Hello,

I got the Dart running this weekend. I bought it with 74,000 miles from older couple, and they said they couldn't start it. Turns out the starter switch was stuck, easy fix. She started right up after 3 trys, with the ignition key turned on and a screwdriver on the starter. It idles great, but when I took it for a ride, above 2500 rpms (I think) it sounds like the valves are rattling. Didn't sound healthy. Is this common? What should I do?

It sounds like, in all those 74,000 miles, the valves where never adjusted. Its .010" for the intake valves, .020 for the exhaust valves. I do it while the engine is running, some like to do it with the engine off. Either way, its easy to do, the running methode just beats up your hands! Oh, don't forget that you have the intake valves side by side in the center (#3 and 4). Dont ask how I know...
Eric W

Is it a sharp, loud tapping that goes away if you accelerate or slow down above or below that 2500 RPM? My 1970 slant six Duster developed that noise, and it turned out to be the camshaft sprocket and timing chain. The sprocket (original equipment nylon over aluminum) had nearly stripped, I think it had about a half dozen teeth left on it when I pulled it out. Check yours ASAP.

Could this be spark knock? (Detonation) Do you have fresh gas in the car?
Does the noise get louder if you accelerate harder, does it go away when you let-off the gas??
DD

The car has been sitting for over a year now, could be old gas. I put in some dry gas a week ago to prep before driving. The noise starts around 2500 rpm (although I do not have a tach). The noise is loud enough that I am afraid to give it more gas, so I back off.

Yes, the noise goes away when I back off. It idles great and runs smooth up until around 2500 rpms. New plugs, oil, fuel filter.

I think that Doug got it right. It's probably detonation. Try filling it with high test and see if it guiets down. If it does it's detonation and might be caused by the old gas, carbon build-up or incorrect timing. When you here detonation back off. It does terrible things to your engine.
Bob D