I have a late 73 240z, and the engine sometimes surges. It is majorly underpowered, and seems like its only running on about half the cylinders. We replaced the fuel pump, had the points checked, replaced the air filter, and replaced the spark plugs and spark plug wires. The engine ran great for about 2 months. It started surging, so we checked and readjusted the valves (cold), and it ran perfect for about 2 weeks. I didn't run the engine over the weekend, and now have the same problem happening, the engine surges, and most of the time is severly underpowered. I have balanced the carbs. Should i try to readjust the valves hot? What should I do?

I have a question, what do you mean by surgeing ? Describe what the engine does . Is the engine still equipped with flat top carbs ? Are you using the stock ignition ? I doubt it has anything to do with the valves being out of adjustment. Make sure all electrical connections are tight including the engine ground strap , and are making good contact. Gary

Yes, I have flat top carbs. What the engine does it when I first start it up, it pulls reall strong, then it seems as if it cuts out. Some times when I apply light throttle, it will cut back in. But most of the time it is underpowered. It seems like only half the cylinders are working. Sometimes the engine all of a sudden "kicks in", and throws me back.

Stock ignition and stock distributor. Only thing new are wires and split fire plugs.

I would start by losing the SplitFires and replacing them with the proprer NGK's (JMO)

Yes after you dump the split plugs , and by all means do so , Do the same with the flat top carbs and get a set of SUs. For plugs just use NGK BPR6ES they are about $10.00 for the set. When you can afford it look for a ZX ignition , one with a 12 80 module on the side of the distributer. It's the little black box. All the dist. from '79 to '82 will work but the only ones that have the correct module are form the '79 & '80. Get the coil too , and be sure to get the mount that attaches to the block and the bottom of the ZX dist. your 240 part wont work. With these three things you will be amaised how much better the engine will run.