no spark on 704...need help

[Sailman 1,291]

I have this old 704 that I resurrected from the "dustbin of history"...so to speak.

Got the engine freed up (had a stuck exhaust valve) and all the rest of the engine looked good (piston, cylinder walls). Its a K161 but pistons were smaller so I guess its actually a K141. It is a recoil start so I think that makes it a magneto ignition. Heres my issue;

There is a switch at the console. When I first got the engine back together with the switch in the on position I could get spark at the plug. With switch off - no spark. I could get it to try to run with gas spray in the carb but would not keep running.

I took the carb off for a deeper cleaning (3 more cycles in the ultrasonic cleaner).

When I went back to the engine now I get no spark at the plug with switch on...???

Trying to diagnose what to do. I have the wire that goes from the switch and then behind the bearing plate. Another wire coming from the bearing plate to the points. I understand the condenser is behind the bearing plate too. The spark plug wire also comes from behind the bearing plate.

I checked continuity from the switch to the points and have continuity with the switch in the on and off position. Is that right??

Can someone please explain to me how all this ignition works on a K-161 recoil start?? I am lost. Nothing in the service manuals helps me get this.

Norman at "I save tractors" says to use condenser external (not replace old one under bearing plate). How would that actually hook up with the wire to the switch?

Just for kicks I disconnected the wire from bearing plate to the points and hooked a new condenser to the points. Still no spark turning engine over...same thing with both wires attached to the points.

Am I going to have to pull flywheel and bearing plate?   Really need some advice here. Thanks!!

Edited July 6 by Sailman

[Keaton 435]

@Sailman im not the best at this, but first off I would take your points off and file them with a fingernail file and do you have a feeler gauge, some way, set them at 20 tho, and if that does not work I would pop the flywheel off and see if the coil is clean and if the magnet is clean. rust free, if not sand a bit with some finer sand paper, but before you do any of this I would steal a plug out of another mechine and make Shure the plug is good, I have had that happen before. and make Shure you have a good ground or apart tester, if none of that works, I would un Hook the switch and put the end of the ground wire on and off the frame to cross out the kill swich. that would be my suggestion, or that is what I would do in a order if that makes any sense, good luck

1 different plug

2 test kill swich

3 clean and set points

4 take flywheel off and sand coil and magnets

[squonk 41,104]

Remove the wire at the switch. Then check for continuity at the wire to ground. You do not want that. That is how you shut the engine off. By grounding the mag coil. Perhaps a mouse got in there and chewed some insulation off of the wire or water/ dirt got into the switch.

[953 nut 55,224]

10 hours ago, Sailman said:

Norman at "I save tractors" says to use condenser external (not replace old one under bearing plate). How would that actually hook up with the wire to the switch

Not quite correct. When capacitors are placed in parallel the capacitance of each is added together putting it high, out of the desired range. If the old condenser has shored out putting a new one parallel to it won't change a thing.

The unit of measure for a condenser is the Farad. Many electronic components like radios and TVs use capacitors that are in the microfarad range (ten to the minus six power Farads) and our small engines use a condenser that is in the nanofarad range (ten to the minus ninth power Farads) which is based on the voltage range they work in. A magneto ignition system uses a 100 to 250 nF condenser

The coil and capacitor (Condenser) live behind the flywheel mounted to the bearing plate. Though one of these may be the problem I would start on the outside before pulling the flywheel. The majority of problems are a matter of a wire being accidently shorted out to ground preventing the magneto from producing spark.

I too would begin with a known good spark plug as @Keaton suggested, if spark returns you have to go no further, but cleaning the points would be a good thing too.

As Mike @squonk suggested you can disconnect the wire to the switch but also disconnect the wire going to the points, this will remove all external grounds from the primary winding of the coil.. Check the insulation on both wires where they enter the engine. Now turn the engine over and see if you have spark at the plug. A magneto will produce spark at the plug without the points connected, the points setting adjusts the timing of the spark. If you have no spark it is time to remove the flywheel, however if there is spark then connect the wire to your points (you already cleaned and adjusted them before). Now turn the engine over to verify spark is present. 

If there was no spark with all external grounds removed then I would suspect the condenser has failed, the replacement (Kohler 235786) can be mounted on the outside of the engine and the lead wire connected to the points and the old one removed completely.

[rmaynard 15,458]

Here is a thread that I started on basically the same problem.

 

https://www.wheelhorseforum.com/topic/98625-704k161t-wont-start/#comment-1063231

 

Go to post #13 for my solution to my problem 

Edited July 6 by rmaynard

[Sailman 1,291]

Thanks for all the suggestions.

