Roland,
Sounds like you have been down every avenue. The engine you described sounds good. My assumption is that you also have a new capacitor as well as the new coil. Everything else makes it worst brings us to either spark or gasoline. I had an 8 cylinder that drove me nuts which had a new distributor cap that got a good deal of moisture in it due to a rather large puddle. Even after it along with everything else was dried out and after a close inspection, which turned up nothing wrong, the motor would misfire like it had bad wires. Like you.., I went down every path and finally changed the distributor cap because it was the only thing I hadn't replaced twice because it was new. Bingo the motor purred like a kitten. Apparently after closer inspection it appeared that it was arcing from the center point randomly to the plug points. Maybe the moisture or maybe a defective cap. To this day I always save my old working distributor cap as a spare, just in case.
If you try the carb and it doesn't help, I would try a new set of plug wires not bunched together in the wire holder and a new distributor cap just because.
One last quick question, anything unusually going on when this problem first showed itself. In my case it was rain.
On Second thought 9 psi at idle I think is low. Have you checked the intake manifold for cracks or loose bolts. Also the carb ? My flathead 6 cyl pulls 21 @ low idle and rock steady. I am not sure with my 29 I don't think I have had the need to check it. Probably should just for a point of reference.
PS... The reading I am using for vacuum is measured in inches of mercury.
21 inch of mercury = 10.31 psi So 9 psi at idle may not be a problem if you are measuring in psi.
Chet...
Sounds like you have been down every avenue. The engine you described sounds good. My assumption is that you also have a new capacitor as well as the new coil. Everything else makes it worst brings us to either spark or gasoline. I had an 8 cylinder that drove me nuts which had a new distributor cap that got a good deal of moisture in it due to a rather large puddle. Even after it along with everything else was dried out and after a close inspection, which turned up nothing wrong, the motor would misfire like it had bad wires. Like you.., I went down every path and finally changed the distributor cap because it was the only thing I hadn't replaced twice because it was new. Bingo the motor purred like a kitten. Apparently after closer inspection it appeared that it was arcing from the center point randomly to the plug points. Maybe the moisture or maybe a defective cap. To this day I always save my old working distributor cap as a spare, just in case.
If you try the carb and it doesn't help, I would try a new set of plug wires not bunched together in the wire holder and a new distributor cap just because.
One last quick question, anything unusually going on when this problem first showed itself. In my case it was rain.
On Second thought 9 psi at idle I think is low. Have you checked the intake manifold for cracks or loose bolts. Also the carb ? My flathead 6 cyl pulls 21 @ low idle and rock steady. I am not sure with my 29 I don't think I have had the need to check it. Probably should just for a point of reference.
PS... The reading I am using for vacuum is measured in inches of mercury.
21 inch of mercury = 10.31 psi So 9 psi at idle may not be a problem if you are measuring in psi.
Chet...