You’re out on the water, the sun is just starting to peak over the glass-calm surface, and you turn the key on that old 1975 Johnson 70 or 75 HP Stinger. Nothing. Just the rhythmic, heartbreaking sound of a starter motor spinning against a cold engine that refuses to fire. You know the drill. You push the key in to engage the solenoid, expecting that satisfying click of the butterfly valves closing, but it stays silent. Honestly, the 75 Johnson electric choke system is one of those beautifully simple designs that becomes a total nightmare the second a single wire gets brittle or a plunger gets sticky.
It’s frustrating.
Most people think these old outboards are bulletproof, and they mostly are, but the ignition and enrichment circuits on mid-70s OMC (Outboard Marine Corporation) engines have their quirks. Back in '75, Johnson was transitioning. We weren't quite into the era of the "Primer Solenoid" that injects raw fuel; we were still dealing with a true mechanical choke plate operated by an electromagnetic solenoid. If that 75 Johnson electric choke isn't pulling the plates shut, you’re basically just draining your battery for fun.
Why Your Electric Choke Is Probably Ghosting You
The system relies on a basic electromagnetic principle. When you push that ignition key in, you’re sending 12 volts back to a small black cylinder mounted near the carburetors. That cylinder—the solenoid—creates a magnetic field that pulls a metal plunger down. This plunger is connected to a linkage that snaps the choke butterflies shut. Simple, right? But after fifty years in a damp, vibrating environment, things go sideways.
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Corrosion is the main villain here. I've seen countless motors where the ground wire attached to the solenoid bracket has turned into a green, crusty mess. If there’s no ground, there’s no circuit. You can push that key until your thumb turns blue, but that solenoid won't budge. Sometimes it’s even simpler: the linkage is just gummed up with old, varnished 2-stroke oil. It’s like trying to move a stick through cold molasses.
The "Click" Test
Before you go buying parts, you need to listen. Turn the battery switch on. Don't crank the engine. Just push the key in. Do you hear a sharp, metallic clack? If you do, your electrical side is likely fine, and your problem is mechanical—maybe the linkage is bent or the butterflies are stuck. If you hear silence, you’ve got an electrical ghost.
I once spent three hours chasing a "dead" choke on a 75 HP Hustler only to find out the purple/white wire had rubbed raw against the block. Every time the owner hit the choke, it was shorting out before it ever reached the solenoid. It’s those little things that kill your Saturday morning.
Testing the Solenoid Without Losing Your Mind
If you aren't hearing that click, grab a multimeter. Or, if you’re stuck at the boat ramp, a simple test light will do. You’re looking for 12 volts at the solenoid terminal when the key is pushed.
- Connect your lead to the wire terminal on the solenoid.
- Have a buddy (or a very long arm) push the key in.
- Check for juice.
If you have power but no movement, the solenoid coil is likely fried. These things get hot. If someone holds the choke in for too long while trying to clear a flood, the internal windings can melt. It happens more than you'd think. On the 1975 models, the solenoid (often part number 0386414 or similar depending on the specific sub-model) is a stout little unit, but it’s not invincible.
What about the manual override?
People forget this exists. Almost every 75 Johnson electric choke setup has a manual lever. It’s usually a little red or black plastic knob on the side of the air box or the solenoid itself. If your electrics fail, you can flip that lever to manually force the choke shut. It’s a lifesaver. If the engine starts with the manual lever but not the key, you know for a fact your problem is in the wiring or the solenoid itself.
Wiring Gremlins and the Ignition Switch
Sometimes the issue isn't at the engine at all. The ignition switches on these old OMC control boxes are notorious for wearing out. The "Push-to-Choke" feature is a physical contact inside the switch. Over decades, that contact gets pitted and charred.
You might find that you have 12 volts at the dash, but by the time the signal travels ten feet down the wiring harness to the motor, it’s dropped to 6 or 7 volts. That’s not enough to pull that heavy magnetic plunger. You’ll get a weak buzz or a "lazy" choke that doesn't quite close the plates all the way.
The Bypass Trick
To verify this, take a jumper wire directly from the positive terminal on the starter solenoid (the big post) and touch it to the small terminal on the choke solenoid. If it snaps shut with authority, your solenoid is perfect, and your wiring harness or ignition switch is the culprit. Honestly, I’ve seen guys just rig up a momentary push-button on the dash because they didn't want to shell out $80 for a new OMC ignition switch. It’s not "factory correct," but it gets you fishing.
