks Bob! Sounds like your installation is what I would use on mine. I wonder if the diameter of the hole in the spacer could be reduced from 48 to maybe 44 to reduce the flow of air if it is getting to much air and the enlargement of the pin holes doesn't work.
 
The idea to limit the travel of the of the throttle or otherwise limit airflow is a kludge. At any given throttle position with fixed holes metering fuel, if it runs too lean at a given opening position then the holes from there on up need to be enlarged. Its simple to verify whether its too lean at a given position or not by leaning and watching what the EGTs do.
 
Long EZ Flight 3

Well after providing a flapper port in the sceet hose between the heat box and the NACA duct everything seems to work fine. Any pressurized air just flows out of the flapper valve and the TBI uses what it needs at all RPMS. I believe the problem is solved. Moving on to finishing the cowling body work and paint. I have been working on it a bit at a time I think October is a good month to shoot paint on the upper and lower cowlings, gear legs and nose of the aircraft. I like the ROTEC so far!

Phil Camarda
http://www.longezpilot.com/N55GR%20page13_files.htm
 
The idea to limit the travel of the of the throttle or otherwise limit airflow is a kludge..

That makes sense Bob. So if this TBI was on a O-540, that it is supposed to works on, wouldn't the problem be even worse as the O-540 would require 50% more fuel?

Looking forward to hearing your results.
 
Just validated my changes were correct. No more stumble at WOT and the engine ran well on the ground. Might go a drill size up on the same holes after I do some flight testing.
 
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That makes sense Bob. So if this TBI was on a O-540, that it is supposed to works on, wouldn't the problem be even worse as the O-540 would require 50% more fuel?

Looking forward to hearing your results.

Perhaps. But I have the CNC equipment to fabricate a different spray bar. Really just a matter of adding more spray holes.
 
Bob;
I was just realizing that the air flows thru a round tube, so the increase in the area of the opening is exponentially less as you approach full open.
The holes would need to be opened a lesser amount as the throttle approaches full or you may experience a rich condition? (@ wide open throttle)
You probably already took that into account but didn't mention it?
 
What I have been doing is running it in steps of about 1/4" of throttle opening and noting what kind of EGT change occurs when pulling the mixture. It is quite possible that at WOT only a few holes, if any, need to be enlarged.
 
Flew for 45 minutes tonight. Still a bit on the lean side across the board, and will enlarge the holes I did not yet enlarge and will go next drill size up on the four row holes, perhaps not all of those will be enlarged. WOT just an occasional very slight shudder, and still haven't calibrated the fuel flow. Throttle response is good. Seeing 29" of mp on takeoff, the only time I've ever seen that was flying a Rocket with an RSA-10 and cold air induction. Definitely running strong and smooth. Did a few touch and go's and rapid throttle movements over the airport.

Running 2300-25" for cruise the throttle opening is not quite half open. So the holes I haven't yet enlarged will go up a size.

Won't fly again until Sat. after I do the next round of hole enlarging, and will then do some higher altitude tests.

I'm also going to add another roll pin to the slide/rod. The throttle is harder to move due to friction. Its not bad at all, but I'm concerned about stressing the one roll pin while flying formation.
 
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conquered.

Ended up enlarging the lower half holes to 0.016" and the four row holes to 0.018". Running great, no more lean issues. Flew 2.0 hours today.

At takeoff 2700 RPM 29" burning 12.8 GPH. Did some 100kt climbs and cylinder temps don't go over 400. Leaning from there causes a peculiar bump up to 14.5 GPH with a subsequent rapid cooling of EGT's and CHTs as expected. Not sure if this has to do with the 0.018" being covered by the throttle plate since the fuel flow bump starts with the throttle closed about 1/2". Its no big deal to take care of this with mixture and at this point consider it a feature to cool the engine if needed. Something odd happens to the airflow thru the rotec and more fuel gets sucked out of the spraybar when the throttle is partially closed.

All around running smooth with more power than with the MA4-5.

I'm finding that since the throttle and mixture are not interconnected the mixture requires more attention when changing power settings. No big deal.

Have not yet had to prime it to start.

Now the part I'm smiling about. The airplane has a O-360 and blended airfoil Hartzell. Running 2300-25" 3000ft 165kts 1375 EGT (around 20 deg. LOP) cylinder temps ~340. Oil temp 195. At that setting running 8.2 GPH all day long. According to Kevin Horton's O-360 spreadsheet this is 79% power. Pretty dang good.

Running 50 deg. LOP will show 7.9 GPH but will get an occasional stumble/burble. I need to try below 65% and at altitude.

Now that I consider the airplane safe with a few hours on it I'm going to start doing some test card testing particularly at altitude.
 
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Bob,

Great to hear you are refining the TBI, a fellow down here with a O-235 had to do the same sort of thing.

Just a tip,
Now the part I'm smiling about. The airplane has a O-360 and blended airfoil Hartzell. Running 2300-25" 3000ft 165kts 1375 EGT (around 20 deg. LOP) cylinder temps ~340. Oil temp 195. At that setting running 8.2 GPH all day long. According to Kevin Horton's O-360 spreadsheet this is 79% power. Pretty dang good.
That is 67-68% power not 79% and being LOP this makes perfect sense compared to a ROP setting.

Also,
Running 50 deg. LOP will show 7.9 GPH but will get an occasional stumble/burble.

Well that is hardly surprising. At such a MP and RPM being 50dF LOP is akin to starving it to death. The idea of 50dF LOP is a good number only ever applies to a power about 77-78% (when at a LOP fuel flow). No other time.

Hope that helps. :)
 
User Input Data
Pressure Altitude (ft): 3000
RPM: 2300
Manifold Pressure (in HG): 25
Temperature Units (F or C): F
Temperature (deg F): 72

Calculated Data hp (% power)
power at actual temperature= 142 79%
power at standard temperature - 20 deg F= 149 83%
power at standard temperature= 146 81%
power at standard temperature + 20 deg F= 143 79%
 
Bob,

You would be correct if you were running say 75-80dF ROP or more, but you weren't according to your post.

If you were LOP as you say, that calculation table goes out the window.

Depending on your CR which has a small impact the % power, what you had was as stated in my post above.

Think about why, and the clue to help here is when LOP by definition fuel flow determines the HP delivered. The graph below will help, and this can be assumed at any given MP and RPM.

Landmarksgraph_zpsbfb07cbb.gif


Hope that helps.
 
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