Low RPM harms for carbureted car?

With ford pinto engine, my car user manual says, don't drive your car with low rpm.
And there's most efficency area on RPM gauge from 2500 to 4000. Like we all see in bus or trucks.
max. Torque @4000 rpm

so if my car EFI, i can say high gear low rpm brings economy but with carburetor i can't say anything.

should i use my car around 2500rpm in urban?
any experience with ford pinto weber carby engine?

Hi the issue is around american engineering actually unlike us brits your cars are not built with any precision when it comes to machined parts. We have instances where this has been proved.
like a rebore her on a camaro engine we found bore out an engine because the difference between the piston and cylinder would be a difference of some 30 thousands of an inch over and above the size of the piston. This being bored out to + 40 thousands of an inch the piston would be new and a difference of less than 5 thousand of an inch 0.005 so when fitted with piston rings it would be extremely tight. The result meant that the engine would take and extreme amount of power required to turn it over.
so it would not be what you would call a running fit.
however in recent years we have found that many engines now are built with a lot more tolerance between the pistons and cylinder bores so it is a running fit. So fine when injection systems are used for fuel. However the old style Carb cars did not like running at slow engine speed due to so much slop in the components in the engine
so that is why your car does not run at low revolutions it is just to wide on it's tolerances between the pistons and cylinder walls. To much movement will not keep it running fast enough as gas escapes down the sides of the pistons.

It's nothing to do with engineering precision, nor whether the engine is carbureted or injected. It is a simple fact that it is not good for an engine to be forced to run too slowly or too fast for long. The best region is around mid rev range, which is most efficient and least wearing. In other words, don't make the engine "lug" or rev its nuts off.

Read bottom of the first page about, how to drive it to achieve 30 mpg,
http://www.caranddriver.com/comparisons/chevrolet-vega-vs-ford-pinto-archived-comparison
the two people I knew that owned. Them drove them normally.

Absolutely nothing to do with engineering tolerances.
There's no difference in the way you would drive a carburetor equipped car or a fuel injected car.
The fact is any engine will have an ideal speed at which it produces the most torque.
The diesel comparison is different as the characteristics of a diesel is to produce maximum power and torque at a much lower RPM.

Long term operation at low RPM allows buildup of carbon in engine and exhaust system.

Invite a friend to a weekend trip to a place about 100 miles away.
Tell them you will supply the car and they must supply their meals and spending money.
Drive the car at 55 - 60 mph during the trip as that should burn out any carbon deposits.

VANNA? Can I buy a verb?
Pintos were not EFI, so you built it, what were you thinkin?

Your "car user manual" would not necessarily apply to your own creation.

Find out what you are using really and then compare fuel economy estimates, or run some laps and measure I think is best advice.

As long as you are not lugging your engine, you will not damage it. The lower the RPMs within reason, the better the fuel economy will be.

Just forget everything you read and forget tachometers. The big idea for least engine wear and best mileage is a smooth sound and smooth motion. Sound and motion are sensed by your ears. That was true for your grandpas and its still true for you… And everyone else driving any car.

As long as you are not lugging your engine, you will not damage it. The lower the RPMs within reason, the better the fuel economy will be.