34’ - Weak Spark Troubleshooting

[dbtenner]

Hey I would like some assistance and have other opinions. I’ll start from the beginning and try to make this brief...

In December last year I had an issue where my condenser played out, no problem I changed it out. Then in March I had an issue where I was misfiring. I had it looked at by an individual and he noticed I had a very weak spark and suggested that I have the distributor and coil rebuilt but he went ahead and cleaned the spark plugs and drove fine. Now 8 months later, I am noticing the same symptom where it appears to be missing occasionally and lots of carbon built up on the plugs just as in March.

Here is my opinion, either....
1. The condenser I changed out isn’t rated for a Model B and that is the reason for a weak spark. I have a spare condenser of a different brand that I’ll swap this weekend to see. Is there a rating I can check for on my voltmeter to make sure it’s fine?

2. What should the voltage be at the end of the ignition wire that on the coil? It could be that the resistor is too much. This is a variable that has not been changed so I doubt it.

3. The distributor may need to be rebuilt, it’s delivering a weak spark which it unable to detonate at higher temperature this leading to high carbon deposits on the spark plug. I checked the spark yesterday and it was barely nothing as I grounded it to header. Not good spark.

4. The coil may need to be rebuilt.


I have gone ahead and cleaned the plugs and reinstalled it. I’ll test to see if it runs smoother and if I have a better spark when I ground the spark plug.

Please weigh in on which opinion you agree with. Thanks!!!


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[Ken/Alabama]

Check the ignition switch itself . They get burned and corroded over time and will cause a high resistance to the ignition system. Easy to disassemble and clean.

[Terry,OH]

There are a lot of areas you should look at to ensure the voltage to the coil is as high as possible: Battery, Battery cables, wire connections to all ignition terminals, ignition switch. It is also a good idea to have the coil rebuilt and if the distributor has not been cleaned and serviced for years have that done, especially if you drive your car and want peak performance. If you send the distributor and inner caps, coil, and condenser to Bubba (here on this web page) he can have your coil rebuilt and ensure all the components are in peak condition. Check the ignition wires for zero ohms end to end. What spark plugs are you using? What Carburetor, since lots of carbon can be caused by the Carb. delivering too much fuel?

[rockfla]

I had the same trouble with our 39 Merc that I just recently fixed. The volt at the coil at one point dropped below 3 to 2.7V. First I started, as stated above, with cleaning the battery post and terminals really good. Next I pulled every battery cable from the car and cleaned and used dielectric grease on all the positive, negative and ANY other ground strap I could find. Then did the same from the inside of the car from the ignition switch out and cleaned all connection points. NOW I am getting readings as high as 5.4 to 5.5 volts. Also had the coil redone by Skip Haney and had the distributor clean, rebuilt and set up on a Sun machine by a local friend. ALSO installed a new condenser from NAPA.

[tubman]

As to checking your condenser with "voltmeter" (multi-meter), most meters have no provision for this. Suitable meters are available, but are quite expensive and most people don't have one. Even if you have the proper meter, the condenser may test just fine cold, but will deteriorate when it heats up or just though being cycled multiple times.

[AnthonyG]

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Here’s a thought, I mention cause it bit me. Do u have an external resistor, possibly installed during refresh or resto work? I did & forgot to disconnect original resistor from circuit doubling the resistance. Same symptoms.

[B-O-B]

This is just me & what I would do. Send the dizzy & coil to Skip & have them redone. He does a great job & his turn around time is quick , also reasonable. Open your hood @ night & see if your coil &plug wires are shorting out,/sparking. I also use NGK plugs. My engine is 6V, didn't catch what yours is but being a model B I assume it is also 6V.

[koates]

You make mention of Model B, so is your car a 4 cylinder or a V8 and what year is it, 1934 ? Model B is only a 4 cylinder. Regards, Kevin.