Cleaning and Maintenance (The "Free" Fix)
Before you go on eBay and hunt for a vintage replacement, try cleaning the plunger. Take the solenoid off. It’s usually just a couple of bolts. Carefully pull the plunger out—watch out for the spring! If that plunger is coated in a sticky film, clean it with some carb cleaner or brake parts cleaner until it’s shiny.
Do NOT grease it.
Grease is a magnet for dust and salt spray. In a marine environment, grease eventually turns into sandpaper. You want that plunger dry and smooth, or maybe a very light spray of a "dry" lubricant like PTFE. While you're there, check the choke plates in the carburetors. They should move freely with the flick of a finger. If they're binding, your solenoid doesn't stand a chance.
The Gasket and Heat Issue
The 1975 75HP models are three-cylinder beasts. They generate a decent amount of heat under that cowl. If your engine is running hot, it can actually cause the solenoid housing to expand slightly, which might bind the plunger. If you find your choke works fine when the engine is cold but fails after you’ve been running for twenty minutes, check your cooling system. You might have a water pump impeller on its last legs, and the escalating under-cowl temp is messing with your electronics.
Modern Replacements for 1975 Parts
Finding original parts for a fifty-year-old motor is getting harder. You might find "New Old Stock" (NOS) parts, but they often command a premium. The good news is that the basic OMC solenoid design stayed similar for years.
However, be careful.
Some later models moved to the "primer" style which looks totally different. You need the "puller" type. If you’re looking at a parts diagram, ensure you’re looking at the 75HP 3-cylinder assembly. The 75 was a bit of a high-performance trim back then, often found on the Stinger models with the short shafts. They used the same choke setup as the 70HP of the same era, so those parts are usually interchangeable.
Real-World Specifics:
- Voltage Requirement: Needs a solid 12.6V to operate under load.
- Resistance: A healthy solenoid should show very low ohms (usually between 2 and 5 ohms). If it’s "Open" (infinite ohms), the coil is broken inside.
- The Ground Path: The solenoid grounds through its mounting bracket to the engine block. If you painted your engine recently, you might have accidentally insulated the solenoid from the ground. Scrape a little paint away where the bolt meets the bracket.
Troubleshooting Summary Table (The Mental Checklist)
- Symptom: No click, no movement.
- Likely Cause: Blown fuse (check the 20A inline fuse near the starter), dead ignition switch, or broken ground.
- Symptom: Weak click, plates don't close.
- Likely Cause: Low battery voltage, corroded terminals, or gummed-up linkage.
- Symptom: Solenoid works, but engine won't start.
- Likely Cause: Fuel isn't reaching the cylinders. The choke only works if there's gas in the bowls. Check your primer bulb.
- Symptom: Choke stays on (stuck).
- Likely Cause: Return spring is broken or the manual lever is flipped to the "On" position.
Actionable Steps to Get Back on the Water
If you’re currently staring at a non-responsive 75 Johnson electric choke, stop guessing and follow this sequence.
First, verify the battery. These old CDI (Capacitor Discharge Ignition) systems are picky about voltage. A battery that has enough juice to spin the starter might not have enough "overhead" to pull the choke solenoid simultaneously. Charge it fully.
Next, perform a bypass test. Use a jumper wire from the battery positive to the choke solenoid post. If it clicks, your problem is "upstream" in the harness or switch. If it doesn't, check the ground. Take a jumper wire from the battery negative to the metal body of the solenoid. Try again. If it works now, your mounting bracket isn't grounding to the block.
Clean the linkage. Use a toothbrush and some solvent to scrub the pivot points on the carburetors. These are often neglected and get coated in salt or old oil. A drop of light machine oil on the pivot pins—not the solenoid plunger—can make a world of difference.
Lastly, if the solenoid is truly dead, don't just buy the first one you see on a discount site. Check the plunger length and the mounting hole orientation. OMC made several versions that look identical but have different "throw" lengths.
Get that choke snapping shut tight. It's the difference between a day spent fishing and a day spent swearing at a piece of aluminum in your driveway. Properly maintained, that 1975 Johnson will fire up on the second or third revolution, every single time.