850 - no spark

[douglloyd]

Hello,

I brought home an 850 that sat outside for a couple years. PO converted to 12 volt with what looks like 10si alternator. V/R has been removed, but wiring is kinda farmerized.

Anyhow, I'm working on getting it started for the first time in quite a while. Have the carb hooked up to a temporary gas tank with clean 100% gas. Drains through pretty good. Have shined up and replaced battery connections. Starter and solenoid are working fine, and I have 12v to the + post on the coil. No spark though.

Could not read the writing on the coil so I replaced it with a known good 12v ("No resistor required" printed on the side) coil. On the dizzy, I've replaced the points, rotor, cap, and condensor.

I metered the spark plug wires and they all test OK for continuity. Pulled and cleaned plugs, then I installed a copper battery terminal lug at the battery box bolt so I would have a good strong negative ground to test with.

Have been using two separate spark plug test tools, but still cannot get any spark. The I&M manual does not have a lot for ignition troubleshooting. What kind of tests can I run from the coil through the distributor?

thanks,
Doug

 

[WNY Molines]

Doug I think you need to take the wire that goes from the coil to the distributor and put it on the other terminal on the coil to start your troubleshooting. Grab a test light and make sure that you have power to the coil when your key is on.

 

[douglloyd]

(quoted from post at 22:20:34 03/13/16) Doug I think you need to take the wire that goes from the coil to the distributor and put it on the other terminal on the coil to start your troubleshooting. Grab a test light and make sure that you have power to the coil when your key is on.

I do. Key on, I get 12v at the + terminal. I did test that far, but nothing further.

I checked this when I replaced the coil. The feed from ignition is to the + side, just like on the old coil. - side goes to the dizzy.

Only reason they look reversed might be because I rotated the coil so the markings face outwards - easier to read later on.

But thanks for responding though. What kind of test can I run with a meter from the coil downstream through the plugs without frying it or myself?

My bet is on the distributor being the problem. I&M manual does not speak to this.

thanks,
Doug

 

[old]

+ side of the coil should go to the ignition switch and the - side to the insulator on the side of the distributor. Points should be set at 0.025. When the points open you should get a spark form the center wire on the cap. Years ago I would use all that fancy stuff to test for spark but found it can be done with out and takes no brains to do so.
Simple open and close the points with ignition turned on you should both see and hear a spark at the point.
If not spark at the points make sure there clean and do not have a protective coating on them.
If still no spark move the crank so the points are open and remove the + wire off the coil turn on the ignition and touch the wire back on to the coil and of again and watch for a spark. If when the points are open and you have a spark there that says you have a short in the distributor

 

[Ozlander]

(quoted from post at 16:20:34 03/13/16) Doug I think you need to take the wire that goes from the coil to the distributor and put it on the other terminal on the coil to start your troubleshooting. Grab a test light and make sure that you have power to the coil when your key is on.

I agree and you need to change the points as they are now burned up from running 12 volts straight threw them.
It will never start until you get it wired properly.

 

[douglloyd]

thanks Old - that's what I was looking for. It stopped raining, so I will try this out and report back.


Ozlander - the tractor is not wired wrong (yet!) see my reply above. Points are new Eschelin (sp?) Blue Streak with the brown rubbing block.

thanks,
Doug

 

[douglloyd]

Back again.

I used a 12v test light this time.


Ignition on, 12V to the positive post of the coil.

Dizzy cap off, pushed the points open with a wooden dowel. No spark at the points.

Turned off ignition, disconnected ign to coil wire, propped points open, turned ignition back on and touched ignition wire to coil + post. No spark.

Cleaned the new points with paper. With cap off and points open I get 12v at both posts of the coil, the connection at the dizzy, and all the way through to the arm on the points.

What else should I check?

thanks,
Doug

 

[cheif]

Attempting to start my 850 after sitting in an open shed all winter with no success I went through all the usual procedures with no success. Your comment about checking for continuity prompted me to write. I did that and all read ok. Finally in desperation I swapped the coil to dist. cap lead with on old one from the scrap pile and Hurrah!! she fired right up. That was a copper lead and looks fine. I guess my point is when working with high voltage a continuity test is only part of the story. I learned that from many years working with aviation electronics.
I have heard stories from auto mechs. about raising the hood on a rough running auto and see stay voltage running around.Just my two cents worth but we talk about these simple old electrical systems but they can sure be frustrating at time.

 

[old]

Did you get the e-mail I sent you

 

[Tom in TN]

Doug,

Please don't be offended by the simplicity of this post if you are already familiar with what I am going to say.

Let's talk theory for a minute:

1. The primary ignition circuit consists of a battery, ignition switch, primary winding of a coil, points, and a condenser in parallel with the points.

2. One side of the points is connected via wire to - side of the coil, the other side of the points is connected to the base of the distributor via the screws that hold the points in. The base of the distributor is at ground potential by virtue of the fact that the distributor is mounted in the engine. (That's a critical point that we'll talk about more later.)

3. With the ignition switch on (12 volts to the + side of the coil), current will flow through the primary winding when the points are closed. That is to say, + voltage is applied to the coil, if the points are closed, the circuit from the + side of the battery will be completed through the coil, through the closed points, to ground. The coil will be "charged up", that is to say a magnetic field will be created inside the coil.

4. When the points OPEN, the magnetic field in the primary winding of coil will collapse and induce a large voltage into the secondary coil winding (inside the coil). That large voltage in the secondary winding of the coil will be presented to the wire from the top of the coil to the center terminal of the distributor cap for distribution to the spark plugs.

5. The primary purpose of the condenser is to absorb a current discharge that happens when the points open, thus reducing the possibility of allowing an arc to form across the points which would damage them. It is primarily an arc suppression circuit.

Here's the crux of the matter - If I understood you correctly, you have 12 volts on the plus side of the coil. You were able to trace that to the wire that enters your distributor. You could trace it to one side of the points even when the points were closed. That is ABSOLUTELY WRONG. It indicates that you do not have a path to ground through your points. No current is ever flowing through the coil to create a magnetic field inside the coil. Breaking the points with a wooden rod makes no difference because you already have an open circuit on the ground side of the points.

I believe that you do not have a good ground connection from your battery to the frame of your tractor, or you have the points installed so that they can never close, or the points are dirty/corroded so that even if they are touching one another, no contact is actually being made, or there is something wrong inside the distributor so that the distributor plate is not at ground potential.

One final possibility is that the condenser is shorted out, thus causing a path to ground that can never be broken by the points opening. You mentioned that you are checking voltages with a trouble light rather than a volt meter. I suppose that it is possible that the trouble light would glow slightly if the condenser were shorted. A volt meter would clearly show if the condenser is leaking, but maybe the trouble light wouldn't.

This is a long-winded post. You very well may already know everything I've said here, in which case I apologize for wasting your time.

Tom in TN

 

[douglloyd]

No, but your tests worked!

I went back over the tests, then noticed I was not getting voltage through the points when closed. These are new Blue Streak points, but I remembered what you said about dirty contacts.

Did not want to rough these up but cleaning them with paper was not doing the trick. I removed the points and used a small piece of fine steel wool on the contact points. Cleaned this off, reinstalled the points making sure they were set at .25 and tested again.

Now I get the spark you described at the coil post when the points are closed and ignition is on. Next I pulled a spark plug wire and hooked up to one of the plug testers. Not a real hot fat spark, but it's there.

So thanks for the procedure to test with. I know what to do next time.

thanks,
Doug