Lots of 454 Issues...
I am having some major problems with the 454 in my 64 Chevelle. A little background, I bought the car as a half done project, and thought the engine was actually solid and good to go. Everything else had to be done to the car, but I thought I was free of engine work. Also, I bought the car from a guys wife (she got it in a divorce) so I really don't know much about the engine, except that it is a 454, possibly bored out, with a more aggressive cam than stock (no idea what it is), Holley 650 DP, Edelbrock dual plane intake manifold, and headers. I have done some research on it by the casting numbers and it looks to have come out of a 72 era Corvette. It took a while for me to get it running, but I have gotten it to run and drive, and it seems to drive pretty smooth, but there always seemed to be a huge lack in power. With what I know about this motor, it should be blowing the doors off this car.
Here's a list of what I have done to the engine:
-Rebuilt the carb
-Adjusted the valves
-Installed a new MSD ignition system
-New Accel 8.5mm wires
-Multiple sets of new plugs
-Installed a AEM Air/Fuel Ratio gauge to help with tuning the carb
-Increased the carb jet size based on the initial A/F gauge reading
Here's a list of the issues I am having with it:
-Vacuum is all over the place. I have hooked up a gauge to multiple manifold vacuum ports and the needle is bouncing all over the place. When I say bouncing, I mean bouncing, between 2-12" Hg. It seems to smooth out a little, and go out to 15" Hg when I rev it up, but at idle it isn't even readable.
-Multiple dead cylinders. The idle is pretty rough at cold startup, I thought it might just be the cam, but the other day I used my infrared thermometer and read the temp on the header tubes while it was running. Most were reading pretty close (cant exactly remember the value, but around 270-290 I think), but then a few of them were around 130, much lower than the others. I then pulled the plug wires while it was running on #1, nothing happened. I think the other cylinders that seemed dead were #4, #5, and #7 possibly more, nothing happened to the idle when those were pulled too. I know I have spark to all the cylinders because I hooked up my timing light to all of them, and it triggered. Could this be an issue with the carb, half of it not working properly due to the dual plane intake feeding different cylinders?
-Exhaust popping bad around 3k RPM. I think this has to do with the dead cylinders dumping too much fuel into the exhaust once the secondaries open and it is igniting in the exhaust.
My question is what kind of problem does this seem like and what's the best way to start investigating? I have a lot of experience with cars, but not too much with old carbed BBCs, I am learning as much as I can, and am enjoying it, but a lot of the research I have done has lead me to many different possible problems. Could it be a massive vacuum leak somewhere, rounded off cam, burnt/bent valves, bad valve guides, fuel issue in the carb with the dual plane intake? How can I investigate some possible "easy" solutions with the engine still in the car, and not having to take it all apart?
Any help is greatly appreciated!