The WT-340 is a stock carb for ryobi's in trimmer form and it should have close to an 8mm venturi and it does have both high and low speed needles but they are typically covered with caps. If it's not drawing fuel the float needle could be stuck and the main needles and passages could be gunked-up. May want to completely disassemble the carb , soak it in cleaner, blow out all of the openings and reassemble it. Careful with the float so as not to bend the tang(changing the float level) when handling it.

I have used larger carbs with excellent results. If you can find a WT-324 or look for a WT-891 as they both have 11.1mm venturies and there are others out there as well but don't go too large on the venturi size.

If you want to use a remote pulse port you can drill and tap the case of the engine and install a fitting.