Too simple of a question?
I have spark on all four plugs, but they seem equally weak. Pulling the plugs & laying then on the head, I see all four spark but only barely while turning it over. Nothing like I see on chainsaws, lawnmowers, Camry, etc. Should I expect a big, white, gap-filling 'man that would hurt' burst or just a little blue thing?
Details: 1927 Tudor. 6V. Texas T distributor, new NAPA coil, resistor available but unused, unknown condenser status.
How well does it run, or is that why you ask the question?
Its not running, but for multiple reasons. I'm trying to go through them one by one.
The spark on a coil tester is a long bright spark.
Those VW distributors had a problem of not earthing well, you will need an earth wire from the body of the distributor to the engine.
You can buy an inexpensive adjustable tester that works for a small engine or a car. The gap is marked for any engine. Many small engines are hard to see a spark without one. Think I got mine at NAPA
Laying a plug on the engine and analysis of what you see at the plug proves nothing since the plug is then in free air and it takes about 1/4 of the voltage in free air to spark a plug but under compression it will need a lot more power. I would suggest you rig up a gap of 1/4" wide exactly using a block of wood and spark gap made from sheet metal or coat hanger. Then hook your spark plug wire to that gap in air and retest your spark energy. If the voltage reliably jumps that 1/4" gap then move on to other issues to test. Do not make the gap wider than 1/4" if you are testing coil/timer spark since that can cause the spark to jump inside the coil and damage to the coil is likely.
Assuming it's a coil rated at 6 volts. Make sure it doesn't have a built in resistor too. If it does don't add an external one. Both things should be marked on the body of the coil. Check the voltage going into the coil just to make sure it's 6 volts. Add a ground wire to the dist. body. From the part that rotates to ground somewhere on the block. Clean/re-set the points. If no change replace the condenser. Spark should be somewhat "robust" & as John said a 1/4" gap should be jumpable. Easiest? just hold a disconnected plug wire to ground and have wifey crank it. Or, depending on your marital status, have her hold the wire.
Thank you for the replies.
I figured it was the coil, but as I go through 3 of them I see little difference. It definitely won't jump .25". Perhaps I have dud coils. Next I'll buy a Petronix 40011 from Amazon (and condenser while I'm at it).
Yes, the coil is rated for 6V, tests 2-3 Ohms, internally resisted. No external resistor added. 6V battery fully charged. I added a separate distributor ground wire. Points clean & gapped .018; the gap's circuit works as expected (opens, closes w/ nil resistance). I have an inline plug / coil tester... just need enough ooomph to make it work.
Try that extra ground wire and if it don't cure it, stop in at napa (or others) and pick up the EP466 condenser for that Bosch.
If you leave that new condenser on your regular car and it falls off, don't run it over like I did.
IF the inline spark test thing is simply a gap in the wire then be sure you include that gap as part of your 1/4" total gap for tests and then get rid of it for actual starting/running. Why not try a new condenser first since I would expect the pertronix setup to act the same or give you less since it adds no energy to the coil it is used with and is just a solid state set of points in function. I have that setup on my wife's Mustang and it runs great with stock coil but its fame is based upon reliable ignition - not a hotter spark unless you also are going to change the coil. If you use the same coil with the solid state pertronix the result will not change. If your car has a slow cranking starter or weak battery you might simply have too light of battery cables and/or not supplying full 6V at the primary DURING CRANKING. The power tap for the car comes from the foot starter switch and directly from the battery and if you have light battery cables the primary voltage to the coil will be low since the ignition fires at/near peak compression which is also the point at which the starter current is at a peak and coil voltage might be near its lowest voltage. I don't think there is anything wrong with your points or distributor nor possibly even your coils since you have tried 3 of them.