The WiModem, marketed by Jim Drew at his CBMSTUFF company, has incompatibilities with the Commodore 128. Verified on Atariage and on Lemon 64, there seem to be 2-3 problems. Arnuphis at Atariage writes,
"In 128 mode it interferes with the disk drive mode. Fine in 64 mode though. It works with the Reloaded Mk2 but causes a lot of screen jitter due to issues..."
TomXP411 on Lemon64 writes,
"...the user manual explains that the UP9600 mod breaks Burst Mode."
"...I found online how to solve for it by cutting pin 5. Works fine now at 2400. (I never used 9600 anyway)."
This should probably be posted on the CBM Stuff forum so he can be made aware of the issue and hopefully fix it. I have only used it with my C64 and it has been fantastic. I was planning on trying it out with the 128 but maybe not.