cantorhome

I've got a '67 200 motor. The spark is orange, and I understand it's supposed to be blue (meaning when I arc the spark straight from the coil to the block, using the plug wire that I disconnected from the center of the distributor cap), which indicates a weak spark. At that point in the circuit, it's before the distributor, narrowing down the search somewhat.

The battery is 2 months old.

I tested the coil:

• Between the positive and negative side terminals, I'm getting 1.1 ohms (is that too much resistance?).
• Between either side terminal and the center hole, I'm getting 10,650 ohms.
• Between the negative terminal and the coil body (ground), I'm getting 44 ohms. The only wire connected to that negative terminal goes to the Pertronix unit, and that wire shows no connection to ground when it's removed from the coil.
• The positive terminal has 6.0 volts with the ignition on.

One bit of info I found online gives a formula for calculating the maximum amperage in the ignition system (formula is 6.0 volts divided by 1.1 ohms). That shows 5.5 amps, which that online source said is too high for 4- and 6-cylinder engines (max supposedly should be 4 amps, and for 8-cylinder max is 8 amps). That source recommended installing a ballast resistor. I have no idea how trustworthy that recommendation is, or if it's relevant to the weak spark issue.

Do the numbers above indicate a problem with the coil?
Any other ideas about what could be causing the weak spark?

Gun Jam

what is it doing to make you start hunting for problems and suspecting things like possible weak spark??


are you running points still?

-Gun

cantorhome

Pertronix. It's running poorly, but I'm focusing on the weak spark right now and nothing else.

musnicki

Check each wire, make sure that they don't go above 100ohms. Depending on your wires, they run about 40-50ohms per a foot. Go cheapest to most expensive. After that I would pop your distro cap off and take a look at the contacts and the spinny thing in the center. Sometimes water can get under there and rust out your stuff a little....and then look at the plugs...maybe buy one or two and switch them out to see if you colour comes back, if that's the case then change all 8..er 6 out. Lastly, look a replacing your coil. It's mounted on your fire wall, correct? I ask because I mounted mine on the head and I guess the heat affected it.

Or...do like Gun Jam said, is it still running good? Don't smell too much gas in the pipes? No back fires? Still have full power? Plugs not fouled? Then your "stuff" running good. If you're not getting that "full burn" then you'll smell and maybe see that extra not-burned-gas come out the rear end, you'll also have diminished power, you'll get some back fires (un-burned gas burning up in the headers and exhaust pipes) and...oh...your plugs will be dis-coloured. Google a spark plug chart (I'm too lazy to link one) and see what your plugs compare to on the chart.

James

cantorhome

Thanks. How do I check the ohms on the plug wires? I tried checking ohms between the connectors at each end, but got no connection at all - presumably because of the way the wire conductor never makes contact with either end, just wraps around and gets squished.

The problem is pre-distributor. The orange spark is coming directly from the coil, when I arc the coil's outgoing plug wire against the block. The block is mounted against the head on mine, just aft of the fuel pump.

The car runs poorly, and after tuning everything properly, having the head completely rebuilt, rebuilding the carb (x4), I'm down to weak spark. By poorly, I mean a previous owner had disconnected the automatic choke, and set the choke adjustment so the carb was always choked. When I corrected that by hooking up the choke pipe to the exhaust again, I discovered the car will only run when it's choked. Anyway, back to the weak spark...

Gun Jam

To check Ohms set your meter to horseshoe setting, select one wire put test probe in one end and the other test probe in the other, look at the meter's screen and it will tell you how many horseshoes there are in that wire. Make sure the test probes make good contact with the wire terminals.

When you arc the coil lead to the block how far does the spark jump? over 1 inch?
The further the spark jumps the less blue it will appear if I recall correctly. Despite what color it may be if it can make a 1 inch jump there is no issue.

-Gun