Johnson 1949 HD 25 No Spark

[Tubs]

When both cylinders won’t produce a spark, everything checks out OK, but you still get nothing, try this. Mark the center of the magnet in the magnet rotor.  On top so you can see it. Rotate the motor till one set of points start to open. Now check to see if the coil that the magnet (your mark) is pointing to – is connected to the points that just opened. If not, at some point, you got the coil wires to the points switched.   

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

1 user thanked author for this post.

aquasonic

[TiIngot]

Thanks Tubs.  My first observation is that I have not completely disassembled the and reassembled the ignition assembly, only taken off one part at a time.  Also, due to the length of the magneto wires and their routing within the ignition plate I don’t think they could be switched and last, the motor was running, then not, before this trouble began 30 years ago when I broke the recoil rope trying to get it going.  I just don’t know if back then it was running on only one cylinder when a second issue developed causing complete failure.

With that being said, I marked the center of the magnet on the magnet rotor as directed and reinstalled it in the keyway.  Rotating the shaft clockwise, when the mark gets to a set of points they are already open and as the mark passes the points they close.

Continuing to rotate the shaft, when the points begin to reopen the magnet mark is pointing to the general side of the magneto going to that set of points that just clothed so I think that is OK.

I’m giving it a break for the week.  I have a new set of condensers coming from eBay.  When they arrive, I’ll install them, reset magneto and points gaps, recheck continuity of all wires and try again.

 

Retired titanium melt shop manager. (Think about me next time you fly in a window seat and look at the engines spinning below the wings!)

[TiIngot]

To all that have responded, it’s New Year’s Eve and I just could not ignore this outboard.  I think the correct term is obsessed.

I disconnected the single ground wire going to the stop switch from each point set and taped them, replaced the flywheel and nut.  I then turned off my workbench light and used my DeWalt drill to spin the motor.  I have spark, but a very very very weak spark in the test light at both plugs.  It is really dim or even intermittent.

Two new condensers are on order.

Retired titanium melt shop manager. (Think about me next time you fly in a window seat and look at the engines spinning below the wings!)

[labrador-guy]

Tilingot  my two cents here goes like this,  the two points wires at the kill switch do not go to ground.  They short to each other to shut off the motor.  Also sometimes a condenser will short out internally causing spark to stop completely.

dale

happy new year!

[JACQUES]

JohnsonParts-HD25

sorry if I am repeating myself but the HD25 magneto is covered in the free downloable Johnson service manual

https://www.socalaomci.com/library/johnson_service_manual_10th_edition.pdf

pages 22-28

download  store on a PC  or print locally double sided  bind with a spring cord with plastic cover sheets front and back

You can even split the file in 2  books for easy reading   or just print  off what you need .

 

Joining AOMCI has priviledges 🙂

[TiIngot]

I already have downloaded the service manual and printed off the necessary pages.  I found on eBay a complete magneto plate assembly that includes points, magneto condensers flywheel etc. for $14 and waiting for it to arrive before continuing diagnostics. It has the stop switch on it also so I can check its continuity with mine when it comes and compare the two and the capacity readings of the condensers with mine too.

I used my grandson as a guinea pig.  He held the spark plug wire while I turned the magneto with my drill.  No spark showed in the plug test light, but he felt a couple real light tingles in his fingers on one cylinder.

Referencing a comment about the single condenser wires not going to ground but go to each other.  Still confused here and maybe I mis-stated myself.  The two single wires go to an insulated nut on top of the stop switch bolt assembly.  I believe when the magneto is moved to the stop position it contacts the bottom of the stop switch bolt and thus grounds the capacitors to stop the outboard.  However, on mine there appears to be an insulator on the bolt that separates one condenser wire from the other and only one condenser gets grounded when in the stop position.   I don’t want to mess with the ground switch until I have the second magneto plate in hand because I cannot find a good diagram of the insulators within the assembly.

The other problem is eBay, on another item.  I found two OEM 300153 condensers and placed an order from someone named: marinepartswarehouseky.  Two condensers ordered Dec.30.  Confirmation email received Dec 30 also with invoice and eBay order number.  Dec 31 full payment was pulled from my charge card.  However, in eBay the order for the condensers does not appear on my account, entering the order number comes up ‘Order not found” and the seller has not answered my messages for two days now.

