1977 T140v Runs Rough

How long have you had the bike? Was it running fine before?
It could be a number of things. Is the fuel fresh? If not drain and put fresh some E5 in the tank.
Sticking choke/cable. Fuel blockage. Air lock. Blocked carb jets. Dirty air filter. Damp HT caps/ leads. Flooding. Just a few of the simple things first.

 

Agree with Dave above, could be any of those but as it starts ok I'd o for the carb's pilot circuit first. Look here:

https://www.thetriumphforum.com/threads/t140v-amal-carbs-mk1.31915/#post-579003

 

hey whenever these have a bad idle, suspect a blocked idle circuit.

take the carbs off. remove the air mixture screw. inside is a metered orifice that controls the fuel delivery into the mixibg chamber under the venturi.

get a #78 drill bit--no larger. eBay has em in packets for cheap or go to a machinist supply house.

the bits are short. mix some epoxy and glue a bit into the end of one of those red plastic tubes that come with aerosol cans of brake cleaner or similar.

gently insert the bit into the hole under the idle air mixture screw and twirl it so it pulls the mung out do this several times to clear that hole the drill bit actually removes the deposits, while just poking in a wire or a guitar string forces the dirt into the mixing chamber.

spray carb cleaner into the air intake holes in the fron of the bell mouth. one of them leads to the mixing chamber and if all is well you will see cleaner squirting out of both holes in the floor of the venturi, back where the rear edge of the slide fits.

when that is clear, put the idle air muxture screw back in, all the way lightly to the bottom, then back out 1-1/2 turns. put the carb bac.

do this to the other carb.

it may not be the cause of your problem, but this is so common and so easy to correct that there is no point in doing anything else until youre sure the idle circuit is okay