'68 Chrysler 318 / 210 HP Unusual Misfire

We just got a '68 Barracuda with the 210 HP Chrysler 318 with some problems which have me stumped. It misfires badly below 2,000 rpms, starts to smooth out above that, misfires some around 3,000, but runs just great above that, including wide open (4,600 with 12x15 cup)! I put all new tune up parts on it (plugs, points, condenser, rotor, cap) and the misfire is actually a little worse now, but the topend rpms are higher! I'm having the Carter AFB rebuilt now because it needs it (its leaky), but I don't think that's going to solve the problem.

The engine has decals on the exhaust manifolds with tuning specs including valve lash adjustment recommendations. Does this engine have solid lifters that need to be adjusted periodically? If so, could that cause a strange problem like this?

Also, the engine doesn't warm up like it should even in 60 degree water and air, so I spent $ on a new 145 degree thermostat, but that didn't change anything. The temp gauge looks like it goes to maybe 90 degrees and my infrared temp gun indicates that the front of the cyl heads after an hour of running are only about 110 degrees. The water circulation hoses seem to be in the correct places for this engine.

I will appreciate any advice or insight on these problems.      

Hi,

Thanks for your reply. We haven't checked the timing yet. I was very careful with the plug wires, but I rechecked them with the Chrysler engine manual we have with my sons looking on. I didn't think it was the wires because the engine runs and sounds so good above 3,000 rpms. My tuneup seems to have made it run even rougher than before in the lower rpms, but much better (perfect) above 3,000. I'm still not certain about whether this engine has solid lifters that need adjusting and if that could cause a problem like this. Still, just my tuneup affected it as described above with no changes to timing or lifters.

Larry,
When you opened up the distributor, did you take a look at the mechanical advance? They can rust up and need some oiling. You may also have a broken spring?