1930 a w/12v conv. won't start

J

justcruisin68

Junior Member
just converted my 1930 model a to 12 volt negative gnd and can't
get it to start...it just backfires out the carb. never messed with
timing. double checked all wiring....has single wire alt..coil with
external resister..reversed wires on 30 amp. ampmeter...what did
i do wrong, other than converting to 12 volt negative?
any help would really be appreciated...thanks
 
A few things come to my mind: Did you remember to also change the coil polarity? If yes, then: Check the voltage from each terminal box nut to ground while cranking. The readings should be the same, 9+ volts, then back to 12+ when starter is released. If not both the same, you have a problem inside or external to the ammeter wiring. If below 9+ volts, you have a problem with battery cable connections, four ends to check! If that is all OK, you may now have more spark energy than a dirty dizzy cap and body can handle without crossfire. Scrub the inside of both with detergent and a scotchbrite pad, dry and try. Next: Your capacitor may have gave up the ghost. Try another. Next: The coil may be intermittent. move the brass plug connectors each 1/8" off the dizzy cap and check for sparks in the proper order while cranking. The obvious: Gas- you did open the valve???? Plugs clean and dry, engine not flooded from all that cranking? Timing: it may have actually been rather retarded and capable of starting on slow 6V crank, but now your timing errors are coming back to haunt you? Try cranking with the lever 1/4 down. If it starts there, your timing is screwed up. Square one, back to the pin and TDC. Fishing: maybe the fiber cam gear is shot. Maybe the manifold gasket called it quits.
 
Are you using a 6V coil or a 12V coil? On my cars I am still using the 6V coil, I added the ballast resistor to step down the 12V to 6V on the coil. Would it make a difference if you are using a 12V with a ballast resistor dropping it down to 6V on a 12V coil. I am not sure but Are you still suppose to use a ballast resistor if using a 12V coil on a 12V system? Anyone know?
hope this makes sence.
 
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I would re-check the timing just to make sure that it is ok. I agree with MikeK that it may have been off when you were 6V, but was still working.

The coil should work either way the polarity is, but will have a weaker spark if it's backwards. I'm not saying it's ok to have a reversed polarity coil. I'm just saying that a reversed polarity will not prevent the car from starting. Make sure your polarity is correct and you will have a hotter spark.

And yes. Check the obvious. Did you forget to put the rotor back in? Did the coil to distributor wire contacts come loose? If you removed the gauge panel and messed with the ammeter. Is a wire on your ignition switch or ammeter now grounding against the gas tank? If you have a fuse on your starter, did it blow or come loose when messing with (pulling on) the wiring to the Alternator?
 
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