running on mag is problematic

[NY John T]

Hi all,
Last week I was able to finally take the 27 Tudor (barn find) out for a ride. When I switched from bat (it ran smoothly) to mag, it started backfiring and running very roughly. When I switched back to bat it ran smoothly again. Any ideas as to what might cause this or what I should start looking at? Thanks.
John

[BobShirleyAtlantaTx]

My first step would be to measure the voltage at the mag plug—should read 15+ at a fast idle. The volts by are ac the way. A fluke meter is great for this. Call if I can help, Bob @ 903-824-1949.

[JTT3]

Bob i agree, my experience with this type situation are mainly 3 big ones, poor magnet gauss levels, gap between magnets to field coil out of tolerance including 3rd main tolerance and loose/lost magnet keepers & or broken magnets. There are others but these are the big ones that may require and engine removal.

On the easy side
Loose mag wire to switch/coil box or even the switch tabs inside the case

[Norman Kling]

The output of the mag could be OK, however, be sure to move the spark lever up and down to find the sweet spot. And if the coils are not tuned properly, you could have a timing problem on mag, because the coil fires as the voltage rises and it is able to draw 1.5 amps current. If one or more coils is not adjusted correctly, they could run smoother on battery than on magneto, however when everything is tuned, it will run better on magneto than battery. By the way, the problem could even be a timer problem. So first I would check the magneto output. If it is low it is a major job to fix it. However if it is a coil adjustment or timer problem, less difficult to fix.
I would recommend you obtain the booklet on "Electrical System" which the club publishes.
Norm

[speedytinc]

Sudden. Pull the mag contact & clean off the wad of built up band fuzz.

[NY John T]

Hi All,
I'll try all those suggestions and get back to the forum with my results. Thanks so much for the help.
Joh

[John kuehn]

Clean the mag contact and ck out your ignition switch first then ck the other that’s mentioned. The contacts inside the ignition switch could need cleaning up or slightly bend the contact on the mag side when it’s on the mag side.
Make sure you go through the obvious things first. If it still acts up remove the transmission cover and visually inspect the mag ring as best as you can for anything that looks loose on the coils. You won’t see all of them but at least you can check some.

[Ron Patterson]

John
Your description of problem has the classic symptoms of poorly adjusted ignition coils.
Try to find a local friend that has a known set of good coils that have been properly rebuilt and operate well on Magneto.
Try them in your car and see what happens.
Ron Patterson

[nicklm]

I had the same kind of a problem and found that it was a loose screw on the terminal block on our fire wall.
Tightening the screw corrected the mag skipping. If could be something simple too.

[NY John T]

Hi Ron,
Good idea. However all the coils are ones that you rebuilt; so I'm sure that they're all working fine. Thanks,
John

[DickC]

The MAG is problematic!!!! I recently opened the hogs head to adjust the high speed clutch. As I removed the cover and the filter, something fell out of the filter and plinked to the bottom of the transmission. A light revealed the small bar that holds the magnets. The net result was to remove the engine and drop the pan to insect the mag. I found another keeper and also found that several others were loose. This message is to suggest that everyone should check the mag and ensure the keepers are there and TIGHT. I was lucky. A loose magnet can destroy and engine quickly.