Translation:I cannot bring a suitcase when taking a taxibike.
Well "Ojek" isn't a word anyone would use in English. "Taxibike" isn't a word I'd ever heard before in Australia, but it may have been used in the past, or in other English speaking areas like Hong Kong or India. Most English speakers will certainly be able to figure out what "Taxibike" means without any trouble.
I got answers from native speakers. https://hinative.com/questions/18421929
The original Indonesian sentence is grammatically INCORRECT, but the expression is widely used in daily conversations. Inserting "ketika" (formal) makes the sentence grammatically correct, but it is a bad collocation for "aku" (informal). Here are alternative solutions:
"Saya tidak bisa membawa koper ketika (or saat) naik ojek." -- Note: "naik" is a verb and cannot function as a preposition or a conjunction.
"Aku tidak bisa bawa koper pas koper naik ojek. -- Note: "pas" is for informal. One native speaker argues "waktu" is informal, but another says it is formal. So, I guess "waktu" is between "ketika/saat" and "pas".
"Aku gak bisa bawa koperku di ojek." -- Note: "gak" is more informal. "Di" as a preposition means "on a taxibike" whereas "pas naik" does "when riding/taking a taxibike".
Hope this helps!