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XP-400 Still Coughing

Chris Engler

Active Member
I posted last week after a first start regarding some issues with a CS WW prop not moving and the XP-400 coughing /stumbling at high RPM. Happy to say the prop issue is resolved but the engine stumble is still a mystery. The engine is new and the fuel system is the standard Silver Hawk EX-5VA1. The ignition system is standard mags with the G3i system.

The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.

All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.

At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.

The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.

I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.

Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....

Thanks!
 
Any other data you can post? 150 ROP should not be rich enough to cause coughing/sputtering; It is pretty much what you are looking for. Symptoms you describe are classic for overly rich, but your testing seems to show you are not.

Did you confirm the EGT movement on all 4 cylinders? It is possible that you have a problem with one of your nozzles allowing too much fuel into one cylinder. You should confirm the EGT status for each cylinder if you haven't done so already, ensuring that you track the trend for each.

Also, what condition are you seeing 18-19 GPH? Is that at 2600 full rich or peak EGT. I don't know the chart for a 400, but it seems a bit high for 2600 RPM, especially if at peak.

Larry
 
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I posted last week after a first start regarding some issues with a CS WW prop not moving and the XP-400 coughing /stumbling at high RPM. Happy to say the prop issue is resolved but the engine stumble is still a mystery. The engine is new and the fuel system is the standard Silver Hawk EX-5VA1. The ignition system is standard mags with the G3i system.

The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.

All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.

At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.

The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.

I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.

Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....

Thanks!
Interesting. I'm having similar symptoms. New Silverhawk system on IO-360. Please reply back with the findings on your FI system from the evaluation.
 
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Larry - the 18-19 gph figure is at 2400 RPM full rich. I've confirmed that the EGT's are consistent across all cylinders and as you say, the 150 degree increase to peak at 2400 is just about right. Funny thing is the engine runs flawlessly everywhere except above 2400 RPM full rich...really has us stumped!

Bryan - interesting that you're having similar issues.....yours runs fine everywhere except top end and can lean to overcome the coughing?

I'll keep you posted on what Precision says....hope to hear back from them by end of next week.

If the throttle servo gets a clean bill of health, next step is to replace the mags but really seems like a fuel mixture issue.
 
Larry - the 18-19 gph figure is at 2400 RPM full rich. I've confirmed that the EGT's are consistent across all cylinders and as you say, the 150 degree increase to peak at 2400 is just about right. Funny thing is the engine runs flawlessly everywhere except above 2400 RPM full rich...really has us stumped!

Bryan - interesting that you're having similar issues.....yours runs fine everywhere except top end and can lean to overcome the coughing?

I'll keep you posted on what Precision says....hope to hear back from them by end of next week.

If the throttle servo gets a clean bill of health, next step is to replace the mags but really seems like a fuel mixture issue.
No, I've not tried leaning at full power. But I will.
 
Any chance you have a fuel leak somewhere, perhaps at some fitting, causing cavitation?
With mine, no. Pressure and flows, steady. No fuel smell inside the plane. Same conditions, right or left tank. Something in the servo? Possibly.
 
No sign of a fuel leak with mine either and with it not coughing when I lean, indications are that it's stumbling rich. The A&P I'm working with noted puffs of black smoke from the exhaust during the stumble....another indication it's rich.
 
Thanks Mahlon....we had thought about that possibility as well but figured it would be similar to a full throttle static run-up of a fixed pitch prop (i.e., solid running at a static RPM of 2300-2400) rather than inducing a cough. If I keep my throttle at full without leaning, my engine will actually quit. I tried putting cowls on and doing a couple of high speed taxi runs and had the same result...once throttle fully advanced, heavy coughing.
 
Crazy thought: Valve timing, due to cam gear installed one tooth "off"? Is that even possible? :confused:
 
Crazy thought: Valve timing, due to cam gear installed one tooth "off"? Is that even possible? :confused:

I briefly thought the same, but it just doesn't add up. Incorrect valve timing would have more consistent issues that would be hard to detect (at one tooth off) and should not impact mixture, only power delivered.

Larry
 
Try checking the low pitch blade angle on the prop...maybe too steep.
Good Luck,
Mahlon
Mine only stubbles when it has reached full operating temp. Not below.

Thanks for all the ideas/suggestions! Chris, hope you don't mind me piggybacking your post...
 
