Weak Spark Problem

JimTravis

JimTravis

Member
What would be the most probable cause for a week spark? With the plug out and grounded to engine, the Spark in a dark shop appears to be extremely weak. I have put this motor together from various parts I have had laying around so nothing is "known to be good" . I did eliminate the coil as a problem by putting a new one on. Again- I am getting a spark but it is very faint and the engine will not fire. Thanks
 
It's hard to tell by eye, use a spark tester. If you don't have one take an old plug, widen the gap to about 1/4 " and retest the way you are doing. If it jumps a large gap it's not weak.
 
Have you tried replacing the condenser? It could be failing. And how are your points, and the point gap?
 
There is a certain way to connect the coil with plus to one side and minus to the other. If connected backwards it can lead to weak spark.

Coils are usually marked. Frequently because of the upside down condition of the Model A mount, the markings can't be seen and get ignored.

Joe K
 
start with a LOGICAL system of trouble shooting and stop dive bombing by trying this and that.. Start at the battery, check the connections, ground, volts on the battery, then move to the starter, and all the way up., IF you follow the primary circuit in Les Andrews Blue book on the electrical system you will find the problem. Just don't go here and there and keep trying this and that..logical trouble shooting and you will find it..good luck
 
Make sure the coil wire is solid wire and not a modern carbon wire.
Hold the coil wire about 1/4" from a head nut and see if you have a strong bluw spark.
Stop the engine with the points open, then short across them with a screwdriver off-on, off -on, etc. to check for a good spark. If you now have a good spark, the points probably need to be cleaned.
You need at least 5 volts at the coil while cranking and 6 while running. If it's less, you may have loose or dirty connections.
 
Thanks for all the reply's. I can put aside a couple suggestions,. The battery is strong and the connections are good. The coil is connected properly (+ and -) . I filed the points and set the gap. The coil wire is something I have not checked and the condenser - I don't know how the check it. I think I have a new set of points that I can put in and I will check for proper type of coil wire. The suggestion of opening the gap for checking the strength of the spark is good and I will do that.
I'll let you know how this works out.
Jim
 
Jim,,

1. First if you do not have one, please get a Multi-meter -- very inexpensive, but better than aspirin for relieving Model A headaches.

2. Mr. Marron's reply #2 & #7 are really a great way to check electrical problems, i. e. starting with the battery, and methodically following the wires all the way to the end.

3. Trying not to sound like a broken record, current flows from your battery through wires just like water current flows through water pipes.

4. One bad electrical connection in a wire, like at the coil, the junction box, condenser etc., etc., or an exposed un-insulated wire touching metal, (i.e., grounding out), & the flow of electrical current is impeded, whereby this loss of current flow is similar to a water leak in a water pipe which decreases the flow of water at the end of the pipe.

5. All of the other suggestions are similar & most noteworthy indicating to check good electrical current flow.
 
H. L. Chauvin said:
Jim,,

1. First if you do not have one, please get a Multi-meter -- very inexpensive, but better than aspirin for relieving Model A headaches.

2. Mr. Marron's reply #2 & #7 are really a great way to check electrical problems, i. e. starting with the battery, and methodically following the wires all the way to the end.

3. Trying not to sound like a broken record, current flows from your battery through wires just like water current flows through water pipes.

4. One bad electrical connection in a wire, like at the coil, the junction box, condenser etc., etc., or an exposed un-insulated wire touching metal, (i.e., grounding out), & the flow of electrical current is impeded, whereby this loss of current flow is similar to a water leak in a water pipe which decreases the flow of water at the end of the pipe.

5. All of the other suggestions are similar & most noteworthy indicating to check good electrical current flow.
Click to expand...

Right on..I would add, make sure you have the engine grounded to the frame, and battery. without a good ground, you can't get good current flow.
 
I would change the condenser. It is almost always the problem and the cost is low. I only use the burnout proof condensers now sold by the reputable parts suppliers. I have replaced some with NORS swap meet condensers and found many of them to be bad out of the box.
 
Per your suggestions, I have checked all connections and found them the be good ( yes Rock I have a multi-meter ) from the battery through the distributor. I have ordered a new set of points and condenser so hopefully that will solve the problem. I really think the condenser is the problem but I thought that with a bad condenser I would get "no" spark instead of a "weak" one. I'll let you know how I make-out.
Jim
 
midgetracer said:
I would change the condenser. It is almost always the problem and the cost is low. I only use the burnout proof condensers now sold by the reputable parts suppliers. I have replaced some with NORS swap meet condensers and found many of them to be bad out of the box.
Click to expand...


THAT is DIVE BOMBING to find a problem that you have no idea if it exists. Seems everyone who does not follow a logical trouble shooting method always says..Change the condenser...WHY??? does he have a good battery connection, ground, spark, fuel, spark.. if he has a strong spark why change the condenser... That is not the way to find the problem and, all I am saying is follow a simple step by step method to find it and you will. It is ONLY a primary and secondary circuit.
 
When you grounded the spark plug to the engine, was it to bare metal, or through paint, rust, crud etc? While you are at it, clean out the plug threads in the head with carb cleaner and a paper towel.
 
Did you clean the point after you filed them? A little oil on the contacts from the file could be the problem.
 
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