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Very narrow lean range. Need to ground a/c?

alpinelakespilot2000

Well Known Member
In the process of tracking down some high temps, I did a lean test through Mike Busch's Savvy Analysis Program. The lean range for my four cylinders are:
1-205F
2-222F
3-68F
4-62F
Test is conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.

Obviously, #3 and #4 are running really lean even at full rich. What concerns me is that if I'm running this lean at 6000 ft at 65%, how lean am I on takeoff while at lower altitude (1750 MSL) and at high power? Is it likely that #3 and 4 are in that range just rich of peak that should be avoided in order to avoid the risk of detonation? I'm particularly concerned given my #3 CHT can break through 400 in climb.

Savvy suggested checking for induction leaks on 3 and 4, and also commented that this could be the result of poor distribution on my carbed engine but, until I get that figured out, should I not be flying? Was headed to Arlington this week, but maybe not.:(

Thanks for the help. There are so many things I didn't think about before when flying planes without good instrumentation!
 
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You should be able to get a 150F or better EGT spread on all cylinders.
Induction leak is a good place to start. A can of ether is your friend.
Remember induction leaks are easily discernible at low MP. De-cowl, let it idle, spray ether, and find.
I would not fly this plane until I found the problem. You have not determined based on this data what the spread is at TO power and low altitudes. I would not attribute this to carb at all.
Breaking through 400 in a climb should not alarm you.
 
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Carb Jet

Steve,
I had the same thing going on when I was flying my 40 hour test period. I read everything I could find and finally did that test. I was POSITIVE I had no intake leaks. I finally drilled the jet out on the carb, which was a painless operation, and it took care of it. It even pretty much evened up the temps to peak.

For reference, mine is an O-320 also.
 
These are the richest MA4-SPA carbs, better than drilling out the jet.
10-5009N
10-5135
10-5217
 
You should be able to get a 150F or better EGT spread on all cylinders.
Induction leak is a good place to start. A can of ether is your friend.
Remember induction leaks are easily discernible at low MP. De-cowl, let it idle, spray ether, and find.
I would not fly this plane until I found the problem. You have not determined based on this data what the spread is at TO power and low altitudes. I would not attribute this to carb at all.
Breaking through 400 in a climb should not alarm you.

Thanks Kahuna. This test is now on my very short list.
 
Steve,
I had the same thing going on when I was flying my 40 hour test period. I read everything I could find and finally did that test. I was POSITIVE I had no intake leaks. I finally drilled the jet out on the carb, which was a painless operation, and it took care of it. It even pretty much evened up the temps to peak.

For reference, mine is an O-320 also.
Thanks Paul. Out of curiosity, did drilling up happen to also do anything to your CHTs or oil temp? These are what drove me to explore the gami lean and induction tests in the first place.
 
I'm not trying to be flippant, but how are these better than drilling the jet to a larger size?

Thoughtful engineers have carefully tailored the idle circuit, the accelerator pump, and main jet for optimum performance. A modified nozzle jet may cause the air/fuel ratio to be overly rich. There is a point of diminishing returns, where high-end fuel flows no longer increase but mid-range fuel/air ratios become too rich.

Sure, your high-end fuel flows begin to look better and so do your CHTs and EGTs. But unfortunately, mid-range fuel flows may become exceedingly rich.This rich condition is especially apparent as you transition between idle and full power and may cause problems on throttle application (like TO or GA).

There is no "approved" method to accomplish this procedure and if you mess it up you'll end up buying a new carb.
 
Walt is correct. There are several documents out there that detail exactly what he is talking about and the effects it can have written by the folks that designed these things.

That being said, I did drill mine but was careful to sneak up on it and not go too far. A reamer is the best thing to use if you are going to do it....

I found that the typical 10-3878 is too lean for a typical O-360 in an RV7.
 
These are the richest MA4-SPA carbs, better than drilling out the jet.
10-5009N
10-5135
10-5217
Thanks for your input, Walt. I liked the idea of just being able to swap something out. I went to the hangar to check and, unfortunately, it is a 10-5217 already. Any other options for getting more fuel (if indeed that were to turn out to be the issue)? Thanks again.
 