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The 18-19 GPH figure sounds very high to me. My O360-A4M, fixed pitch, has never seen anything above 15.5 in flight.

When you pull the mixture back to keep it running above 2400 RPM, what is the fuel flow? I suspect it is somewhere in the 14-16 GPH range.

EDIT: Sending the fuel servo back is the right approach, IMO. Hopefully you sent the divider too.
 
Pete and Larry...thinking more along the lines of fuel/air since I can prevent coughing by leaning and get 2600 RPM in a static run-up leaned but appreciate the thoughts.
 
Bob - I pulled the fuel servo, spider, and injectors and sent them off to Precision for bench testing this week...nothing was loose as it was disassembled...hope to hear back from Precision late next week.
 
Not enough air?

Could your intake be blocked or not flowing enough air? Filter issue? Something reducing airflow would affect air/fuel ratios at high RPMs.
 
I saw something very similar to this on a Champ with a bad exhaust muffler (a plate came loose and partially blocked the exhaust at high power).

Carl
 
The 18-19 GPH figure sounds very high to me. My O360-A4M, fixed pitch, has never seen anything above 15.5 in flight.

When you pull the mixture back to keep it running above 2400 RPM, what is the fuel flow? I suspect it is somewhere in the 14-16 GPH range.

EDIT: Sending the fuel servo back is the right approach, IMO. Hopefully you sent the divider too.

+1

I looked yesterday and my 320 was drinking 11 GPH at 2400 under high load (climb). Your 400 is about 25% larger in displacement, which would equate to a bit less than 14 GPH at 2400. 18 seems filthy rich at that RPM and not surprising it is coughing. I hope they find the issue in the servo.

Larry
 
Thanks to all who have offered suggestions....your collective brain power is much appreciated!

My thoughts as I continue to chase the coughing:

- Fuel flow does seem high at 18-19 gpm. Using the IO-390 charts and adjusting for field elevation of 800 feet ASL, I should be seeing around 15 gpm at 2400 RPM fully rich. Keep in mind everything is new and un-calibrated including the red cube which is using the GRT standard default programming value of 83.

- Fuel pressure....appears to be a gauge/programming issue. We've confirmed the mechanical pump is a high pressure version and the electric pump delivers almost 60 gph to the throttle servo so it doesn't appear to be a fuel delivery problem.

- Restriction in air flow....I'm using the stock Vans snorkel and AN air filter but also ran with cowl off and alternate air open so plenty of air available. My understanding is that the fuel servo uses the air tubes in the front of the inlet to the servo to meter the correct amount of fuel to the injectors. If that's correct, an undersized snorkel would simply result in not reaching peak power but not cause a stumble since the servo would meter based on air available and would not overly richen the mixture.

- Exhaust restriction....this is a very real possibility....going to remove and closely inspect. The link below is a post that sounds very familiar and the root cause was a blocked exhaust.

https://www.pilotsofamerica.com/community/threads/engine-issue-o-360.53888/
 
Update on the exhaust inspection....nothing out of order, pipes clear and baffles looked fine using a borescope. Spoke to Clint at Vetterman's and he kindly offer to ship a set of straight pipes to try. If the fuel servo gets a clean bill of health from Precision, going to try a new set of mags and the straight pipes...the saga continues!
 
Update on the exhaust inspection....nothing out of order, pipes clear and baffles looked fine using a borescope. Spoke to Clint at Vetterman's and he kindly offer to ship a set of straight pipes to try. If the fuel servo gets a clean bill of health from Precision, going to try a new set of mags and the straight pipes...the saga continues!

I don't think an exhaust problem would cause excess richness. You would see a limited ability to increase power, but would not see coughing/sputtering and belching black smoke. That is pretty typical of an overly rich mixture and exhaust restrictions simply restict total flow. mixture is set by the carb or servo and metered by total air flow. I don't see how an exhaust restriction can cause a rich mixture in a mechanically metered (i.e. air flow based) setup, as they are designed to match fuel to the current air flow present.

I suspect they will find something in your servo.

