My $.02 says the "rattle" is lean out preignition or the resistance spring in the vac advance is weak. There's a deg. advance vs. in. vac. chart in the manual somewhere. I finally figured out that you had to check the function of the centrif advance vs. rpm with the vac disconnected and plugged, then check the vac advance on top of the centrif with a hand vac pump. What about accelerator pump functioning? Main fuel metering is done part fixed jet conventional, and part feedback controlled solenoid. At least two other circuits have feedback controlled solenoids, but I put that stuff out of my memory when I went to efi. I've got a working 87 carb I'd sell you subject to having it solve your problem. All you'd be out is freight both ways. Email me.