Ignition troubleshooting

Hello,

I have an MF-50 that's not getting spark, and I'm stumped as to why. The coil puts out nothing to the distributor cap, and a new coil has not solved the problem. I've tried a few troubleshooting methods and found out that there are 12v going in to the coil when the ignition switch is on, but test light indicates that the current is totally lost while cranking. I've tried jumping the ignition switch and the starter button in case they were bad, but current is still lost.

I don't know much about ignition systems... basically I've learned everything I know in the last couple days looking online for troubleshootng. But it seems to me as though the points close in order to complete the ground on the coil to make the coil put out current to the distributor cap. If that's true, the points not making contact would mean the coil is not grounded, preventing it from putting out any current. Unless it's a condenser problem, or both. Any ideas?

Thanks for your time!

If you are suggesting that the 12v TO the coil goes away while cranking, I would suggest you try to determine if your tractor uses a starter bypass circuit. This is intended to supply a full 12v to the coil while cranking then once started switches to a resisted voltage to the coil once started, approx 5v. If the starter bypass circuit is disconnected or faulty you will loose all voltage to the coil while cranking.
Also are you saying you jumped the ignition switch by supplying voltage to the coil positive directly? If so this would eliminate my prior suggestion. If not, try that. That is, supply power directly to the coil positive terminal.
You may also want to try to rotate the engine by hand while observing the test light with it connected to the coil negative. It should come on then off as the engine rotates. It does ground the coil primary winding as you suggested.

The ignition works by the points closing the circuit in the ignition primary circuit and casing currentot flow in the coil primary winding, genrayting a magnetic field about the primary winding. When the points open, the primary current stops and the magnetic field in the primary collapse and induces a high voltage and current in the secondary winding of the coil. That high voltage generates the spark as it jumps the gap on the plug. That"s the theory.

So you need to havea good ground at the distributor which means you battery ground must be making good contact with the chasis. The primary circuit must have continuity from the battery to through the key switch or the solenoid , through to the coil and through to the distributor side of the primary. The distributor muust be well grounded and the points mst be free of oil and corrosion and be properly set.

An easy way to check for spark is to pull the center wire from the distributor cap and hold it neat a good ground. Try a start. You should have a FAT, BLUISH-WITE SPARK, the color of lightning.

Take a jumper from the battery directly to the battery side of the coil and try a start. If you get a spark, then your problem is in the circuit between the battery and the coil. You say you have bypassed the the starter button and the ignition switch but you need to bypass the solenoid if you have one.

If you don"t get the requisite spark, I would start by checking the points. make sure they aren"t corroded or burned. Take a piece of brown paper bag and drag it through the closed points to clean off any oil or film. Make sure the point gap is per spec.
A grounded test light held on the distributor side of the coil should alternately show on (points open 12 V to ground) and off (points closed ground to ground).
The condensor being bad would cause a weak spark. No good way to check for a bad condensor so just replace it.

Look in the cap and make sure that the top of the rotor is contacting the carbon button on the top of the cap and make sure the rotor is indexed to the slot in the distributor shaft. Check the side play on the distributor shaft by pushing radially(from the side) on the shaft with the points closed. Watch the points when you do this to see if the points move. They should not. If they do your shaft and/or bushing are worn.

Systematically make these checks and record what you find and get back here if you still are having problems.

Don't just jump the switch, run a wire (with alligator clips) from the pos. of the battery to the pos. terminal of your coil.

Thanks for the info, guys.

We tried connecting the wire from the battery to the coil, still no spark.

We re-checked the power going to the solenoid, and it kept going down to about 5v while it was cranking. Then, it was sporadically getting the 12v and not getting the 12v just with the key on and no cranking. We've also been having a hard time getting the starter to work. It seemed as though the key switch was extremely sensitive and had to be in JUST the right position to provide power to the starter button, and to get 12v at the coil.

Today, we thought the ring terminal at the switch end of the coil wire was corroded, so we replaced it and it seemed to supply a consistent 12v shutting the switch on and off and tapping it. Then we screwed the switch back in and lost it. Now I'm thinking the switch is the issue, and in taking a closer look at that, I made this thread:

http://ytforums.ytmag.com/viewtopic.php?p=4899410#4899410

Once I verify that the wiring is actually correct and know what type of switch to get and have it installed, I'll see if we'll get a reliable 12v. If so, we have new points, condenser, rotor, and spark plugs to install when it's not 22 degrees out. No shed, garage, shop, or other shelter to work from, unfortunately.

After doing some rewiring to match this diagram:

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=mf&th=92333%3E

And replacing the points and condenser, and after battling with the ignition switch to get it to make contact, we got spark! My dad said the points looked tolerable when we took them off, but we replaced them anyway, along with the condenser, which was probably the culprit.

It took a little bit of cranking, but eventually ran on full throttle and sputtered and died when we took the throttle off. Adjusted the timing and it runs beautifully, much better than it did when we last ran it. It doesn't need to warm up for half an hour before it can move anywhere... in fact, it'll even get itself going in top gear easily. I think it definitely benefited from the new points whether or not they were "the" cause. We should have done this in the beginning, but we didn't have the parts available so we got hung up on everything else.

Thanks for the words of wisdom, everyone -- I'll definitely refer back to them if it goes down again!