My 1990 honda civc won't go over 3000 rpm... it has a 1.6 D.Over.Head.Cam.. I hope there's someone that might no what's wrong with it

I'd begin by going over the electrical system. Consider replacing the spark plugs (NGK only), rotor, distributor cap, and spark plug wires. Most importantly, test/replace the Ignition Control Module (ICM) and coil. AutoZone can test these two components for free. Here's how to replace the ICM and coil:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-4.html#post265896