Disclaimer: I apologize if this is covered on another post but I have done the prereq searches, read all the previous posts, attended APS a few years back, and read the EAA articles but I still have a question and hoping to find an answer.

Specs: Maule MT-7-260 IO-540 260HP

I wanted to check and see if others were seeing the same engine ops as me. Normal cruise is 24" / 2400 and I see about 16-17 gph, 125 knots indicated ROP

Normally seeing ~380 cht and close to 1500 egt. Seems high but I just can't get it to drop without really reducing power.

I used to fly a conti 550 lean of peak for many hours with great results. Anytime, I even think about LOP in the lycoming it starts to bog down and reaallllyy lose power once I hit peak and I haven't had the cajones to go any leaner so I have just been staying rich.

My main concern is why the Lycoming stumbles so bad when trying to lean. I wanted to make sure I am doing something wrong and not that there might be an underlying problem with the engine that I should get checked out.

Thought I would ask in case I am doing something totally stupid.

Thank you.

I finally decided to post when I saw a comment from someone saying they cruise 2300/22" in a IO540 at 8-9 GPH Obviously I am doing something wrong.

I don't think I can see that unless I get down around 1500rpm...

Spent ten years with a normally aspirated Aztec - 2200/19 and LOP reliably produced 150knots TAS and 17-18 gph total - with a useful load of 1800 lbs it was a great machine. Would span the Mediterranean West to East (Zagreb) with ample reserves.

Unfortunately it attracted airways charges in Europe, so eventually was sold.

We are flying very similar engines, and our aircraft seem aerodynamically similar too.

For the ROP settings you describe, I also see 125kts exactly.

LOP 2300/22" 9gph drops me back to 108kts consistent. 8gph is more like 104kts (still the most efficient!).
I am missing some fairings and expect >110kts consistently in the near future. Until bushwheels happen....

I also see a rapid drop-off in power as you transition past the peak, this is normal. Mine will sometimes run rough if I lean back below 8.4 in normal certain operations. If I descend from altitude and the engine leans itself very very slowly, I get get smooth running as low as 7.4gph.

I normally drop back to 20", run the mixture back *fast* until the engine starts to fumble slightly, then enrich *just* until it runs smooth - from here I know I am LOP (with my engine!), then increase up to 21" or 22" depending what altitude I am at, watching fuel flow and EGT closely to ensure I don't creep over the peak into the 'high-risk' area.
You may note that lower RPM gives cooler EGTs, if you deviate from 2400, this is normal.

Your engine will run a LOT colder LOP, which is a good thing. More like 320-360 F. Don't worry what your EGT actually likes to settle at, as long as it's consistent. Each plane is different for a whole bunch of reasons. You may notice peak EGT is colder at higher altitudes.

If you don't already have 'GAMI' fuel nozzles, the first thing you need to do is a so-called "GAMI lean check": 1. Reduce power to a safe level, well below 60% e.g. 2400/20",
2. Run the mixture back near to peak.
3. Very, very slowly lean over peak. Note the fuel flow the first cylinder peaks.
4. Continue leaning very slowly, giving time for the engine to respond. Note the fuel flow the last cylinder peaks at.
5. If the spread is more than 0.5gph between the first and last peak, then you may need balanced injector nozzles before LOP is a realistic option for you. If the spread is less, then you should be sitting pretty.

Battson, thank you very much for the info. That is exactly what i was looking for. Weather looks good tomorrow and i am planning on doing some tests.

On another note, i did some extensive traveling a few years back after college and New Zealand is hands down my favorite place i have ever been. What an amazing place to live and fly, i can only imagine what it is like in a bearhawk.

Thanks again

Texmaule wrote:Disclaimer: I apologize if this is covered on another post but I have done the prereq searches, read all the previous posts, attended APS a few years back, and read the EAA articles but I still have a question and hoping to find an answer.

Specs: Maule MT-7-260 IO-540 260HP

I wanted to check and see if others were seeing the same engine ops as me. Normal cruise is 24" / 2400 and I see about 16-17 gph, 125 knots indicated ROP

Normally seeing ~380 cht and close to 1500 egt. Seems high but I just can't get it to drop without really reducing power.

I used to fly a conti 550 lean of peak for many hours with great results. Anytime, I even think about LOP in the lycoming it starts to bog down and reaallllyy lose power once I hit peak and I haven't had the cajones to go any leaner so I have just been staying rich.

My main concern is why the Lycoming stumbles so bad when trying to lean. I wanted to make sure I am doing something wrong and not that there might be an underlying problem with the engine that I should get checked out.

Thought I would ask in case I am doing something totally stupid.

Thank you.

