Starter works on bench but doesn't when hooked up on tractor

[Andy M]

Are your starter cables small automotive type? 6v needs the larger cables, I think it #2AWG. Small diameter wire makes the starter turn slower.

I've got #2AWG cables.

[Andy M]

Bad field coils or armature.--is armature shiny? brushes new/clean? bushings worn? This does affect performance.---since you have mag ign.--leave your 6 disconnected from starter and jump with 12 and see if it still drags.---I am thinking your starter is worn out like most of my old ones.---Would almost look like time for a new starter.--looks like you did all the tests. thanks; sonny

Well... the starter was rebuilt just over a year ago and it's shiny and clean and new. So I tried your other idea...

I disconnected the 6v battery and pulled out a 12v that had a charge and jumped it. The starter ran so I pulled the choke and tried to get the engine to fire, but it backfired instead. A couple more attempts and the starter stopped. Thought the battery pooped out and so I grabbed my recently purchased 6v and tried to jump it. The starter turned again, but it was definitely a lot slower than the 12v.

[Eugene]

12 volts turns a 6 volt starter quite a bit faster than a 6 volt battery.

Back firing, most likely a faulty ignition timing issue.

[Slim140]

I agree with Eugene, timing needs adjusting. The 6V will turn it over much easier with the timing correct.

[SONNY]

If everything is right 6-v is fine and starts cubs fairly easy but things gotta be fine tuned to do so! thanks; sonny

[Eugene]

Most Cubs can be hand cranked to start the engine. If the engine is in good condition and the ignition timing is up to snuff - - 1, 2, or 3 each 1/3rd revolution of the hand crank and the engine starts.

So, how fast the starter cranks over the engine is immaterial. My 154 Cub Low-boy, starter/generator, very slow engine cranking speed, will only take a revolution or two of the engine to start.

[Matt Kirsch]

Yes, but the engine should crank over decently on 6V.

Frankly, it sounds to me like you've got sketchy connections or cables in the mix somewhere. The last experiment with the 12V battery where it stopped turning, but then worked with the 6V battery, is proof of that.

A 12V battery will crank a Cub engine for a long time, and won't just suddenly "conk out." It'll slow down gradually over time.

Your "conk out" is because one of the connections is iffy and arced. The carbon created by the arc insulated the connection so it was no longer making contact. Reconnecting to the 6V battery made fresh connections so it worked.

Keep in mind that a jumper cable does not have anywhere near as good of a connection as a battery clamp.

Also, cables can be bad internally. If you see any blue or gray powder on the copper, the cables may be corroded right up into the sheathing.

[Eugene]

Does the magneto click, impulse coupling snap, when hand cranking the engine?