1988 Honda Accord carburetor

When I start my car, the engine tends to run very high for the first 5 minutes in the winter and about 3 minutes in the summer until the engine warms up. I change the oil every 3k miles and has a little rust but still runs smoothly once the engine warms up. My mechanic says it is the carburetor which is dirty. He says even if he tries to clean it doesn't mean the engine still won't run high so it's not worth spending $1,000 to clean it. He says Honda doesn't have 22 yo carburetors in stock. He says the only thing I could do is to use the fuel cleaner each time I fuel up and the carb choke cleaner with the engine running. I use only high octane gas because if I use regular or anything else the car tends to have engine knock a lot. I run the air-condition which tends to lower the idle but still higher than normal. Is there anything else I can do? Or is there some other problem?