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Steve, mine was also a -5217. Like Brantel, I snuck up on the jet size. I had the most trouble with temps on full power at sea level. In cruise I didn't have much of a problem. As instructed by not only my engine builder, but many others on this and the yahoo groups, including Mahlon, I gathered the parts and drilled the jet out one step at a time till I got closer the fuel flow required for an O-320 at full power at sea level. I still bump 400 in a prolonged climb at 90 knots, so I just don't do that.

Before drilling, I couldn't get a rise in EGT of 100 degrees from full rich. Now it's closer to 175.
 
Im not a carb guy. Can someone explain how carb jet changes fix an inadequate spread on 2 cyl when the other 2 are just fine?
 
It doesn't.

In the process of tracking down some high temps, I did a GAMI lean test through Mike Busch's Savvy Analysis Program. The lean range for my four cylinders are:
1-205F
2-222F
3-68F
4-62F
Test is conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.

I am not sure what you did, but this is NOT what a GAMI lean test does. You do a GAMI lean test to find out what the spread in fuel flow is from the first to peak and the least to peak. Absolute EGT has nothing to do with it, nor what the difference in EGT is.

If I were to guess that test result had a big spread in fuel flow too and she was rough, but that may not be so.

You possibly have some induction leaks, you may need to use some carb heat to get better F/A ratio's or even partially close the throttle. You may just have an engine that won't play nice LOP. But most carby engines will if they are set up right.

As for over 400 CHT, best to avoid that if you can. And in the climb if you are seeing an EGT higher than say 1320, you may have a leak, or maybe just poor F/A ratios, so again maybe carb heat in the climb. But ONLY after you are sure you have no leaks or problems. No point masking defects.
 
Kahuna,
I maybe didn't understand the problem to begin with. I thought the OP was stating that he couldn't get the his engine to 150 degrees or so ROP. That was my problem and drilling the jet did, in fact, take care of that problem. I could only lean about 75 degrees from full rich to peak at 5000' DA and that was just not enough fuel even at full rich, at sea level.

From reading numerous threads, it's a very common occurrence it seems, especially with the O-320's.
 
Steve, mine was also a -5217. Like Brantel, I snuck up on the jet size. I had the most trouble with temps on full power at sea level. In cruise I didn't have much of a problem. As instructed by not only my engine builder, but many others on this and the yahoo groups, including Mahlon, I gathered the parts and drilled the jet out one step at a time till I got closer the fuel flow required for an O-320 at full power at sea level. I still bump 400 in a prolonged climb at 90 knots, so I just don't do that.

Before drilling, I couldn't get a rise in EGT of 100 degrees from full rich. Now it's closer to 175.

Same here ... We are now drilled to #40 - 2 sizes larger that it came.
 
I am not sure what you did, but this is NOT what a GAMI lean test does. You do a GAMI lean test to find out what the spread in fuel flow is from the first to peak and the least to peak. Absolute EGT has nothing to do with it, nor what the difference in EGT is.
Perhaps I mis-stated slightly. In doing the GAMI lean test, the difference in lean ranges is one of the indications Mike Busch wants to see. The other is the spread in the fuel flows from first to last to peak. Same test, two different pieces of information from that single test. See this article under "Diagnostic Tests" for elaboration: http://www.avweb.com/news/savvyaviator/191197-1.html FWIW, my spread was 1.7 gph. Obviously a bit hard to get LOP on all cylinders with this spread.
 
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Not sure what Mike is looking for by your explanation, and as I assumed above the fuel flow spread was large, 1.7GPH, and on an O-320 that is more significant than on a 300HP 540/550.

What you do when doing a GAMI lean is do one at say 6500' and then drop down to 2500' and do it by setting the same RPM and MP, and compare the results of which order they peak in, thus picking leaks.

There are other methods on the ground for the brave.
 
Kahuna,
I maybe didn't understand the problem to begin with. I thought the OP was stating that he couldn't get the his engine to 150 degrees or so ROP. That was my problem and drilling the jet did, in fact, take care of that problem. I could only lean about 75 degrees from full rich to peak at 5000' DA and that was just not enough fuel even at full rich, at sea level.

