SBC runs rough at highway speed
I have a mildly rodded SBC 400 in my truck. Edelbrock 600 CFM carb, Performer RPM intake, MSD 6al, HEI Vacuum Advance Dist. (stock coil), .202 heads and a mild cam (sorry I don't kno\w the grind, but it pulls a decent vacuum at idle).
It runs great at around-town speeds, and even better when I stand on it. It shudders and pops (jeez I hope it isn't detonation) at around 55 (3100 RPM). I can mash it and accelerate out of it. I tried openeing the choke a little when this occurs, but it didn't seem to help, so I thought it may be a rich problem. I went 2 stages leaner in the cruise circuit by changing the metering rods, which helped a little. It only shudders a little bit at 55, but starts to pop around 65 (3700 RPM) now. Could I have been wrong and I should be going in the rich direction?
I haven't ruled out a timing issue, but it behaves so well at acceleration and under 50 MPH, I just don't know. It also only has this problem under load. I can rev it progressively from 3000-4500 in neutral witrh no problems. I think the last time I checked it, I had 10 deg initial and 36 total at 2800 RPM. I need to get my advance light bqack from a deadbeat.
Anyone else have a similar problem, where you are a king at getting groceries or at the drags, but you can't do more than 50 on the way to a show? Thanks in advance, Chris.