Let me tell you a story!

Anything over 1400° you will probably start going through exhaust flame tubes every 200 hours. Just plan on doing them. They are like $80.00 a side. If you don't do a preemptive replacement you will ruin the can and have to spend like ????$800.00 a side?????

How do I know this????

I fly a Maule M7 B4B5 low compression 235HP. New exhaust, max EGT +- 1520 back off to 50° ROP.

Original factory mufflers. I always ran 50° ROP. Lots of crack repairs on the rear where the tail pipes connect. Yes they were set up loose for movement. 2 sets of flame tubes. Around 600 hours they were shit! I got pair #2

Now I am running consistently 1400°-1430° that is 90°-100° ROP. Another 250-300 hours flame tubes GONE!!! and I mean disappeared gone. Caught it before the cans got warped.

I had to put a re-manufactured engine in, that's another story. We checked the flame tubes at real close to 200 hours when we did the engine. They looked great. After 50 hours on the new engine, all full throttle, full rich. EGT around 1300° Now there is 250 hours on the tubes, it was time for annual. The flame tubes were GONE!!!!! both sides disappeared GONE!!! The cans were warped. Into the scrap heap.

Set #3 Maule has raised their price from like $400 a side to like $800 a side. I might be off a little on prices, but it was a huge increase, so much so I went to Tim's Aircraft for his super duper, mega, heavy duty, top the line stainless steel, special flame tube design, bla bla bla $2900.00 or real fucking close. My buddy Dave has them and they seem to be working well. So I spring for them. Not wanting to hurt them I start running religiously 1380°-1400° Max is 1550°

So a month ago at annual I tell the AP IA, give those sum bitches a real good look. They have like 250-300 hours on them. The flame tubes all warped to shit! Back to California they go for flame tubes.

Tim is a great guy and the exhaust is top notch. Tim thinks I have a lean issue or air leak. I don't. No evidence on the spark plugs or anything else.

This is the conclusion I have come to. It is a flawed Maule design. The distance from the head to the muffler is to close. There is no time for the hot gases to cool at all. The SS material can't take the heat.

I know lots of guys running the same EGT as me, same engine, different brand of plane, completely different exhaust design, and they have no problems. Some exhaust even make TBO. The only difference I can see is 1.5 times longer pipes to the muffler. Some of the guys have the IO 540 and run LOP which makes the EGT even hotter. They seem to get away with it.

If you try to run the Maule exhaust LOP hot my bet is you will be buying exhaust sooner than later.

Remember the Maule exhaust is KNOWN!!! to spit the flame tubes, get the can cherry red, you pull the throttle back a little to fast and get a backfire, that blows a hole in the can and shortly there after you get a nice hole burned right through the cowling.

Good luck with the LOP with the Maule, Lycoming 540 combo.

Thanks OregonMaule for the insight.

What year is your Maule? Do you know if the exhaust system has changed from Maule over time or are they all the same?

Are you currently running below 1400 degrees now? Just backing off the throttle and prop and increasing mixture until you fall under those temps? I am guessing I would have to back off quite a bit and increase the mix in order to get EGT under 1400.

I've currently got 550 hrs on the plane so I am guessing I need to check with my mechanic to make sure he throughly checked the tail pipes and flame tubes...

Re 540 Lyc in Maules;

As I have suggested many times, the flame tubes should be checked every annual or hundred hours at the same time the U clamp SB is being attended to, so only a minute or two more work.
Please perform all SBs and SLs. They were written to help not hinder.

Rob, there is no way you can run the O540 B4B5 carburetted Lyc LOP as the spread of temps from first cyl to peak to last cyl to peak is far too much. (often 160+ degrees)

However, the IO540 W1A5(D) which can be tuned to a n EGT spread of 60 degrees can run LOP. without need for Gami.

The IO540 V4A5 can also be tuned to a small EGT spread.

70TG, check your fuel spider for fuel stains (cracks at fittings) it might be sucking air, intake tubes joints at oil pan and rubber sleeves.
If you have a scat tube running above the intake tubes on left side, it is compromising the cylinder cooling on left side.

Texmaule wrote:Thanks OregonMaule for the insight.

What year is your Maule? Do you know if the exhaust system has changed from Maule over time or are they all the same?

Are you currently running below 1400 degrees now? Just backing off the throttle and prop and increasing mixture until you fall under those temps? I am guessing I would have to back off quite a bit and increase the mix in order to get EGT under 1400.

I've currently got 550 hrs on the plane so I am guessing I need to check with my mechanic to make sure he throughly checked the tail pipes and flame tubes...

