Your ignition timing may be changing as a result of the distributor moving or the points moving. Make sure that you have everything tight. Make sure you have the correct resistor wire from the coil to the points. If you used just a standard length of wire the points may be burning and changing the dwell angle and timing. The least likely problem could be a sheared pin on the distributor gear. I did have this on an Olds 455 that I was running in my boat There was just enough of a burr on the shaft to keep the gear from spinning freely. One more problem I have seen is a bad harmonic balancer. The rubber went bad and the outer shell of the balancer would move around. This caused the timing to appear to change. If this is the case you will not notice any change in dwell angle but the timing marks will move. You will also not notice any change in engine tone or drivability.
About your exhaust question - On the Left you can get the correct dual exhaust manifold (P/N 384893, casting code S) these can be found on all 1965 and 1966 Starfires and some 1965 to 1970 full size cars. You will also need to fabricate a shift link that goes from the frame to the trans if you do not have a floor shift. Or you can keep the single exhaust manifold on the left and have a custom pipe bent for the left side. You will need to do this anyway with the Toronado manifold. On the right side manifold you can just cap off the cross over port. This is what was done at the factory on B and C body cars with dual exhaust. I do not know of anyone that mass-produces headers for the 65 – 70 B and C body cars. You may have some luck having a set of custom headers made.
Some of the others on this site may have better ideas. Maybe we will hear from them?
__________________
1966 Ninety Eight Convertible - 425 Tri-Carb, Factory Dual Exh, Switch-Pitch THM400, 3.54 Posi.
1966 Catalina Wagon - 421 Tri-Power, M21, 4.11 Saf-T-Trac, 8 Bolt Wheels
1989 IROC-Z - 5.7TPI
|