Weak Spark

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Model T Ford Forum: Forum 2012: Weak Spark
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff Statham on Friday, August 03, 2012 - 10:59 pm:

I seem to have an equally weak spark across all 4 cylinders of my '21 T. I've changed the timer and it didn't help. All the wires are clean and tight. The coils seem to be buzzing fine - and give me a light jolt when I hold the points down.

If I short the plug to the cylinder with a screw driver - I barely have 1/8th inch of spark.

It doesn't seem to make a difference weather I'm running on mag or battery - it has low power and lots of missing. Once I get up to speed though - it's not too bad.

Any suggestions?

Thanks
Jeff


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen D Heatherly on Friday, August 03, 2012 - 11:06 pm:

Have you ever had your coils rebuilt?

Stephen


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Saturday, August 04, 2012 - 01:06 am:

Jeff,
If you are shorting the spark plug wire to ground when the wire is connected to the plug, then 1/8" would seem about right. The spark will take the easiest route, either to the screw driver or spark across the spark plug electrodes.

One word of caution, don't try to test the spark out of your coils with any gap more then about 1/4". If you do you can ruin a otherwise good coil because it may make a non-repairable carbon track to ground inside the coil.

How does it run?

The real test for the coils is on a hand crank coil tester (HCCT) or strobo-spark tester.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Saturday, August 04, 2012 - 02:59 am:

Check the connections at the terminal block on the firewall.......as far I have seen most originals have served well beyond their useful (dependable) lives.
I'm replacing a fourth one as soon as I have time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Saturday, August 04, 2012 - 08:42 am:

Sorry, I missed the "it has low power and lots of missing". Just have to go through the basics, check, the coils, spark pugs, wiring, fuel and air supply, compression and timing. Something sounds like it is not right.
Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Saturday, August 04, 2012 - 09:16 am:

I regularly check the performance of each cylinder by holding the coil points down and listening for the change in engine speed but I never get a jolt when doing so. Could that possibly be an indication that there is a problem in the coil box?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Saturday, August 04, 2012 - 09:37 am:

Coils first Jeff. Especially if they've never been done. You don't mention if this is a new development or it's been running this way for a while but still.. It's possible you'll eliminate the problem having them done but beyond that it'll run much better over all if you do.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Saturday, August 04, 2012 - 10:50 am:

You on't get a jolt from holding the points down on a coil. There is only coil input voltage up there.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, August 04, 2012 - 11:31 am:

If you have another T, or know someone who has a T, and that other T is running just fine, try swapping the coils. If your coils run just fine in the other T, your problem would not likely be the coils. If the coils from the other T run the same in your T as your coils did, the problem is somewhere else. It could be low compression which would be caused by bad valves and or rings. If the compression is good, It could be the timing is not set correctly. Or you could have a fuel starvation problem. Since it runs better at higher speeds, it is not likely fuel starvation, but could be a clog in the low speed passages in the carburetor.

Another possibility for problems is in the coil box. It could have a carbon path burnt into the wood, or the contacts not good between the spring contacts and the coils. I am thinking that your problem just might be in the coil box or coils, because you shouldn't get a jolt when you hold down the points. They are only operating at low voltage and when you hold down the points.

Another possibility could be a timer problem. This could range from being dirty, have a weak spring, be off center, or timed incorrectly. If you have the new day type timer, the brush could be worn out and not making good contact with the cap.

Have fun checking out everything. Sometimes it takes a while to find the problem. Check one thing at a time and don't get discouraged.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff Statham on Saturday, August 04, 2012 - 01:14 pm:

Wow! Thanks for all the suggestion guys. I'm almost 43 years old and I've owned a T since I was 15. I never usually have trouble fixing it but this problem had me puzzled. It took 3 hours for a 2 hour drive last weekend!

I do have a New Day timer but it's clean inside and the brush is fairly new with not a lot of miles on it

I'm also thinking that it may be a coil box problem. It still has the original guts in it so maybe it's time for a rebuild.

Thanks!!


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