Larry
 
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Update

Wanted to post an update on the XP-400 situation. As I mentioned in previous posts, I noted an engine cough/stumble during a first start on an RV-8 project. The engine will run perfectly up to around 2500 RPM. At that point, with mixture full rich, advancing the throttle will result in a noticeable power loss with RPM to dropping into the 2200-2300 range while the engine coughs and some backfiring occurs. The strange thing is if I lean the engine approximately 1/3 of full travel, (i.e., 1/3 of the way back from full rich) everything is fine and I can reach and hold 2600 RPM which is the max static RPM I should reach per the MT governor manual. Over the past few weeks, I've tried the following to isolate the problem....all made no difference at all:

1. Installed new mags provided by Superior

2. Had the fuel servo bench tested/calibrated at the factory (Silver Hawk EX-5VA1). Per the factory, the servo was spot on in terms of flow volume and required no adjustments to the calibration.

3. Removed the snorkel and performed a test run.

4. Tried a different fuel servo provided by Superior.

5. Removed the mufflers and bore scoped them to verify no obstructions.

6. Replaced the mufflers with straight pipes.

At 2500 RPM and full rich (i.e., just before the trouble starts) the engine parameters are as expected....EGT spread highest to lowest is around 50 degrees, fuel pressure is 30-31 psi, manifold pressure is steady at 26-27 inches, and fuel flow is around 18 gph.


At this point I'm out if ideas other than pull the motor and ship it to Superior....any other thoughts from the collective wisdom of VAF is welcome and appreciated!
 
One Of First Checks

For me would be valve springs and/or lifters after you've extensively exhausted all other possibilities that you've addressed.
A weak lifter, broken or weak valve spring causing a 'float' issue will display the same symptoms. Cross contamination of either exhaust or intake cycles will make the engine behave as you've described.
Just a thought. Something to investigate and hope it helps.
 
It seems apparent that the servo is throwing too much fuel at your engine in the higher RPMs. The fact that you are seeing clear signs of an over rich mixture (sputtering / belching black smoke) and pulling the mixture back allows the engine to produce full power (or close to it) would indicate that the engine is healthy and you have a fuel metering issue. A reach, but have you confirmed that you have the servo model appropriate for your engine size? Also, I would pull an injector and get the part number. Have the folks at silverhawk confirm it is the correct part for your engine/configuration. I am not a servo expert, but would have concerns that too large of an injector nozzle might allow too much fuel to flow. I can't remember if the servo meters just flow or also factors in pressure. The servo is expecting several pounds of pressure in the injector lines at that flow rate and too large of an injector would reduce that pressure and allow more fuel flow than the servo is counting on.

Can we assume this ran on some firms test stand or dyno for an hour or two? That should eliminate a lot of variables in the engine, as you have a theoretical confirmation that it is capable of properly producing the power it should.

It's too bad they banned Don from this forum, as I am sure he would have some good input.

Larry
 
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Thanks for the suggestions. Valve float had occurred to me as well but since I can lean and get a solid 2600 RPM, I still tend to think it's a fuel delivery problem as Larry suggested.

Larry - from my discussions with Precision Airmotive (the fuel servo manufacturer) the servo meters the amout of fuel throughout the RPM range via four air inlet tubes in the throat of the servo based on "velocity pressure" acting on a diaphragm valve to meter the correct amount of fuel. What's perplexing is that the metering process is working across the entire RPM range and then something is breaking down over the last 100 RPM. Per the Precision web page (and confirmed through discussions with them) injectors are consistent (i.e., same part number) from the 320s through the 540s so it's unlikely there's a mismatch on the injectors but certainly worth pulling and checking all 8. The other problem with the injector theory is that if the servo is doing its job correctly metering the amount of fuel for a given air volume through the servo throat, it would seem that even injectors that are too large would only have the appropriate amount of fuel volume to inject into the cylinder based on airflow though the atomization my be off.

Also, forgot to mention previously, I've confirmed the plugs are in fact the same plugs listed on the engine build sheet and they're black in color when pulled and inspected suggesting an overly rich mixture as opposed to grey suggesting overly lean.

Regarding the history of the engine before I purchased, it's serial number 004 of the XP-400 run. The first 5 engines were the "test mules" used in program development. My engine log shows 150 hours of bench running between 2007 and 2008 with various combinations of accessories, then in 2008 a teardown for internal inspection (no wear or issues noted) and was subsequently reassembled with new rings, bearings, and gaskets and preserved. Another 5 hours of run time was documented in November 2011 and the engine was again preserved. I purchased the engine in 2013 from Superior during the initial phase of the RV8 build.

On a brighter note, I'm getting a valuable education in the operation of fuel injected airplane engines as a result of all this!
 
