Motorcycle Repair: 1984 honda 200s, honda 200s, vent hose

Question
my 3 wheeler only starts somtimes and it wont stay running somtimes it does but after like 15 min it dies i clean the plugs and put new gas in it and it doesn't do anything  

Answer
Here's what I would do.

If there a vent hose in the gas tank cap? Check that it is working and not clogged or kinked.

Disconnect the fuel line and drain gas into an approved container from the petcock valve. Is it flowing freely?

Clean carbs and check them according to manual.

See: http://www.motocom.com/motorcycles/1984/1/1/294