Typical issue but EGT is not a magic number
EGT is relevant to each other and frankly Lycoming does not give a MAX EGT.
If able try to switch probes, but before you do that (since things look OK to me), you need to check for being to LEAN which you already sound like you suspect.
The acid test:
climb to 8,000-8,500 feet density altitude (approx)
WOT - side open throttle
mixture full rich
note all EGT's and start to lean very slowly and pause
note EGT rise
note the cylinder "first to peak" and note that peak EGT temp
(The test is done, but you can keep leaning and see the 2nd, 3rd and last to peak or lean till rough.)
Take the FTP "first to peak" and calculate the difference or delta between FULL RICH and PEAK EGT. About 150F min difference at 75% power, rich EGT to peak EGT. You might get away with a little less than 150F, but 80-100F is too little. The solution that works time and time again is to remove the main jet and drill it out one or two or three drill #'s larger. Usually worse case is three # sizes larger but you may only need one or two # sizes larger. Some guys can't lean at all with out getting immediate EGT drop.
Note: As you probably know don't lean at or above 75% power, which is max power to safely lean. That is why you go to +8,000 feet WOT. You can try to just throttle back and do this at a lower altitude and regulate power to 75%, but this is not ideal. We try and do standard test under the same conditions so we can compare apples and apples. With the throttle partially closed the butterfly will redirect the fuel more towards the front, since that's the way the butterfly is shooting the fuel into the plenum. Makes sense and YOUR aft EGT's are hotter?
If you are only getting 80-100 you need to do some magic jet drill. People resist this but its almost a certainty you need to do it and you will be glade you did. Your engine will run cooler and make a little more power. WASTE OF FUEL? Lets put it this way if you fly around and never get below 75% power and lean than yea you will use more fuel. At full power and a larger (drilled) jet fuel flow will be a little higher BUT YOU NEED HIGHER FUEL FLOW, again to keep temps down, avoid detonation under must critical conditions and make rated power.
The Carb manufacture DO not make a jet for RV's. The best Jet they have is just almost enough. Now we are taking EGT RICH to LEAN difference at 75% power WOT.
The Absolute number of EGT is NOT really important if all is well with the engine. Once you have established what is NORMAL EGT, yes, low or high EGT from the norm, can indicated mechanical issue. Go to the GEM web page. They have a cool user manual that gives you advanced engine troubleshooting and analysis using with EGT.
Bottom line is YOUR EGT's may be perfectly fine. What counts is difference between cylinders and difference between peak and rich at 75% power for each respective cylinder.
YOUR CHT's are OK below 400F but may be a little high. You did not mention the OAT and altitude. Lean mixture could be causing your CHT's to run a little hot for my taste.
You might need a little baffle tuning. Usually the GAP between the baffle and fins on #2 (fwd left) and #3 (aft right) are too small since the cylinder fins are shallow where the cylinder and baffle meet. The fact your #3 is hottest is normal; you may be able to get the temp down by increasing the GAP between the baffle and cylinder. The lower wrap around part of the baffle chokes the flow, especially on jugs #2 and #3. What is a little weird is your #1 (fwd right) is hotter than your #2 (fwd left). Usually #2 CHT is hotter than #1. Look at baffles again. Again #3 is expected to be hottest, which yours is, but #4 should be lower in my opinion. Again look at baffles. There could be probe issues?
CHT balance is pretty good, but you should try to be a little cooler. What are your climb CHT's? All could be a symptom of being a lean.
Guys do run around lean for years and get away with it, with out burning valves but some do burn valves. There are reason you can live with lean mixture, like Lycoming put in some margin to detonation and often we don't make full 100% power, especially with fixed props (low RPM on take off) and pilots do throttle back after take off. PLUGS! If your spark plugs look white or very light grey, you're lean.
However I don't see any thing really weird. The biggest thing is you look a little lean, and that is causing your CHT's in cruise to be a tad high. You did not give OAT. On a real hot day, high humidity (low density) it might be normal. Being lean with a CARB is normal with RV's and most need the jet drilled. Cheers. email me if you need help drilling.