From reading numerous threads, it's a very common occurrence it seems, especially with the O-320's.
No, you are very correct, Paul. That was my primary concern on this initial post. The other factors, like higher than preferred CHT's are a secondary concern that may or may not be related. Thanks again for sharing your experience. If it comes to drilling up, I'll be happy to have had your input. Hopefully it won't come to that. Still working on getting a couple brave souls (myself included) to do an induction test on the ground.
 
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There are other methods on the ground for the brave.
Thanks David. If you're speaking of induction leak tests, I think I know what you mean about needing to be brave.

It does sound like maybe you and Mike Busch use some different terms for certain tests and/or he may offer a variation in how to run the tests. I also did what he describes as an "Induction Leak Test" in and according to the above article (http://www.avweb.com/news/savvyaviator/191197-1.html). In it one uses a high manifold pressure run and low manifold pressure run at the same altitude and then compares EGT differences at those different manifold pressures. I again found very significant differences b/w 1&2 and 3&4 which, according to the article and Mike's analysis company, is pretty consistent with induction leaks.

From High MP (23.75") to Low MP (18.75) at 5000MSL:
#1 dropped 123F
#2 dropped 153F
#3 increased 59F
#4 dropped (but only) 15F
 
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Induction leak is a good place to start. A can of ether is your friend.
Remember induction leaks are easily discernible at low MP. De-cowl, let it idle, spray ether, and find.

Just did the induction test today. Had a pilot friend idle it at about 850 rpm while I sprayed plenty of WD40 around the #3 and #4 induction tubes (where they meet the cylinder and where they meet the sump on both sides of the rubber hose). However, there was no noticeable rpm rise (to either myself doing the spraying behind the spinning prop or to the pilot in the cockpit).

Did I do the test incorrectly or is it just an indication that induction leaks are probably not my problem? Should I have seen an immediate and noticeable rise if I in fact did have a leak? This is the impression I got from the few threads I could find about how to do this test.

Thanks for everyone's help... still plugging away at finding what's responsible for my issues.
 
Umm, did the WD40 mess up your engine? Or did you mean something else. Your spray can should have said "starting fluid". AKA ether.
 
Umm, did the WD40 mess up your engine? Or did you mean something else. Your spray can should have said "starting fluid". AKA ether.
Thanks for the reply. Yes. I meant WD40. An old Alaska bush pilot/A&P said WD40 would be fine (and less flammable than ether) as have a few posts here on VAF. Still, since I was actually hoping to find a leak, I'd be happy to do it again if ether or starting fluid really would work better.
 
Thanks for the reply. Yes. I meant WD40. An old Alaska bush pilot/A&P said WD40 would be fine (and less flammable than ether) as have a few posts here on VAF. Still, since I was actually hoping to find a leak, I'd be happy to do it again if ether or starting fluid really would work better.

There are so few locations for leaks, just tape each one off with electrical tape....... soooo much safer.
 
I'm still stuck on, how to perform a GAMI FUEL INJECTION TEST
On a carborated engine. ; )

You can do the test, but you can't change the injectors :)

But you can work with carby heat and throttle plate position to get the best result you can.

You can also use it to find if you have intake leaks.

Works best with a CSU as the RPM staying steady makes for better stability of EGT and thus diagnostics.
 
My engine came from the factory with very loose primer fittings in the heads. Worth checking if you have them.
 
My engine came from the factory with very loose primer fittings in the heads. Worth checking if you have them.
I pulled my primer system for the summer at least, so I doubt it's that but will check all solid plugs in ports. Another idea... #3 has the MP fitting on one port... Should check that. Any problem with just removing my MP fitting for a flight or two? It's connected to my D180.

Thanks.
 
Use your engine monitor, safer and more diagnostic.
Can you recommend and describe such a test using the EMS that will to help me isolate whether my 2 lean cylinders are the result of induction leaks (which i so far cannot locate) as opposed to poor mixture distribution from the carb? From the professionals who have analyzed my data, those seem to be the two most likely culprits, but which it is remains anyone's guess. Thanks.
 