Update; I disconnected the wire to the switch, installed new points and I am getting continuity between the points and the ground with both points closed AND points open. That should not be correct right?

I disconnect the wire at the points (coming from the bearing plate) and insert a new condenser and still no spark, probably because I am now getting nothing from the magneto, right? In this configuration I get continuity to ground only with the points closed, not open.

This would be normal right?

Sounds like time to pull the flywheel and see whats happening at magneto and coil?

Am I right to assume something is grounding out the points?

I do have a new plug installed but me thinks its the grounded wire issue.

 

[Sailman 1,291]

6 hours ago, squonk said:

Remove the wire at the switch. Then check for continuity at the wire to ground. You do not want that. That is how you shut the engine off. By grounding the mag coil. Perhaps a mouse got in there and chewed some insulation off of the wire or water/ dirt got into the switch.

 

 Just to clarify...this IS what I have happening. Wire, disconnected from the switch HAS continuity with the ground. Pull the fly wheel and see? I guess I could replace the condenser while in there?

[squonk 41,104]

Follow that wire all the way under the flywheel and look for a chafed wire like Bob found on his.

[953 nut 55,224]

The resistance of the secondary should be around 8k to 10k ohms. The resistance of the primary should be around 1.0 ohm. You need a good digital meter to tell the difference between a shorted primary and a good primary. If it really is shorted (unlikely) check the wiring harness where it enters the stator plate and under the clamp for a pinched or bare wire.

Both the primary and secondary coils surround an iron core and are grounded through the core to the stator plate. While the points are closed the rotating flywheel magnets induce a voltage and current flow through the primary coil which is made up of a few hundred turns of heavy wire. This current flow creates a magnetic field. When the points open the current flow stops and the field collapses through the secondary coil which is made up of thousands of turns of fine wire. This collapsing magnetic field creates a very high voltage in the secondary due to transformer action and the high voltage arcs across the electrodes in the spark plug.

The resistance of the primary is measured between ground (engine, or stator plate if the stator is dismounted) and the wire from the points and condenser. Resistance of the secondary is measured between ground and the spark plug connector at the end of the plug wire

[Sailman 1,291]

@953 nut does it matter if the points are open or closed when measuring resistance at the primary and secondary?

Will pull the flywheel next week and see what I have got. Hoping for a bare spot in the wiring....

Strange thing is, nothing changed on the motor from the time I was getting spark to not getting spark. Just removed the carb. It sat, no movement, in a dry, clean, no rodent shop area....

Edited July 7 by Sailman

[953 nut 55,224]

You will get the most accurate reading with the magneto coil disconnected from anything else.

[rmaynard 15,458]

FYI, if the coil is bad, I have a good one.

 

$75 plus shipping.

[Sailman 1,291]

Here is an update. Problem NOT solved. Here's what I have done;

1. "removed all wires from the condenser, put tape on the ends, put the flywheel back on to see if I have spark". NO SPARK. I also took the red insulated wire from the coil OFF and just left wire to switch and wire to points attached to condenser and did a continuity test. NO continuity to ground. Checked chafe on all wires and all are good. This should mean NO SHORT in wires.

Add the coil red wire and I get continuity with ground with points open and closed.

2. Used my multi meter to check resistance. Set at 20K I get 9.22 - 9.25 on secondary.

Set at 200 I get .6 - .7 on the primary.

This is outside my wheel house so....what does it mean so far? Whats next to try to solve this problem? Any way to test condenser?

Thanks in advance.

[953 nut 55,224]

1 hour ago, Sailman said:

Any way to test condenser?       This video is a good one on condensers, also have one on the  magneto coil. for you to look at.

 

This may help you test the coil.

 

[Sailman 1,291]

I have gone through every possible link in the K-161 I have. Wires are not grounded, installed new points and new condenser so only other option must be magneto. I get a constant ground at the points and condenser connections.

I do get an erratic small spark occasionally after installing new condenser, not once every revolution of the flywheel.

Sound like magneto grounding out?

[squonk 41,104]

Kohler points are driven by the camshaft so spark should occur every other revolution.

[Sailman 1,291]

3 hours ago, squonk said:

Kohler points are driven by the camshaft so spark should occur every other revolution.

 Seems like I can go more than 2 revolutions without any spark. Very erratic. Bad Magneto?

[squonk 41,104]

10 minutes ago, Sailman said:

 Seems like I can go more than 2 revolutions without any spark. Very erratic. Bad Magneto?

Sounds like it.

[953 nut 55,224]

On 7/7/2024 at 8:01 AM, rmaynard said:

FYI, if the coil is bad, I have a good one.

 

$75 plus shipping.

Sounds like you and Bob need to make a deal.