i have a 64 283. it was all original until the carb puked, i put on an intake and holley 4bbl set up i had off of a different project. nothing extreme just a performer intake. car ran fine. it sat for a week and then upon start up ran like crap. i started pulling wires and 2 cylinders on each side aren't firing (4 total). i checked plugs, wires, cap, rotor, firing order and still the misfire. could it be valve seats from no lead additive? any help is greatly appreciated !!!
You said you checked them, do you mean visually? You may need to try to isolate the problem by working your way backwards. Check to see if you got fire to the plugs, then check to see if its firing out of the wires; then check to see if its firing out of the cap; you said its fireing on 2 cyl. so the coil seems to be getting to the cap. Good luck.
Ok, if your getting fire to all 8 but no boom then you have 1 out of the 3 things you need to make it run. Are you getting fuel into cylnder, check plugs? Then check to see if you jumped timing, see if #1 cylinder is on the compression stroke by "sticking finger in the hole" method while you have a friend bump the starter. DISCONNECT COIL WIRE PRIOR so engine doesnt start; then see if its at #1 on the rotor button. Remember you need air,fuel and spark in harmony. This is a good troubleshooting start.
First question which cylinders are not firing? It has to be every other cylinder in the firing order in order for the engine to start at all. That means they will not all be on one side of the engine (all odd numbered cylinders or all even numbered cylinders) which all but eliminates a fuel distribution promblem. That leaves compression (the heat part of the fire triangle of fuel oxygen and heat), and spark as the suspects, or air supply. You could have a cam going flat if you have a flat tappet cam as modern motor oil no longer has the escential suplementry metals added to it that are required to prevent accelerated wear on a flat tappet cam. That means that even though you see movement on the rocker it isn't opening the valve enough to let in air. A simple check is to push down on the rocker arms. If they move you have a flat cam as there should be no lash at all with a hydraulic cam.
If it isn't the valves then that leaves the ignition system. and your distributor and wires (I assume you have pulled all the plugs to verify the piston has not closed the spark gap by hitting the electrodes when you over reved the car's engine). You can OHM each wire to verify it has no excessive resistance. and you can visually check the distributor cap and rotor for cracks and contact damage (such as a bent rotor button).
cap, rotor, plugs, and wires, all brand new. the cylinders that arent firing are, on the driver side, the two in the middle. and on the passenger side the one closest to the front(radiator) and the one second to last(one in from the firewall) so its two together on one side, and every other one on the other side. cant check the valves right now cuz in ny, its in a cacoon under 4 feet of snow.
Vacuum leak at intake. start it up and use a propane torch (unlit) around the intake on the cylinders that aren't hitting...see if that will make them fire. just be careful. you can use your cutting torch also. nice to have a helper with an extinguisher handy too.
If the car was running and then sudenly it is not it is generally electrical with intermitent misfires as you describe.
Bent valves happen after over reving a running motor. If you didn't over the motor that scenario can be discounted. A worn cam doesn't appear all that quickly (it takes time to wear away a quarter of an inch of the lobe or lifter), so you will observe the car running steadily worse with every outing. A bent rotor button makes the car hard to start once it happens and causes backfiring as the car dies from mis fired plugs getting a spark siganl before they should. A cracked or carbon tracked distributor cap can be physically observed and is easy to replace.
A worn out distributor will give all kinds of problems electrically and often has symptoms as you describe but the cylinders that are dead will move araound as the shaft wobbles.
Bad wires will definitley exhibt the symptoms you are describing as the electrical voltage goes to ground before it gets to the plug. You will have to physically remove each wire and examine it closely for cuts or burn spots or any fiberglass showing at the terminal. The wires should also be OHmed to determine they are all continous and have not broken downb internally.
Fuel distribution problems in addition to leaving some cylinders lean and others rich cause visible smoke and frequent back fires as well as the smell of unburnt gasoline.
I suggest you take the car to a competent mechanic who knows what a distributor is and has seen points before. He should have a dwell meter in addition to an induction timing light to check your electrical system. It would be nice if he could check your coil in some manner besides OHMing the wires as they often break down only when heated or shaken.