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Just did the induction test today. Had a pilot friend idle it at about 850 rpm while I sprayed plenty of WD40 around the #3 and #4 induction tubes (where they meet the cylinder and where they meet the sump on both sides of the rubber hose). However, there was no noticeable rpm rise (to either myself doing the spraying behind the spinning prop or to the pilot in the cockpit).

Did I do the test incorrectly or is it just an indication that induction leaks are probably not my problem? Should I have seen an immediate and noticeable rise if I in fact did have a leak? This is the impression I got from the few threads I could find about how to do this test.

Thanks for everyone's help... still plugging away at finding what's responsible for my issues.

Steve,
I just did a very non-scientific, dangerous do not do this at home, lighter flame test and the accelerant is WD-40 is barely flammable and only for a short period as compared to ether. No idea if they have changed these over the years. My can is probably 20 years old or more.
Carb cleaner, starting fluid etc. Get 2 cans and empty them out on your engine. Then report back!
 
Steve,
I just did a very non-scientific, dangerous do not do this at home, lighter flame test and the accelerant is WD-40 is barely flammable and only for a short period as compared to ether. No idea if they have changed these over the years. My can is probably 20 years old or more.
Carb cleaner, starting fluid etc. Get 2 cans and empty them out on your engine. Then report back!
Thanks Kahuna. Will do it again with something ether based. Will it really take that much or should I get immediate results with just misting the joints a bit? I had assumed the latter.

Will also do David's GAMI lean test sheet test above if I can figure out which one he is talking about

Many thanks again-all the help is appreciated on this frustrating issue.
 
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Thanks Kahuna. Will do it again with something ether based. Will it really take that much or should I get immediate results with just misting the joints a bit? I had assumed the latter.

Will also do David's GAMI lean test sheet test above if I can figure out which one he is talking about

Many thanks again-all the help is appreciated on this frustrating issue.

This is not frustrating. Just troubleshooting. You might find it in one squirt, you might have to empty a can all over the engine to find it. And if you empty one, you will wish you had 2. Intake leaks are common enough that you should have a spare can around for finding it. Now go and find that leak(s)!
 
Just to update. After using most of a can of starting fluid I still failed to find an induction leak. Nonetheless, I pulled the induction tubes on #3 and #4 to look things over along with my A&P friend. At his suggestion, replaced the gaskets as the original ones were super thin and didn't compress much at all. In addition, smeared a very light film of permatex on gaskets before installing. Went out and test flew and it seems to have made some difference. Flew again at 6000 ft, starting at about 65% power and leaned from full rich until EGT peaked on each cylinder. As with the first test, ran it a couple times and averaged the numbers.

Original Test from July 10, delta EGT (copied from original post) on:
#1=205F
#2=202F
#3=68F
#4=62F
fuel flow spread (from first to last to peak)=1.8 gph

Today's Test, delta EGT on :
#1=157F
#2=178F
#3=81F
#4=77F
fuel flow spread = 0.96 gph

In addition, CHT's on my two hot cylinders (#3 and #4) seem have come down about 8-10F and my oil temp dropped about 8-10F as well. (OAT similar on both days.) Will have to confirm temp drops with more tests.

This all seems to suggest that my mixture distribution is a bit improved, though it's still far enough off that I'd like to get #3 and #4 both running richer and and cooler. Next step? I suppose I'll have to call Aerosport and see if they have any ideas. As far as I know, the only thing I haven't done as suggested here is drill the carb jet up.
 
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Evening Mixture

Steve,
There was a thread a while back about a gentlemen who had put a honeycomb like plate between the carb and the sump in an effort to make his mixture more even. I couldn't find it with a quick search but it was very interesting to me and held, what I believe to be, a good fix. I've been watching for more results but haven't seen any.

If I can find the thread, I'll ask for an update. I think it's promising for us lowly carb guys...;)
 
Golly, one might think that something else is wrong with the early lean limit. Is there anything else that these two cylinders have in common, a coil . . maybe. Not saying that is it, but there is more than mixture that could be different for these two cylinders. And how long has this been occurring? I assume other mechanical considerations have data gathered too?

