How do your plugs look?
None of us can feel how your bike pulls at low speed over the internet. We rely on data you provide about your bike. Each engine has a horsepower and torque curve. The shape of this curve determines where you feel power from the bike in terms of acceleration. Take a look at the curves here:
http://www.totalmotorcycle.com/school-SectionSixB.htmThese are curves there for A DOHC CB750. But, the SOHC 4 should be similar.
Short of a dyno that measures horsepower/torque at any given RPM, the home mechanic is limited to time/distance and total weight moved measurements during the event. With this data you can make charts for your bike and determine specificaly if something need adjusting. Reading the spark plugs can also help dial in for the best carburation adjustments.
Your carburetors have an idle mixture screw that has a very limited range of effectiveness and also only effects very small and low increments of throttle position. You've seen the idle screw end taper and the orifice it fits into. It's pretty small. And, the slow jet that feeds it is even smaller. The I.M.S. ceases to have much restrictive control when it is turn out quite far. Opening up the slow jets should have wider throttle range effect in the band you seem to be concerned about.
Something else to consider is how you think about your carbs and engine performance. The RPM you are turning effects the total airflow demand on the carb. The slide position allots what is to be provided. A CV carb controls the slide opening based on engine demand. Your slides are mechanically linked to your throttle grip and that position is important to note for whatever speed you wish out of the engine.
Put differently, while the fuel metering devices in the carb do respond to pressure demands of the engine (RPM), the slide exerts direct control over the Main and needle jet fuel flow, but, NOT the slow jet or idle mixture screw.
I mostly ride a CB550, also an inline four. It does not make the horsepower and torque of a CB750. But, the shape of its horspower and torque curve should be similar to the 750 of the same vintage.
I consider its low speed pickup to be good. But, if I want to really scoot I do so in the lower gears as high RPM is where it makes it's best horsepower. For example, if I'm cruising at 50MPH and want to quickly pass a car, I'll drop two maybe even three gears if I'm riding two up. I'll want, at least, 4000 RPM to achieve best acceleration. But then, my red line is 9300. And, I'm not shy about using anything and everything below that limit and sometimes beyond. With the clutch disengaged, it will wind to red line from idle in less than a second or, "right now" for all practical driving purposes. If I want a high power band, I select a gear the puts the engine in that band.
If you want a bike that responds to throttle without regard for transmission gear selection, you'll probably be happier with a V twin like the Harley configuration. It's Horsepower and torque curves are pretty flat from low RPM and throttle positions. Gear selection is less critical for these bikes.
Cheers,
