Hi, very nice to see you have some success on you first attempts, congratulations! Remember, this is an experimental ride, the engine could do well if properly constructed but many variables can make a difference. Your temps without the cone is looking not too bad, cone on makes a big difference. First your cone might be too restricting, check that.
There are a zillion difference things which might upset your egt, here a a few to start with:
- Clearance turbine wheel NGV too large (+0.15mm)
- Clearance compressor wheel, casing too large (+0,2mm)
- Fuel needles not touching burner stick walls
- Rotor not correctly balanced
- Bad bearings
- Combustion chamber not correctly constructed, needs to be consequent and tight on the front/rear cap, fuel tubes not closer than 8mm to front wall, 10mm ideal.
- Diffuser inaccurate built, all angles, clearances and openings are critical
Maybe as a simple test you can re position the egt probe or even stick it less far in in an attempt to jump the start, maybe you are measuring in a hotspot. The rpm region between 18.000 - 25.000 is critical and needs to be continued fast. After that it cools down and you might be able to do some furter tests. Can you actually see the exhaust bright red glowing during starting phase? Do you have some pictures?
Nice to hear about another GR130

! Please share some pictures with us.
Very best regards,
Gerald