The other day I was driving my 26 T to a car show. 5 miles down the road, it began to backfire bad on the mag side. I drove home on the battery side of the switch. Later I tested the Mag post. Using a 1156 bulb, along with an analog tester. Had 2.5 volts at idle, and about 7 at half throttle. I guess it was time to recharge the magnets. Set up batteries & cables for 36 volts. Rotated it for the compass to point north toward the front. ( I read every post I could find.) First start the test bulb was dim, after a second it brightened up. I switched to the mag, She ran fine. While running I took off the test light, and she died. I started on bat. switch to mag, will not run. Back to the same situation. Low voltage. What keeps draining the magnets. The mag post was taken out & cleaned & checked for shorts. Seems fine. Checked wiring to the switch, no grounds. Dan C.
Something other than weak magnets is causing the poor magneto output.
Ron the Coilman
Maybe I need a new magneto coil.
Check for battery voltage at the magneto post. Could be a wiring or switch issue messing up the magnets. If no battery voltage is present, then you may have a coil ring problem.
If the coil ring has issues, I don't see how an in car recharge can work properly since a good coil ring is needed to get charge into the magnets.
Just because it's easy to do, try enriching the mixture (Airplane engines will occasionally backfire when leaned out too much). Hey, ya never know.
Before changing the magneto coil ring Watch for play on the crankshaft. If the distance between the magnets and the coil ring is to far you will have a weak magneto. See also the article I add.
If you cannot read it just send me a mail, I will send you the originals.
I had a bad ignition switch in my 26 that was shorting out the battery to the magneto. It ran on battery and poorly on magneto. over a week, the magneto died. I also got some backfiring and other things when it happenned. I had the switch fixed and it's been fine since. I did have to recharge the magnets.
I had the switch apart & sanded the contacts 7 made sure they were ok. Everything from switch to coils is good, otherwise it wouldn't run on battery. Magneto voltage is low again after recharge. It will stay running on mag just after the recharge, as soon as I take the 1156 bulb off, she dies and low voltage again.
It may be an intermittent connection Dan. About the only thing you can do in-car is to remove the terminal assembly off the hogshead and check to see if there's a good solder blob on the coilring below, and also make sure the plunger or spring that makes contact with the solder is in good shape. Other than this you'd have to do a tear-down.
I had the mag post off and cleaned and tested for good contact. It's a post with oil line. Dan
Be sure the oil line is not inserted too deeply into the magneto post and shorting out the magneto output. Very common problem.
Ron the Coilman
How did you have the test bulb connected? You say "first start the bulb was dim, after a second it brightened up" "while running I took off the test lamp she died"
In order to remove the test lamp you would need to unscrew the connection at the mag post unless the bulb was connected with a clip. That bulb should have been connected from the mag post to ground. No other connection should have been made to the bulb except for the voltmeter.
If the engine died when you removed the test lamp, something different happened. It should run on mag just as will with or without the test lamp. Are you sure that you didn't have one side of the lamp connected to battery?
My 1157 bulb has clips which were clipped to the mag post and ground. My volt meter tested between the post mag post and ground while the bulb was in place. I just tried to recharge the magnets, no go. Plan to remove the motor this weekend and put in a new mag coil. The fitting has a shoulder. It can only go in so deep.
I see you say you used a 1156 and 1157 test lamps, Iím not sure which one you used or how that would change your test results!
Not sure what mistake you are making but if the car runs on mag till you disconnect the bulb and then the car dies and all the time you are running on mag then that makes no sense at all since you are removing the bulb from the magneto which is removing some of the load on the magneto which would make it stronger yet you claim it dies at that point. If that actually happens then you need to seriously check your wiring and/or exactly what you are doing when you attach and disconnect the bulb since it would seem you are also disconnecting something else at the same time or possibly shorting the magneto out at that time.
It sounds as if the bulb is completing a circuit somehow and the circuit is broken when the bulb is disconnected.
The post is easy but where did you connect to ground?
LOL I just thought of something - I wonder if the alligator clip is squeezing the mag post connection enough to help it make good contact
Sorry for the mistake. It is a 1156 bulb.
Sounds like something shorting the mag post to ground.
Do check out all of your wiring and switch as JR recommends. Be careful to never let battery voltage criss-cross with mag voltage as you will then 'kill' the magneto.
Excellent graphics were made on the 26-27 arrangement by Robb Wolff. They can be found here
Do you have an original type magneto connection, or a magneto oiler? Some of the oiler types can have problems with grounding out, or not making good connection with the magneto button inside the magneto. I would suggest that you try a different magneto post before disassembling the engine to replace the magneto ring. If it is the post, you will have saved yourself a lot of unnecessary work.
In reading the above posts again, I see that you do have the post with an oil line. Best fix would be to add a few drops of solder to the button, but you would need to remove the hogs head to do that. Sometimes you can extend the plunger a little by using washers inside the plug to lower it a bit. Or a few drops of solder on the end of the plunger to extend it to the button. If it were mine, I'd try that first and then if that doesn't work remove the hogs head and extend the solder on the button.
I'd remove the hogshead as a last resort. That thing is a PAIN to take off and then re-install so that it is sealed well. I've removed it, re-installed it, then removed it again recently so maybe I'm a little biased due to recent trauma.
I'm go try another mag post. I checked the depth with a depth gauge and mic. I have about 1/8" of compression on the point when tight, so the tip is touching enough.
Just an update. The mag post didn't help. Removed motor and mounted on the stand. Removed pan and transmission. Ordered recharged magnet, spools, and screws. On checking the trans. Loose driven plate rivets. Oh good! Better check extra good. Loose screw in driven plate holding the clutch pack.Not much movement in bushings, except in triple gears. Found a tooth missing in the triple gears. On closer inspection on the backside of the gear, the broken tooth had been ground down to eliminate sharp edges. Nice job! Ordered necessary parts. Some of this might have been the problem with my free neutral. Oh yes I have a rebuilt Mag coil. Also I finally got a pic in my profile.