Chris, I had an engine with the same symptoms your having and was told by two IA's and the engine shop that assembling an engine with the cam to crank timing being off was impossible. There are dots on the gears that line up and it's a no brainer.

However, after weeks of research and inspecting myself I found this to be the problem.

Have YOU verified that the cam to crank timing is correct? I posted a link on the last page but now I cannot get it to work for some reason.

Bring #1 cylinder to TDC. Pull the rocker cover on #2. both valves should be closed. Moving in either direction of #1 TDC opens opposite valves on #2

If the cam to crank timing is off one of the valves on #2 will be slightly open which is incorrect.
 
The other problem with the injector theory is that if the servo is doing its job correctly metering the amount of fuel for a given air volume through the servo throat, it would seem that even injectors that are too large would only have the appropriate amount of fuel volume to inject into the cylinder based on airflow though the atomization my be off.

This was my understanding as well, but had no real detailed backup to support it. Just throwing out oddball possibilities at this point, due to odd nature of your problem. There has to be a reason your servo is pushing too much fuel.

Best of luck resolving this.

Larry
 
I have not personally checked but will definitely look into it. I mentioned it to my A&P a couple of weeks ago and he indicated the cams are indexed with a keyway so not possible to misalign but sounds like you've heard the same thing and turned out not to be the case. The other point made by the mechanic is that since we can get to 2600 by leaning, it can't be an internal timing issue which does sound reasonable. The other thing he mentioned is that a cam timing issue would show up across the RPM range, not just at the top.

For your situation, did the problem present just at the higher RPM or across the board?

The link you posted worked for me when you first posted a few weeks ago but I can't get it to work now either...I'll see if I can track it down and will repost if I can find it.

The strange thing to me is that my problem is absolutely repeatable (right at 2500 RPM every time) and it feels like a "system wide" issue (i.e., uniform EGTs and just a reduction in RPM with coughing). I does not appear to be a single component issue like an injector or mag.
 
I have not personally checked but will definitely look into it. I mentioned it to my A&P a couple of weeks ago and he indicated the cams are indexed with a keyway so not possible to misalign but sounds like you've heard the same thing and turned out not to be the case. The other point made by the mechanic is that since we can get to 2600 by leaning, it can't be an internal timing issue which does sound reasonable. The other thing he mentioned is that a cam timing issue would show up across the RPM range, not just at the top.

For your situation, did the problem present just at the higher RPM or across the board?

The A&P's are wrong. You absolutely can have incorrect cam timing. It is true that the gears are keyed to cam and crank. However the actual cam timing is set by aligning the proper teeth on the crank gear, idler gear and cam gear during assembly (by aligning dots on specific teeth on those gears). They could easily be installed one tooth off. The A&P's should be saying that it is not possible if the installer is paying attention to what he is doing. The engine was assembled by a human and, as we have learned, the species is capable of errors and mistakes. However, being a full tooth out of time is a lot and don't see how you wouldn't notice the problem across the RPM range.

All of that said, cam timing would show problems across the RPM range. Further, cam timing does not impact mixture. The only way to have black plugs and belch black smoke is to have too rich of fuel / air mixture.

Larry
 
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The other point made by the mechanic is that since we can get to 2600 by leaning, it can't be an internal timing issue which does sound reasonable. The other thing he mentioned is that a cam timing issue would show up across the RPM range, not just at the top.

For your situation, did the problem present just at the higher RPM or across the board?

The link you posted worked for me when you first posted a few weeks ago but I can't get it to work now either...I'll see if I can track it down and will repost if I can find it.

The strange thing to me is that my problem is absolutely repeatable (right at 2500 RPM every time) and it feels like a "system wide" issue (i.e., uniform EGTs and just a reduction in RPM with coughing). I does not appear to be a single component issue like an injector or mag.

So on my engine with a fixed pitch prop at full rich I could get to 2100RPM and then it would fall on its face belching smoke and coughing if I kept advancing the throttle. If I leaned it out it would clear up and run to about 2300RPM.

On mine what really tipped me off was on two cylinders the plugs were tan and the other two had black sooty plugs.

All of that said, cam timing would show problems across the RPM range. Further, cam timing does not impact mixture. The only way to have black plugs and belch black smoke is to have too rich of fuel / air mixture.

Larry
Larry just in simple terms think about this. The more pressure in the cylinder the more gas it needs to be happy. On my engine that was a tooth off the engine would start ok, run fine up to a certain point and idle smooth. The problem came when I asked it to make a higher HP than it was capable of doing.

