Sounds like it is leaned out a little. Have you tried backing out the idle mixture screws a bit? I like to start by gently turning the mixture screws in all the way counting the number of turns. Both sides should be equal. I generally find 1 1/2 turns out is a good starting point, but some engines will like 1/2 turn out while others want 3 turns out. Just as a test, I'd start it cold and as it warms up, I'd back out both mixture screws 1/2 turn extra to see if it runs better once warmed up. If so, try playing with them more.
If you do rebuild, I believe the Carter carbs have a model number stamped on the baseplate, possibly facing the radiator. Ideally, you can order a kit to match this model number and you're good. If not, what I generally do is disassemble the carb and compare the old gaskets to the new set I'm buying. A lot of sellers on eBay take good exploded views of their kits allowing you to ensure you're ordering the right set.