Sorry to ask questions, rather than give answers, but sometimes there are unvoiced assumptions or data that could help the bigger picture (or it would have be solved already).

Oh - ether scares me so I use a propane torch with no flame to pinpoint a vacuum leak, but may not work with a whirling prop so close. It also works to evaluate A/F ratio at idle, As usual, YMMV.
 
Steve,
There was a thread a while back about a gentlemen who had put a honeycomb like plate between the carb and the sump in an effort to make his mixture more even. I couldn't find it with a quick search but it was very interesting to me and held, what I believe to be, a good fix. I've been watching for more results but haven't seen any.

If I can find the thread, I'll ask for an update. I think it's promising for us lowly carb guys...;)
Thanks Paul. I think I saw that thread too but don't remember seeing any definitive results posted.
 
Golly, one might think that something else is wrong with the early lean limit. Is there anything else that these two cylinders have in common, a coil . . maybe. Not saying that is it, but there is more than mixture that could be different for these two cylinders. And how long has this been occurring? I assume other mechanical considerations have data gathered too?

Thanks Bill. I first did the lean range tests a couple months ago just after getting out of Phase 1 and having just read about it in Mike Busch's Sport Aviation article, though I think the poor distribution has probably been there all along. Not sure if #3 and#4 have anything else in common, but maybe Aerosport Power will have some ideas. If anyone knows what other data might be useful to have, I probably have it in my Dynon download files.

Sorry to ask questions, rather than give answers, but sometimes there are unvoiced assumptions or data that could help the bigger picture (or it would have be solved already).
All good!

Thanks again. What I'm really concerned about at this point is whether or not I should be flying the plane. While I'm OK once at altitude and flying at reduced power (like I was during during the lean range tests), I'm a bit concerned that at full takeoff power and lower altitude those back two cylinders are probably almost in that range just rich of peak where they are not really supposed to be. Anyone have any thoughts on this?
 
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You have not determined based on this data what the spread is at TO power and low altitudes.
Kahuna-I'm coming back to this first post you made because I think it may address my concerns about being especially way too lean at low altitude/high power situations. You are correct that all previous tests have been run at about 6000 MSL and at 65%. In terms of the test you suggest, are you thinking this is a 1000 AGL test run at full power or do you mean some sort of static test on the ground? Thanks.
 
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WOT?

Hay Steve,

It looks like you?re not doing your testing at WOT/wide open throttle, if you are then it?s not going to be an induction leak, if your testing at part throttle then it could be the throttle plate angle giving you poor distribution, try it at WOT and report back. At this point though regardless of distribution I would say your overall mixture is on the skinny side, however that may change at WOT.
 
Hay Steve,

It looks like you’re not doing your testing at WOT/wide open throttle, if you are then it’s not going to be an induction leak, if your testing at part throttle then it could be the throttle plate angle giving you poor distribution, try it at WOT and report back. At this point though regardless of distribution I would say your overall mixture is on the skinny side, however that may change at WOT.
Thanks for the input, Ross. I was just following Mike Busch's article as best I understood it, to do it at about 6000 ft and 60-65% power. Are you saying to go to whatever altitude it takes to get 60-65% at WOT and then do the test, or are you saying something different?

Second, I'm not sure I follow the clause highlighted in red. Can you clarify what you mean when you refer to WOT and induction leaks? I'm pretty dense on these kinds of issues. Thanks for the education.
 
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Thanks for the input, Ross. I was just following Mike Busch's article as best I understood it, to do it at about 6000 ft and 60-65% power. Are you saying to go to whatever altitude it takes to get 60-65% at WOT and then do the test, or are you saying something different?

Second, I'm not sure I follow the clause highlighted in red. Can you clarify what you mean when you refer to WOT and induction leaks? I'm pretty dense on these kinds of issues. Thanks for the education.
I would watch the EGT at takeoff and climb at WOT to get an idea of where they stabilize but I would not lean, yes then go up to 7000? and run your test at WOT to determine what your EGT spread is and your total mixture strength is, I would like to see a total of 200F ROP at full rich and WOT, if it?s less then 200F I would drill the jet.