When the cam timing is off the intake OR exhaust valve on two or maybe all the cylinders is opening at the wrong time reducing the cylinder pressure which would in turn lower the required fuel to the cylinder causing an excessively rich mixture and leaning the engine will increase the HP.
 
So on my engine with a fixed pitch prop at full rich I could get to 2100RPM and then it would fall on its face belching smoke and coughing if I kept advancing the throttle. If I leaned it out it would clear up and run to about 2300RPM.

On mine what really tipped me off was on two cylinders the plugs were tan and the other two had black sooty plugs.


Larry just in simple terms think about this. The more pressure in the cylinder the more gas it needs to be happy. On my engine that was a tooth off the engine would start ok, run fine up to a certain point and idle smooth. The problem came when I asked it to make a higher HP than it was capable of doing.

When the cam timing is off the intake OR exhaust valve on two or maybe all the cylinders is opening at the wrong time reducing the cylinder pressure which would in turn lower the required fuel to the cylinder causing an excessively rich mixture and leaning the engine will increase the HP.

I still struggle to understand how cam timing can make the engine run rich and belch black smoke. That said, I have never improperly timed a cam and have no real experience with the results in an fuel injected engine (I still believe it is not possible with a carb). Clearly you do and I agree that OP should take heed and check for improper cam timing. It's hard to ignore real world data/experience. The similarity in symptoms and the inability to find an issue with the metering device makes this a good path to follow.

After thinking some more, it may make sense. If the cam is timed early, it could be causing flow pulses in the intake. The cylinders would still be moving up when the intake opens and exhaust closes (normally exhaust closes after TDC) and that would put pressure into the plenum instead of the normal vacuum, and get worse as RPMs went up. I don't know the servo well enough to know how it would deal with that. In the end, the servo isn't mixing the fuel with the air, it is just sending fuel based upon what it thinks the airflow is. If it is getting tricked into thinking more air is flowing through it than it really is, too much fuel will be delivered to the injector and you get a rich condition.

To the OP: if you pull the left mag, you should have a decent view of the crank and idler gear interface, though you may need a mirror and penlight. I am unsure if you will be able to see the cam /idler gear interface though (may require two mirrors or dental camera) A lycoming manual will show you the proper configuration of dots on the gears. Don't forget the cam turns at half the speed. You'll need to be at TDC on #1, if I recall. But you'll also need to be in the proper cam phase (compression/power vs Exhaust/intake). As birddog mentioned, you should be able to see if your off a tooth by having an experienced engine guy observe the in/ex valve position and behavior when at TDC on the int/exh stroke. This is normallly done by measuring the Degrees from TDC when the intake valve begins to open, but I don't believe lycoming publishes the intake opening details. However, a full tooth is a lot and you should be able to see that the in/ex overlap is occuring too far before (early timing) or after (late timing) TDC.


Larry
 
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Larry and Birddog - thanks so much for tanking the time and sharing your experience on this. I'm heading out tonight for some business travel but will forward this info to my A&P and have him check for the "one tooth off" condition you're describing. I'll post results as soon as I have an answer on this possibility.
 
Chris,

Jumping in here late in the thread I realize, but is this a new engine from Superior or was it built by a third party? I have been considering a Superior XP-360 for my bird but two reported instances of issues on brand new engines does cause me some concern about their final testing process. Up until this thread they seemed to have had good feedback. Or at least no bad feedback. Please clarify the builder.

Thanks.

Ray
 
I Think We're on to Something....

Following up on the information provided by Birddog and Larry yesterday, I stopped by the airport yesterday evening and ran through the procedure Birddog described. My conclusion was there was a problem with cam alignment. Having minimal experience with Lycoming type engines, I called the A&P I'm working with and asked him to confirm. He called this morning to confirm he feels the cam alignment is "one tooth off". I want to stress these are preliminary findings but based on the misaligned rocker geometry on Cylinder 2 while at TDC on cylinder 1 and the fact that we've ruled out everything we can possibly think of, I believe we've found the problem.

When I return home later this week, I'll begin the process of engine removal and getting it prepped for transport/rework.