 

The saga continues.  I got all winter.

Retired titanium melt shop manager. (Think about me next time you fly in a window seat and look at the engines spinning below the wings!)

[JACQUES]

I believe when the magneto is moved to the stop position it contacts the bottom of the stop switch bolt and thus grounds the capacitors to stop the outboard ….   

 

no HD expert but the condenser basically serves to  prevent excessive sparking across the points when it/they opens.  The collapsing magnetic field created  in the primary winding by open points   causes a counter rise of voltage  as the coil tries to sustain  the magnetic field  .  This counter EMF tries to jump across the point (s) which eventually burns  their surfaces but the condensers absorb  this kickback sparking.

The proximity of collapsing  primary coil’s current induces   the  secondary coil’s high voltage   which  reaches the  sparkplug (s) s and  tries to establish a ground  path by jumping the .020 gap.

sometimes the “plug body” grounded in the threads is the initial point of entry of the returning voltage but said voltage must have continuity back to the coil body otherwiseit may try to jump anywhere it can  (watching it  in operation in the complete darkness can pinpoint some  “extra” jumping site wherreas all 100% of the spike needs to jump the plug gap.

Some engine actually have a ground wire connecting the mag plate body  to the engine body to facilitate this.

MR. Mohat article  on the “Magic of magneto”  is a much better read !

if your ” guinea pig” only felt a week jolt well it is weak and weakness may come   from a weak magnetic field induced by weak magnets

have you tried just holding a screw driver near the magnet (s) to see if they pull strongly ?  are the coil laminates adjusted close to them

have you  tested the ohms values on  boot to primary wires (post results)

 

Joining AOMCI has priviledges 🙂

[JACQUES]

chat gpt info

How the STOP button works on an HD25 outboard (older ignition)

On an HD25 outboard, the STOP button is a kill switch.<br data-start=”301″ data-end=”304″ />Its only job is to shut the engine off by killing the spark.

Basic principle

• The engine has a magneto / ignition coil that generates spark for the spark plugs.

• One wire from the ignition system is the kill (stop) wire.

• Pressing the STOP button connects that wire directly to engine ground.

• When the ignition is grounded, the coil cannot produce spark.

• No spark → engine stops immediately.

What happens electrically

• STOP button released (normal running)<br data-start=”802″ data-end=”805″ />Kill wire is open (not grounded) → ignition works → engine runs.

• STOP button pressed<br data-start=”901″ data-end=”904″ />Kill wire is grounded to the block → ignition shorted → engine stops.

Why this system was used

• You cannot “turn off” a magneto ignition like a battery system

• The only reliable way to stop the engine is to short the ignition to ground

• Simple, rugged, and works even with no battery

Components involved

• STOP button (momentary switch)

• Kill/stop wire from ignition coil

• Engine block ground

• Magneto / ignition coil

Safety lanyard (if fitted)

• The safety clip does the same thing as the STOP button

• Removing the clip grounds the ignition

• Stops the engine if the operator falls or leaves the helm

Common faults

• Engine won’t stop<br data-start=”1598″ data-end=”1601″ />→ broken kill wire, poor ground, or dirty stop switch

• Engine won’t start<br data-start=”1681″ data-end=”1684″ />→ stop button stuck closed or kill wire shorted to ground

• Corrosion inside the button is very common on older motors

Simple test (engine off)

1. Disconnect the kill wire from the ignition

2. Use a multimeter:

   • Button not pressed → open circuit

   • Button pressed → continuity to ground

⚠️ Do not leave the kill wire disconnected during operation — you lose emergency shutdown.

Joining AOMCI has priviledges 🙂

[JACQUES]

more chat stuff

(engine cranks but will not fire)

Step 1: Eliminate the STOP circuit

This is the most common cause.

1. Locate the kill (stop) wire coming from the ignition coil/magneto

2. Disconnect it completely from the stop button / harness

3. Crank the engine

Result

• ✅ Spark returns → problem is STOP button, wiring, or ground

• ❌ Still no spark → ignition fault further inside

If spark returns here, skip to Part C (No-Stop diagnosis)

<hr data-start=”834″ data-end=”837″ />

Step 2: Check for spark properly

• Install spark plug into cap

• Ground plug body firmly to engine block

• Crank engine

You want a strong blue snap, not weak yellow.

