mscom

That is Carranza's Ryan B-1 Brougham (M-SCOM, c/n 98), but not Carranza. Apparently that is a mechanic from Wright Aeronautical to check out the Wright J-5 Whirlwind radial engine on the aircraft.

When Ryan designed this range of comfortable monoplanes he named them Brougham. It was a name inherited from the British Lord Henry Peter Brougham who had designed and built a four-seat carriage for his own use in 1838. There had been other later vehicles also called Brougham which by then simply referred to something very comfortable to travel inside.

Carranza (Mexican Army) was sponsored by the largest daily newspaper in Mexico, the Excelsior, hence the ad on its side.

M-SCOM was a Brougham B-1, most likely c/n (MSN) 43 since that aircraft is missing from all production lists.
It was registered in May 1928 and flew San Diego-Mexico City on 24 May that year. Carranza then tried to set a record between Mexico City and Washington DC on 11 June but bad weather force him down at Mooresville, NC. He continued on the 13th (one source says 12th) but crashed at Mount Holly, New Jersey and was killed.
The photo above is most likely taken either when after his return to Mexico City on 24 May or when he departed again on 11 June.
Stig