Keep in mind that your mixture strength will probably/possibly get weaker/leaner as the throttle is reduced from WOT, doing the test at WOT will give you the fattest mixture your carb can give and it will give you the best distribution, the distribution might still suck because it?s a carb, there notorious for this, playing with the carb heat valve or even the throttle position can help fine tune the distribution on some engines.

At WOT induction leaks are not a factor because there is no vacuum in the induction system to pull air through leaking gaskets, with the throttle closed at idle there is high vacuum in the system and this is where your induction leak will show up the best.
 
I would watch the EGT at takeoff and climb at WOT to get an idea of where they stabilize but I would not lean, yes then go up to 7000’ and run your test at WOT to determine what your EGT spread is and your total mixture strength is, I would like to see a total of 200F ROP at full rich and WOT, if it’s less then 200F I would drill the jet.

Keep in mind that your mixture strength will probably/possibly get weaker/leaner as the throttle is reduced from WOT, doing the test at WOT will give you the fattest mixture your carb can give and it will give you the best distribution, the distribution might still suck because it’s a carb, there notorious for this, playing with the carb heat valve or even the throttle position can help fine tune the distribution on some engines.

At WOT induction leaks are not a factor because there is no vacuum in the induction system to pull air through leaking gaskets, with the throttle closed at idle there is high vacuum in the system and this is where your induction leak will show up the best.

Thanks for clarifying it, Russ. That makes sense. Just a couple more questions if you don't mind:
By 7000' I assume you mean 7000' density altitude?
What do you mean by "mixture strength" as opposed to EGT spread?

I really appreciate your help.
 
Your carb also has a power enrichment valve that close to enrich the mixture at near full throttle setting. It,s a mechanical link so it's always there.
 
Thanks for clarifying it, Russ. That makes sense. Just a couple more questions if you don't mind:
By 7000' I assume you mean 7000' density altitude?
What do you mean by "mixture strength" as opposed to EGT spread?

I really appreciate your help.

Yes 7000?DA but it doesn?t matter a whole lot, 75 % power WOT is fine so whatever altitude it takes to achieve that will work.

Mixture strength is a reference to fuel to air ratio, the stronger the mixture strength the richer the mixture =more fuel, we are measuring this using EGT. If your running 75% WOT full rich then begin to lean you would like to see an average of 200F before reaching peak EGT, two cylinders might be 250F and two might be 150F, the average would be 200 and I would not worry about it. Remember that Lycoming says at 75% and below you can run at peak so the test you ran at 65% showed you are safe however you don?t want to be that close at full power but you can?t safely test it at full power, that?s why I am recommending you test it at WOT but at altitude.

The problem you end up with even if you determine your fine and do nothing is that with a large unbalance in mixture strength between cylinders is that you can?t lean near as far as you might like before the engine goes ruff = poor fuel economy relative to an engine with a better balance, you can play with the throttle setting and the carb heat valve some to reach a better balance, you?ll just have to try it and see what you can get.
 
Thanks Russ! Your explanation really helps.

Because I have a really busy month at work and vacation (and jury duty) in August I won't be flying much but will report back when I have more results. FWIW, it seems that a lot of issues are coming together right now, one of which is I really need to have my prop repitched by Craig Catto b/c I can't run WOT straight and level at any altitude without overspeeding due to being very underpitched. Given my vacation/work schedule for the next month, and the fact that I need a properly pitched prop to do these next WOT flight tests, I'm going to go ahead and send my prop in next week. Just haven't wanted to be without a flying plane long enough to have it done before now.

Over the past year of flying I've come to realize that while there is a lot of documentation for what to test for in Phase I airframe wise, there is very little, and certainly nothing comprehensive, about what types of engine tests should be run during Phase I. I would think there would be a market out there for someone to fill book or magazine article(s) wise. I'm a bit embarrassed to be a year into flight and still chasing these things down!:eek:

Anyway, again I appreciate Russ's and everyone else's input.
 
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