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weak spark troubleshooting

21717 Views 1 Reply 2 Participants Last post by  bill z
Weak Spark – things to check first

this is for any of you that have anemic spark and are having hard starts.

I'd like to relate the experience I saw with my latest project, a 63 4000 RC.

I got her at auction, had a bear of a time starting her.. weak to non existant spark.. had to have the jumper buggy jump her and I had to jumper out the ignition resistor just to get her to barely start... left her running during the auction so whoever got her could get her trailered..

I may have already posted this.. but here is what I found when i investigated the ignition.

wire to/from the key switch was 1/8" coax using the ground braid.. had a ignition resistor and a 6v coil, and a alternator setup as 1 wire that didn't charge (apparrently)

wire connectors were old loose, and one at the resistor had only a single strand actually making contact. coil was an older dry type, not oil filled.. looked like it had been hot before as it was cracked at the top.

plugs were old and rusty.. and 2 came out by hand ?( threads fine,.. just loose.. ) spark plug wires were some foriegn car looking wires.

cap was older, but pristine inside.. to tracking or apparrent waer.. same with rotor and points.. I didn't even change them.. they were dead balls on.. did lube the cam.

new plugs, new wires, new primary wire, new napa ic14sb coil, and no resistor and she pops off before you can let go of the thumb switch, NO choke.

I know we see lots of spark related problems on the board, and lots of point changing.. etc.

My advice is to make sure everything is perfect BEFORE the distribuitor, before you whipn out the feeler gauges..

20$ of plugs and wires and some connectors turned a sputtering non starting auction tractor into one that starts as good as a modern automobile...

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A couple of things I would like to add based on a few years of working on engines.

Don’t skimp on the wire that connects the battery to the coil. The coil needs current to work well. When strands break off, it cuts the current down some. Think about how much water comes out of a fire hose than a garden hose.

Most all coils from way back require a dropping resister to reduce the voltage to them so they won’t burn out. I guess a hold over from the 6 volt days. Some of the high compression engines had a switch on the starter solenoid that would go around the resister when the starter was in use to give extra voltage only at start. Running a coil that way for very long will burn it out.

Electricity will follow the path of least resistance. If that is within the distributor cap, then that is where it will go if there is too much resistance through the plug wires, through the plugs and to the block (like loose rusty plugs).

I just love this part of an engine. My Deere has a mag but electricity is still electricity.
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