I had the 904 rebuilt on this 71 Duster and reinstalled it. I also removed the engine and painted everything up while the transmission was out. Now that I have everything together, it's running pretty well but there is this rattle or half rattle half chipring type sound from under the hood.

One thing that I have verified is that it doesn't do it when the vehicle is in Park or Neutral. Only in gear. You hear it a little bit at idle and then as you start accelerating, it starts to get worse up until a certain point to where it either goes away or I can no longer hear it due to the engine noise.

If I sit in the driveway and hold the brake down and push the gas in a bit, you can really hear it. I used a stethoscope and probed around and couldn't pinpoint it with that at all. It kind of sounds like it's coming form the carburetor to me (carter bbd).

Anyone have any ideas? It 100% doesn't make the noise at all in Park or Neutral.

I would check carefully for an exhaust pipe or hanger rubbing on the body/frame or other close approach point. This can change when you put it in gear and the motor/trans mounts flex.

Lou

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Home of Slant6-powered fun machines since 1988

Exhaust leak? I have what I thought was a ping/knock but now suspect is an exhaust leak from the manifold gasket. It's only noticeable when the engine is under load.

Thanks I'll check the hangers and make sure everything is clear there.

Rich, the possibility for the exhaust leak is there because I have the manifold with the crappy choke pocket design but why would it only happen under load? I can't think of why it would matter if it was under load or not if it was the exhaust.