You get exactly what you pay for with those cheapo pods -- you might as well be running velocity stacks for how well they "filter" the air.
UNI makes decent pod filters too, out of the same foam that comes in every dirtbike airbox. But like I said earlier any set of pods requires a carb swap to work properly. These stock carburetors require a significant amount of vacuum to raise their slides and pods simply don't provide that. To make things worse, with pods, the amount of air flowing over them while you're rolling is widely different between the outer two cylinders and the inner two cylinders. The only way to vacuum balance them so they'll run right at speed is to intentionally imbalance them.
Here's a more detailed explanation for you. In your CB750K, the stock carburetors are referred to as CV or Constant Velocity carburetors. When you pull the throttle cable in the stock carb setup, you open up a butterfly valve in all four carbs to increase airflow, and the internals are carefully designed to use this to generate vacuum that pulls the slides up to increase air volume and fuel flow. These carburetors are therefore sensitive to intake system geometry and vacuum, and in the case of our stock carbs they do not want anything but the stock airbox.
The correct carburetors for pod filters or velocity stacks are called "direct-pull" carburetors. Instead of opening up a butterfly valve with your throttle cable, direct-pull carburetors have the throttle cable attached directly to the slide. You yank on the throttle, the carb opens up and lets in more air and that pulls more fuel. Much simpler design with no fancy internal vacuum passageways, and intake geometry/vacuum changes won't keep the carb from functioning.
You can get a set of four Mikuni round-slide direct-pull carburetors in a ready-made set for your bike from Cycle X, but you'll pay a good $1200+ for them. As far as I know that's the best carb setup you can buy for these bikes off the shelf and will make you the most power.
There's a dual-carb direct-pull setup sold by a company called Murray's that is also popular, but doesn't look as pretty in my opinion because it uses a big four-into-two aluminum intake manifold. That's about half the price of the Cycle X carbs.
It's a very good idea to get that stock airbox and all its boots back on the machine if you're sticking with the stock carbs. That way you, as a novice motorcycle mechanic, have a clear and obvious roadmap of how it's supposed to look and work in the form of the factory service manual and parts diagrams. When you're just starting out and don't know what you don't know, that's the best way to avoid making big mistakes.
UNI makes decent pod filters too, out of the same foam that comes in every dirtbike airbox. But like I said earlier any set of pods requires a carb swap to work properly. These stock carburetors require a significant amount of vacuum to raise their slides and pods simply don't provide that. To make things worse, with pods, the amount of air flowing over them while you're rolling is widely different between the outer two cylinders and the inner two cylinders. The only way to vacuum balance them so they'll run right at speed is to intentionally imbalance them.
Here's a more detailed explanation for you. In your CB750K, the stock carburetors are referred to as CV or Constant Velocity carburetors. When you pull the throttle cable in the stock carb setup, you open up a butterfly valve in all four carbs to increase airflow, and the internals are carefully designed to use this to generate vacuum that pulls the slides up to increase air volume and fuel flow. These carburetors are therefore sensitive to intake system geometry and vacuum, and in the case of our stock carbs they do not want anything but the stock airbox.
The correct carburetors for pod filters or velocity stacks are called "direct-pull" carburetors. Instead of opening up a butterfly valve with your throttle cable, direct-pull carburetors have the throttle cable attached directly to the slide. You yank on the throttle, the carb opens up and lets in more air and that pulls more fuel. Much simpler design with no fancy internal vacuum passageways, and intake geometry/vacuum changes won't keep the carb from functioning.
You can get a set of four Mikuni round-slide direct-pull carburetors in a ready-made set for your bike from Cycle X, but you'll pay a good $1200+ for them. As far as I know that's the best carb setup you can buy for these bikes off the shelf and will make you the most power.
There's a dual-carb direct-pull setup sold by a company called Murray's that is also popular, but doesn't look as pretty in my opinion because it uses a big four-into-two aluminum intake manifold. That's about half the price of the Cycle X carbs.
It's a very good idea to get that stock airbox and all its boots back on the machine if you're sticking with the stock carbs. That way you, as a novice motorcycle mechanic, have a clear and obvious roadmap of how it's supposed to look and work in the form of the factory service manual and parts diagrams. When you're just starting out and don't know what you don't know, that's the best way to avoid making big mistakes.