Mine is a 2000. I'm not sure about the exhaust if Maule has changed it. I doubt it. I am now keeping mine at 1400° or lower. Jeremy I agree you can not run a B4B5 LOP. I would never even try it.

Yes Texmaule do check your exhaust now. Like Jeremy says it is easy to do.

Cheers...Rob

u wont like the answer rob, but try some better fuel....car gas dont really get it...betcha lower temps 10-20 deg...also if u have movable cowl flaps, open up a notch...only run mine at 2400 rpm on takeoff...in cruise @ 21-22...only 5kts diff....fwiw...jomac

Does 92 octane run hotter than 100 octane in 7.2:1 engine?

i think it does Z...tougher to burn for the motor...not as clean...my 0-540 seems to stay pretty cool depending on the day...but i dont run cheap gas, or oil...just a thought...rob;s maule is a cool bird...! they do seem tighter cowled than the cessna stuff...that must be a factor...

Z, octane resists combustion so 92 should burn a little faster than 100. With EGT probes being located in the manifold, I'd assume that would show a cooler EGT since combustion would need less time to complete and would have more time to cool off.

92 would be easier for an engine to burn and should leave less incomplete combustion deposits (not to mention all that TEL) than 100LL.

jomac wrote:u wont like the answer rob, but try some better fuel....car gas dont really get it...betcha lower temps 10-20 deg...also if u have movable cowl flaps, open up a notch...only run mine at 2400 rpm on takeoff...in cruise @ 21-22...only 5kts diff....fwiw...jomac

I can tell absolutely no difference in 100LL and 92 UL NONE! My spark plugs never foul from lead.

Full rich WOT 1000MSL EGT is 1280° 27" MP. At 24" MP full rich same MSL the EGT goes to 1330° because there is less gas running through the engine.

I stand by my earlier post, it is a flawed Maule design period. Y'all can disagree, and I wish someone could show me how to stop my problem. I always listen.

I look at it this way. If I replace my exhaust at 600 hours. If I burn 500 hours of mogas at an average savings of $1.50 a gallon. Burn average of 14 GPH is 7000 gallons X 1.50 is $10,500.00 I guess I can keep buying $1600.00-$2900.00 exhaust systems. It still sucks.

Cheers...Rob

Rob,

Seems like a call to these folks might be worth it.

http://www.wemakeyoufly.com/news/maule-manufacturing-and-lees/

I'll check with them next time. Thanks

Ok so its not a 0-540 but my 0-470 runs amazing LOP, in fact it runs way better LOP in cruise than it does ROP as far as temps are concerned. All my EGTs are within 50 degrees and CHT's within 40 degrees and much tighter if it were not for #5 running al little hotter behind the oversized oil cooler, still #5 hangs about 345f. If u wanna really screw ur engine up run it 50ROP at high power settings

As the old adage goes "Lean it till it stumbles and come back in a turn or two till it smooths out" that is LOP on my 0-470, and all four 470's I have flown. I go a step further and after everything stabilizes lean a little more for desired temps. After running this way for well over 1000 hours in cruise in the last 3 years I'm convinced that all this BS'n about LOP being harmful is a total bunch of Bullshit. I flew a 0-540 recently and it ran great LOP, however I only flew it that way for a short period of time (10 mins) because the owners wanted it run super rich so thats what I did.

If your having issues running LOP you might consider getting new spark plugs or at least cleaning and gapping, bad plugs will cause the symptoms you describe. If I don't clean/maintain my plugs every 40 hours I notice a big difference in the tightness of all my temps. I've had plugs that checked out on the spark tester and were properly gapped n sparkling clean run poorly LOP, as soon as I replaced them with new ones problem solved. Rotating your plugs from top to bottom each cleaning is a good idea too.

Forgot to mention, timing is also an issue with LOP. If your timing is off there is a good chance that you will have problems with leaning. When we hung my current engine the mechanic that timed the mags the first time was off by four degrees, night and day difference, it would not run LOP and leaning out it would only make a couple cylinders peak and then get really rough and want to die. After we got the timing right runs LOP like a champ.

All good info, thanks everyone. Only running 100LL here in Houston. The timing or plugs could be the culprit. Skalywag, I may pull your ear at the Stol Roundup regarding your experience with this issue. With the JPI 700 I am able to watch the numbers pretty closely but I am having to run real rich in order to keep my temps normal.

maules.com wrote:The IO540 V4A5 can also be tuned to a small EGT spread.

In the interest of clarity, by EGT spread are you referring to the fuel flow spread between EGT peaks?

As I understand it, the absolute values of EGT (and their absolute spread) can vary from engine to engine because of difficulties with measuring it, and are kinda meaningless apart from as a trending / troubleshooting tool.