Well I’m back with the same issue that has had me pulling my hair out for months now.
Everything I do seems to make it a little bit better but nothing I have done has completely eliminated the issue.
I didn’t want to create another post but I’m just lost and have no idea what’s causing it.
It’s a 300hp crate 360 Magnum, roughly 25-30k miles on engine.
Dualnplane M1 4bbl intake manifold.
Quick fuel super street series 680cfm vacuum secondary carb.
Firecore electronic vacuum advance distributor.
Crane cams hi-6 cd ignition with crane cams Ps92 e-core style coil.
Taylor thundervolt 8.2mm plug wires.
Ngk bkr5e spark plugs brand new indexed and gapped at .40.
Timing is 18 initial 32 total all in by 3400-3500 rpm.
Vacuum advance on manifold vacuum to add 12 degrees timing at idle for a total of 30 degrees at idle.
Issue is I have a rough spot around 2500 rpm and I have not been able to determine the cause.
First I though it was bad plugs and wires, so I replaced them, it helped a little bit didn’t eliminate it, next I tried a new coil, I did have a crane lx91 coil I bought a brand new crane ps92 coil didn’t notice a difference.
Then I thought it was rotor phasing, I’ve verified rotor phasing is correct on my current firecore distributor.
I have verified the timing mark on the balancer with a piston stop.
I’ve verified timing with two dial back lights bothnare within a 1/2 of a degree of each other.
Then I pulled the distributor and put stiffer advance springs inn to slow the advance rate down from all in at 2400 to all in at 3400.
That seemed to help but again did not eliminate the issue.
Then I pulled the plugs again to look at them and seen that cylinder number 8’s plug was semi fouled, not totally but it was darker then the other 7 and a slight smell of fuel to it.
So tonight I am doing a compression test on cylinder 8 with engine warm to see if there is an issue there.
If compression checks out then i don’t know where to go next.
Maybe the crane ignition box? That’s the only piece I haven’t tried swapping out.
But I’d like to confirm it is the issue before spending money on another ignition box and going through the trouble of wiring a new box inn.
I have a steady 20hg of vacuum at idle with vacuum gauge.
I did a compression test about 7-8k miles ago and all 8 cylinder cranked out 150 psi even across the board with carb wide open and engine warm.