engine cranks but won't run

[crzyc68]

Engine was running fine.  Then one day stopped running.  It will crank but won't run.  Have fuel and spark.  Engine is a 400 that I put in a 68 Charger.  Ignition system is MSD 6AL and MSD billet distributor w/ blaster 2 coil.  Carb is a Speed Demon 750 mechanical secondaries.  I have a holley electric fuel pump.  I have changed the ballast resistor and voltage regulator and fusible link and spark plugs.  I also am running a Pete Jackson quiet timing gear.  What would cause this to happen?  I have taken the carb off and cleaned it and checked the needles and floats to make sure they are working properly.  Any suggestions?  Drivetrain setup is 727/3.55 suregrip.  I keep searching for solutions on the internet and talking to people that have had this similar issue but nothing seems to work.  I am going to try a different carb tomorrow just for giggles.  Thanks in advance.

[ACUDANUT]

 Hard to tell with a MSD ignition. What's wrong with the factory electronic ignition ?

[elacruze]

Take the scientific approach.
If you have fuel, and you have spark, all you need is timing and compression.

It isn't likely that you've lost all your compression at once. It isn't likely that your timing got thrown off so far it won't run, unless something broke in the distributor drive. That's easy to check, see that the rotor turns and that you can't turn it by hand beyond the mechanical advance.

If that checks out, pull a plug or two and see if they're fouled. I think that's most likely. It is possible that the MSD is failing, but I think it unlikely.

[FLG]

I see a small problem, if your running and msd system why do you have a ballast resistor 

[six-tee-nine]

I'm with elacruze......

If you are sure you have a spark and and fuel then my guess is check your timing chain. or your distributor hold down clamp. (timing might be way of).

BTW you have spark you say? Is that a bright whit/blue-ish spark or a yellow/orange one? The last one is the one you dont want. It could indicate an ignition system failure.
I've seen plugs spark orange very well in the open but when under pressure in the bore the spark just got blown away by the compression pressure.

[crzyc68]

The ballast resistor is for the charging system.  Is it not supposed to be in the equation?  Like I said it was running fine for a while before it stopped.

[FLG]

The voltage regulator is for the charging system.

The ballast resistor is for the ignition system, it lowers the coil voltage to 8v or so while the car is running. A msd ignition will eliminate the ballast resistor. Double check all your wiring.

[crzyc68]

To eliminate the ballast, do I just install a jumper between the wires that are connected to the ballast?

[FLG]

First lets get things straight. If you search the site youll get a bunch of wiring diagrams for it.

How is it currently wired?

[BigBlockSam]

 

[crzyc68]

Spliced the wires that were attached to the ballast together and it started right up.  This site is awesome.  Can anyone tell me why the car started and ran when the ballast was in the loop?