T misses on mag?

Kelly mt

Kelly mt

Member
I just bought a '26 T Roadster the other day and it runs great on battery but misses on the mag. RPM doesn't matter, it misses the same. It's set up with a 12v pos ground. The wiring is suspect so I'll run through it to see what's been done. My TT has a distributor so I'm new to the mag game. Any ideas? Thanks PK.
 

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use a voltmeter on the mag post and see what the AC voltage reads, let us know and we can go from there. The batt./ mag. switch could have poor contact also.
 
Try removing the mag post. Sometimes band debris get caught there causing this problem.....don't ask....LouB.
 
I thought if debris was under the mag post it would not run at all on the magneto. Running poorly could be the unit is not producing enough voltage.
 
Thanks for the reply. I'll check it tonight and get back. As to the 12v battery, I was scratching my head on that one. PK
 
The magneto is ac and does not care which way the ground from the battery is hooked up. If he has a gen. it will need to be re-polarized if he has an alternator is would need to be changed if he changes the ground to negative. Many Model T's have been run with positive ground with no ill effect.
 
I did a check tonight. At first I got 8v AC at high rpm at the mag terminal. I pulled the leads and checked some wiring then went back to the mag. I got 29V AC at high RPM that time. I then moved to the mag lead at the terminal block and now can't get more than 10v AC at either terminal. I'll have to check more tomorrow. PK
 
Make sure you use an analog (needle type) of meter as a digital meter doesn't like the home made AC too well. Even the AC voltage will show a wild frequency variation with engine speed. A lot of guys use a single filament bulb in the circuit for testing to simulate coil load; Ive always just used a meter for a rough output range. It either works or it doesn't. BTW... you've got a loose/dirty connection on the terminal block. I really get a kick out of annoying the judges LOL... ws

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I pulled the mag terminal out and found nothing, all clean. The spring worked freely and the contact is in good shape. The insulated terminal post did rotate inside the body, normal? I still get 8v AC at the terminal and the motor misses on mag. PK
 
Don't be surprised if that mag plug leaks a fair amount of oil when warmed up. Pull the plug and check with an ohm meter while turning it. make be bad internally. ws
 
I had a simaler problem with my 1913 turned out to be loose connections in my coilbox switch and poor coil connector contacts in the coil box
 
Well it definitely has leaked oil in this area. I'll pull it and check continuity, forgot to do that. I haven't even messed with the coil box or switch yet, next check. According to my manual, the wires are not laid down on the correct terminals on the terminal block. Haying is getting in the way of this important work! Thanks PK.
 
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