pony motor back fires

Anonymous-0

Well-known Member
Recently bought a 720 Diesel pony motor back fires when running does not sound up to full speed. could not get it to start until I cleaned points. It does not have enough power to start diesel motor. tractor does run when pull started. Is it ignition, carb, or valves need set. Thanks for help.
 
"Is it ignition, carb, or valves need set."

Could be all three.

First off, each of the two (fragile) coils fires two cylinders, with the help of two sets up breaker points.

Only when you are sure all that is in order is there any use moving on to the carb and valves.
 

1-800-522-7448 for the operators and service manuals . The parts manual is on the JD web site.
If somebody thought they were adjusting the idle or main jets with a slot screw driver. They may have twisted off the fuel transfer tube.
As previously stated ignition is suspect . Properly gapped Autolite 437 plugs.
There are two different types of coil connections and two different types of plug wires. Mix them and she won't run decent. Did somebody cross the wires ?
 
Most likely it is ignition trouble. It's kinda hard to get the wires crossed up, the front coil sparks both front plugs & the rear coil (and rear points) sparks the rear two plugs.

Between the ignition resitor, the main ignition switch, the bypass switch & all they can get a bit bewindering. Remeber the front plugs are in a loop meaning they're in series with each other. Same with the rears.

Since yours starts but won't cut the mustard, It's likely a bad coil or condenser or both or the ignition resistor on the back of the main switch.

The resistor on the back of the ignition switch can cause exactly what you describe! There are two ressitors on that switch. One big one for the dim lights and a little one for the cranking engine ignition. If that resistor wire (very reluctant to corrode because of the alloys it's made of) looses good contact with the switch lugs which rust, resistance goes up, spark intensity goes WAY down & they may start but run poorly, seem to miss badly but playing with the choke can sometimes get it going causing one to think it's all a fuel problem!

Also, even though it may be running on two cylinders or one coil because the other coil is completely toast, that does NOT mean the one it's running on is good! Been there found it out the hard way. Kinda like the 24 volt starting systems.... Don't just replace one battery. Buy two! Reason is if one is so bad it doesn't work at all the other is likely just about as bad but just barely good enough to work sorta. If it comes to being a bad coil, just bite the bullet & get an entire kit. Cheaper in the long run.

Maybe that helps?
 
If I'm not mistaken I think some of the gents when they replaced the Pony coils with the later modern replacement units did away with (by passed) the on switch ballast and never had any problems. Any thoughts on that??

John T
 
Have seen the same comments, wondered the same thing! Have also wondered if they're just on line so short a time the duty cycle is not insanely abused and maybe modern magnet wire has better resistance to heating so they just live through the abuse?

I bought mine somewhere near 15+ years ago & to this day I don't know if they were more like the originals or if they're newer higher voltage windings.

I'm sure B&D would tell me to buy a shop manual but though I have Mr. Deere's manual (since 1982), I've never found where an expected measured resistance and/or current through is listed. At $55 plus change per coil (then a third of mother Deere's price) I was not in the "let's experiment" mode! I installed 'em WITH the original resistor in place.

It was a new machine!

Year before last the cranking engine suddenly became VERY cantankerous. Naturally at a show! He would try and try to start but stalled, sputtered, fired out the exhaust & became quite a general pain. Given it had an 11 year old battery in it I didn't tinker too much knowing a dead battery could soon be added to the list of problems! I elected to let it sit as it was time to call the day anyhow. Next morning (nobody watching) it started right up! GRRRRRR! Loaded him up to go HOME, did not pass go, did not collect $200!

When I got to hunting for what was going on, it occurred to me it tried to start but... only with the starter engaged! Light bulb lit saying "ya dope, it's wrokin on the bypass circuit"! Checked closed points, switch on voltage at the distributor input lug. Only 2 volts! Seemed maybe a tad bit low!

After reinstalling the resistor wire with the lugs cleaned all shiny using new screws, new star washers and slathered with never sieze, it sticks in my mind voltage was around 4.1 or maybe 4.5?

He pops right off & doesn't smoke near so badly, tunes leaner & will crank with the valves closed 'till the tank runs dry!

I asked a feller who sells them about using the resistor or not. All I ever got was a bunch of stammering and hmmmm hawing. Began to seem like he didn't know a coulomb from a columbine!

Doubting these coils have gotten cheaper through the years, I'm reluctant to remove the resistor feeding them with battery voltage full time to find the hard way that it's a bad idea!

Burning up or loosing a couple $20's now & then is one thing but when their pal Mr Franklin goes along for the ride... that's another matter! 'Specially when it tunes & runs right sweetly as is!

Without sacrificing one to determine the primary's wire gauge and/or counting the ampere turns & calculating what is needed to saturate the core... the short answer is... Beats the Wampum outta me! The way it is, it works well & so if it ain't broke she don't need fixed!

Thanks fer askin!
 

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