rough mid-range and carb questions

I was starting to think I'd have to switch from heat gun to torch.  A nice welding glove helps. 

I was able to sneak in a couple runs before the storms got here, and I'd say moving the needle from 3rd to 4th made it worse.  It almost won't run just above idle now, and the plugs were just black as soot.  I changed plugs to the original set that were pretty clean.  After that, I did another run mostly around 3500-4000.  The plugs I had just put in were also sooty black.  I know this isn't the best plug color test, but I'm wondering if I went the wrong way on the needle.  Since I've perfected the technique of moving the needles, I'll drop them to the 2nd slot, then give it one more try before pulling the carbs for overhaul.

I can officially blame Trond for making me buy a dual AFR unit.  https://www.innovatemotorsports.com/dlg-1-dual-lambda-afr-gauge-kit.html    I probably won't install it permanently due to limited space, but I'll set it up temporarily for some ground runs to see what the AFR is.    

Rusty

looking forward to how it responds to 2. slot !  And what a nice AFR gauge... Should be enough to test on ground I would think

Sadly, slot 2 was no fix.  It did seem to run smoother up to about 3000 RPM, but 3500 was still as rough as ever.  I do suspect it's too lean though, because I tried an ignition check at 4000, which seemed rough on both, and was really rough on either ignition alone.  I didn't even bother to note the RPM drop because it was too rough to let it keep running there.  It's never done that before. 

I brought the carbs home for rebuild, and have already taken them apart.  I was really hoping to find something suspicious, but I haven't.  The o-rings look perfect, floats brackets aligned properly, float pairs 5.8 and 6.0 grams, no debris.  The only thing I haven't taken apart is the throttle shaft, and I have no reason to believe that wasn't done 4 years and 60 hrs ago.  What I can see of the o-ring looks perfect, and the screws are obviously non-factory peened.  I will probably go ahead and file those screws down and remove them, just to leave no doubts.  I'll toss everything in an ultrasonic cleaner tomorrow, then reassemble.  I plan to go ahead and build it to the ULS specs, (2.70 needle jet, and 155 main jets). 

From the looks of the carbs, I have a near zero hope that this will fix anything.  The only thing I expect to gain from it is a new 5 year countdown on the carb rebuild, and ruling out carb wear as my problem.

Rusty

then maybe not the carbs causing it...   other checks could be shut off fuel supply and see if engine runs better as it leans out. And pull choke to see if it likes more fuel

Agree with setting at stock. It should run with that but you are about there already. Did you say earlier that sockets and o-rings are good (and no vacuum leaks), measured compression or leakdown (even with new engine) and eliminated risk of ignition (two plug wires mixed up (if it runs nice anywhere on both circuits then not likely).  Are the vacuum slides moving freely and same from side to side ?  I had one that jammed once in the bore

I haven't tried shutting off the fuel, but I have tried the choke without any real success.  If it's a rough RPM, the choke might seem to smooth it out, but that's only because it speeds up to a higher RPM.  When the throttle is closed to bring it back to where it was it's still rough with the choke. 

The engine shaking was starting to tear the sockets, and they were recently replace along with o-rings.  One additional difference was that I added the drip trays ( https://www.leadingedgeairfoils.com/drip-tray.html ) when I put the engine back together.  I now see a note in the parts list that says- "Not suitable for direct installation of the air filter on the carburetor. Forseen for airboxes without drip tray".  Is there some way they could cause a problem, or is this just saying it's not a configuration that Rotax used?  I've been thinking of taking them off just in case.  

I did leakdown tests, and all cylinders are 78/80.  Since it idles, and runs well at high power, I didn't really suspect an issue, but it was easy to check.  

I've spent way more time on ignition than I probably should have.  There are times when this absolutely seems like an ignition problem, but other times it doesn't.  The engine runs well at idle, and high power, and I've done flight tests (over the airport) with each ignition separately.  The fact that it runs well at high power with each individual ignition tells me there's no chance any wires are crossed.  Along the way, plugs, plug boots, wires, coils have all been replaced, sometimes more than once.  Swapping ignition modules makes no change, and they're fairly new.  The one thing I haven't checked is the pickup gaps, though I made sure they were not loose, and I verified the proper resistance of the pickup coils.  I don't know if the gap width is something that would cause my issue, but it's definitely on the list to check after the carbs fail to solve the problem. 

The vacuum slides certainly appear to move freely, and there are no cable issue.  When I've done the carb sync (using CarbMate) I've verified that the balance stays pretty stable across the normal RPM range.  I did notice that the engine almost won't run with the balance tube disconnected until it's fully warm.  There are probably enough clues here that I should be able to figure this out.

Once I get it running again, I'll try to capture some vibration data with a phone app, and see if there is a specific frequency, or if it's just randomly misfiring. 

Thanks for all comments.

Rusty