Classic/Antique Car Repair: 74 nova part 3, fuel air mixture, spark plug wire

Question
 Hello again, before pulling heads off I checked compression from all 8 plug holes.  All seemed to be fine with a reading over 100+.  Does this insure me of no crack or gasket leak?  I have also pulled timing chain which seemed loose and replaced it and the gears.  I belive I got everything lined up correctly.  Now, since then I tried to turn it over and got a back fire from the carb.  I've been told before but what does this point too?  Thank for the help.

Answer
No, the compression is high enough that the engine should run OK, but it doesn't mean there is no leakage - when the engine is actually running, the pressure in the cylinder is much, much higher than what you read on the compression tester - so that isn't a good test for a bad gasket or sealing surface.

The backfire through the carburetor means that something is igniting the fuel/air mixture when an intake valve is open - which should never happen if everything is right with the engine.  The usual cause for this is the distributor being mis-timed;  I have to ask if the engine was turned at all with the distributor out since the last time it ran right?

Are you sure that you have the distributor in right - it is common to get it in 180 degrees off if you don't verify that the engine is on the compression stroke for #1 piston when you install the distributor (with the rotor pointed at #1 spark plug wire).  If you did not verify this, it's a good idea to double check. It was OK before, or else the car would not have run at all, but if you disturbed the setting while changing the timing gears and chain, it could be off by half a turn now.

The way to double check is to use your compression tester to tell you when #1 is on the compression stroke (pressure starts to build in the cylinder as you slowly turn the crank clockwise), then stop the crank exactly on the TDC mark (without overshooting and backing up), then pop off the distributor cap to see which plug wire it is pointing at - if it isn't pointing at #1 plug wire, pull the distributor and re-insert it so it lines up correctly when it is all the way seated.  That should eliminate the backfire.

None of this has anything to do with the moisture coming out the tailpipe, or the very feeble engine power.

Let me know what you find out, we'll go through this step by step until we find the problem.

Dick