stereo cartridge on mono record

The follow link shows how to to wire a stereo cart for mono playback, you might want to take a look at it.

http://pagesperso-orange.fr/jlf/erepro2.htm

A stereo cartridge is sensitive to vertical modulation of the groove. A mono record has only horizontal groove modulation, and whatever vertical movement occurs (and this includes turntable rumble) is pure noise, and you don't want it. It is essential to remove sensitivity to vertical modulation by jumpering the two channels together, or using the MONO switch on your preamp (if it has one).

Improved results may also come from using a different (larger) stylus, and these are available for some stereo cartridges.

you are fine fine fine

When Stereo records were introduced in 1958, we all had collections of mono LP records and played them one and all with the new stereo cartridges, whose needles were some 70% of the diameter of the old mono LP needles. We were always cautioned, however, that damage would result if stereo records were played with the old mono needles. Soon even mono record players came with stereo cartridges. Todays computer designed precision cut diamonds are far, far, better than anything we had back then, and dig out much more information, while being much gentler on the record groves. Despite theory, I generally prefer the sound without engaging the mono button.

Samujohn...It isn't "theory". Vertical groove modulation in a mono recording is pure noise. You are saying that you like some noise mixed in with your music.

Try this...
Connect one channel of your cartridge inverted.
Jumper the two channels using a Y interconnect or a MONO switch. (Now you have a cartridge that is insensitive to horizontal groove modulation and sensitive to vertical).
Listen to your mono LP. What you hear is what is mixed with the music when you use a stereo cartridge without a Mono jumper.