<hr data-start=”1015″ data-end=”1018″ />

Step 3: Inspect ignition coil

• Look for:

  • Cracked case

  • Oil leakage

  • Burnt smell

• Measure resistance (typical older coils):

  • Primary: ~0.2–1.5 Ω

  • Secondary: ~3k–10k Ω (without plug cap)

If open or shorted → bad coil

<hr data-start=”1271″ data-end=”1274″ />

Step 4: Check points (if equipped)

Many HD25-era motors still used breaker points.

• Remove flywheel

• Inspect points:

  • Clean, flat, not burnt

  • Opening and closing when cranked

• Clean lightly with paper or points file

• Set gap (typical): 0.018–0.022 in

Dirty or oxidized points = no spark

<hr data-start=”1588″ data-end=”1591″ />

Step 5: Condenser (capacitor)

• A failed condenser causes:

  • Weak or no spark

  • Heavy arcing at points

• No reliable meter test — substitute with known good unit

<hr data-start=”1764″ data-end=”1767″ />

Step 6: Flywheel magnets

• Magnets should be strong

• Hold a wrench near magnet:

  • Weak pull = weak spark

• Rust or oil contamination reduces output

<hr data-start=”1929″ data-end=”1932″ />

PART B — SPARK PRESENT BUT ENGINE WON’T RUN

(briefly included for completeness)

• Fouled spark plugs

• Incorrect plug gap (usually 0.025–0.030 in)

• Incorrect timing (points cam slipped)

• Sheared flywheel key

<hr data-start=”2152″ data-end=”2155″ />

PART C — NO-STOP DIAGNOSIS

(engine runs but will not shut off)

Step 1: Test STOP button

• Engine off

• Multimeter on continuity

Button	Expected
Not pressed	Open circuit
Pressed	Continuity to ground

❌ No continuity when pressed → bad button

<hr data-start=”2450″ data-end=”2453″ />

Step 2: Check kill wire

• Look for:

  • Broken strands

  • Corrosion

  • Loose terminal

• Verify wire actually reaches engine ground when button pressed

<hr data-start=”2617″ data-end=”2620″ />

Step 3: Ground path

Old outboards depend on metal-to-metal grounding.

• Clean:

  • Button mounting surface

  • Engine block contact points

• Paint and corrosion can prevent grounding

<hr data-start=”2815″ data-end=”2818″ />

Step 4: Direct ground test (definitive)

With engine running at idle:

• Momentarily touch kill wire directly to engine block

Result

• Engine stops → STOP circuit faulty

• Engine keeps running → ignition coil not ground-killable (rare but possible)

<hr data-start=”3089″ data-end=”3092″ />

QUICK FAULT SUMMARY

Symptom	Likely Cause
No spark, won’t start	Kill wire shorted
Spark returns when kill wire removed	Bad stop switch
Weak spark	Points or condenser
Runs but won’t stop	Broken ground
Stops only at high RPM	Marginal coil or weak magnet

Joining AOMCI has priviledges 🙂

[TiIngot]

Thank you for this information but this old 1949 has, what I believe, a very simplistic engine stop system and I don’t think it is my primary problem.  It’s just a secondary issue after I solve the no spark issue.

There is no modern stop button, switch, lanyard etc.  There are three wires coming off the points.  Two wires, one from magneto and one to condenser on one side and a third wire going from the points to the stop switch (It is actually an insulated bolt, meaning it is not grounded when outboard is running).

HD 25 outboard speed is controlled by a horizontal lever that moves left to right on the front of the outboard.  The lever performs three functions.  It advances and retards the magneto, controls the carburetor fuel output and moving the lever to the far-left position to “STOP” grounds the stop switch bolt.

I have disconnected the wires from the stop switch and taped the ends to isolate it from the magneto circuit.

I knew nothing about outboards until I started this project two weeks ago and have learned everything from this group.  It takes time when it is your first adventure, a lot of wheel spinning and head scratching.

Monday 16Jan26 my eBay parts arrive, and I will again be at my workbench.  Updates will come after then as I proceed.

Retired titanium melt shop manager. (Think about me next time you fly in a window seat and look at the engines spinning below the wings!)

[Author]

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