Ray - regarding your question on the engine builder, mine was purchased from and built by Superior at their facility in Texas. That said, it has a bit of an unusual history in that it was one of the first five engines and they were used as "test mules" for the XP-400 program (see my post on the engine history from 10/14). As such, it was actually assembled twice by Superior - once for the original build and then following a 150 hour test run period, a second time following disassembly to check wear, tolerances, and replace bearings and rings. Following the second build, the engine log provided by Superior indicates it was run an additional 5 hours in the test cell. I spoke with Superior this afternoon and at least preliminarily, documentation at their shop of the 5 hours of run time following the ring/bearing replacement (i.e., second build) is not readily available but they will continue to search.

I don't want to say anything that could be construed as negative about Superior or my experience with them until pulling the accessory case off the motor (which will necessitate pulling the motor off the airplane) but will report the facts of what we find when I feel 100% certain about what's causing the problem so others that experience similar problems in the future have information that may be helpful.
 
Wow! This was and is an interesting thread, and right now, I feel like it's the last "Walking Dead" show of the season...and I can't wait to find out what happens next...
 
Following up on the information provided by Birddog and Larry yesterday, I stopped by the airport yesterday evening and ran through the procedure Birddog described. My conclusion was there was a problem with cam alignment.

When I return home later this week, I'll begin the process of engine removal and getting it prepped for transport/rework.

I spoke with Superior this afternoon and at least preliminarily, documentation at their shop of the 5 hours of run time following the ring/bearing replacement (i.e., second build) is not readily available but they will continue to search.

Chris, good to see you are going to send it back. Lets say your measurements are perfect -the cam is off. It does not explain the symptoms. If, however, there are torsional problems due to, say a loose crank gear, then the static cam timing could be off and going absolutely crazy as the rpm increases affecting both ignition and cam events. Please post the final answers when concluded. Hope they check the crank for issues as well.
 
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Anyone mentioned bad valve spring yet? This happened on an O-300 they spent lots and lots of money fighting a similar issue intermittent stumbling at full power usually after just getting good and warmed up on departure climb. After lots of wasted hours and money they took all the valve springs off and measured them and they did not meet spec.
 
Bill - I'm not an expert by any means when it comes to the inner working of aircraft engines but Birddog experienced the same symptoms I'm having and it turned out his cam gear was a tooth off. From my from discussions with Superior yesterday, they indicated they've seen a cam gear a tooth off and the engine started fine and ran fine until the top of the RPM range when it simply wouldn't reach expected RPM and wouldn't make full power (though no coughing/stumbling in their case). They didn't indicate if their motor was carbed or fuel injected. Perhaps the fuel injected motors will cough rich in this condition and the carbed motors don't ? The symptoms coupled with the incorrect rocker geometry on cylinder 2 at TDC indicates that the cam is off a tooth on my motor. Weather that's the only problem remains to be seen but my engine is very predictable in terms of symptoms and exactly what RPM they present so I'm guessing once we have the cam alignment set correctly all will be well. The engine will be sent to either Superior themselves or one of their authorized shops for a thorough evaluation/repair followed by time in a test cell at all ranges of operation.

BNT83 - thanks for the tip on the valve springs - definitely add that to the list of things for the shop to confirm!

More details to follow....
 
Root Cause Identified!

http://tinypic.com/usermedia.php?uo=NuVqmzAy/KzBCg7ce4KwNoh4l5k2TGxc#.We1Ja2hSyM8

As it turns out, the problem is the result of incorrect cam to crank timing! For those not familiar with the cam to crank alignment, the photo above shows the cam gear on top aligned with the idler gear (note the "0" with a "dot" on either side). The crankshaft gear is the one on the bottom in the photo. Note that the "0" on both the idler gear and crank gear should align. On my engine, it's clear that the crank is misaligned relative to the cam by one tooth. As a result, the valves are not in the correct position relative to crank (and piston) positions.
 
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http://tinypic.com/usermedia.php?uo=NuVqmzAy/KzBCg7ce4KwNoh4l5k2TGxc#.We1Ja2hSyM8

As it turns out, the problem is the result of incorrect cam to crank timing! For those not familiar with the cam to crank alignment, the photo above shows the cam gear on top aligned with the idler gear (note the "0" with a "dot" on either side). The crankshaft gear is the one on the bottom in the photo. Note that the "0" on both the idler gear and crank gear should align. On my engine, it's clear that the crank is misaligned relative to the cam by one tooth. As a result, the valves are not in the correct position relative to crank (and piston) positions.
 
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