1997 Johnson 50 no power after stop/restart

[webbd]

This one has me stumped.

My engine seems to run normally on the driveway, and it seems to run normally for at least a period of time on the water, but after I stop it and restart, it becomes difficult to start, won't idle well, and it will die if I put it in gear.

I'd appreciate any advice on this. I'm sure it's something simple that once fixed, will resolve the issue entirely.

It's a 22 year-old Johnson 50HP with the light-duty housing and VRO still installed and working. I replaced the ignition module 9 years ago to try to address an issue with rough running off-idle. Other than plugs, tuning, impellers, and other basic maintenance, the engine is original. I added an external water-separating fuel filter about 8 years ago due to an issue with bad gas.

This boat is kept in my garage, and is normally used on salt water for island hopping and fishing in the Gulf of Mexico, and every outing included a thorough cooling system flush, hose-down, and dry-out afterwards to limit corrosion. This year, I've kept it entirely on a fresh water lake that my neighborhood has a boat ramp on, and I've mainly only done hull cleaning to get lake scum off before putting the boat away.

Yesterday, I took my boat out on the lake. It has had an issue with one cylinder not running properly at low off-idle RPMs (between 1500 and 3200). I idled to a location with some vegetation and shut the engine off. After I paddled out of the weeds, I tilted the motor out of the water and removed the weeds from the prop, then trimmed it for running. I mentione this because it might be important for the next events.

I started it the engine, idled away from the shoreline, and brought the boat upon plane. The engine stuttered intermittently a few times during this process like it missed spark, so I thought maybe the plugs were fouled or there was some other small issue that an "Italian tune-up" would fix, and I went to WOT. The engine proceeded to max RPM (5700) and the boat ran at the maximum speed this engine will push the boat at (32mph on my depth finder, 30mph on GPS). I proceeded to the opposite end of the 7 mile long lake at WOT and dropped back down to idle when I reached my destination. I allowed the engine to idle for the next 15 minutes or so, intermittently placing it in gear and then back in neutral to push the boat past weeds.

When my activities in that area of the lake were complete, I idled back out of the cove I was in, and advanced the throttle to bring it up to 3200RPM. It ran briefly at that speed and then the engine stopped suddenly. I raised the propeller out of the water to check for debris and found none, lowered the motor back into the water, and attempted to start it.

After several tries, re-priming several times, I was able to start it again, but it would only run at fast idle in neutral. When I pulled the lever to low-idle neutral, it died. I could re-start it again and get it running in fast idle, but when I tried to quickly shift it into gear and keep it at a faster engine speed, it died again.

A good samaritan on the lake towed me back to my point of origin.

At home, I removed the cover and lower shrouds, checked the compression (90psi on both cylinders), checked the spark plugs (slightly wet, but not carbon-fouled), and proceeded to remove, disassemble, and clean the carburetors. I found the carbs clean, but noted that the vacuum line to the bottom carb had broken. I reassembled everything and remounted the carburetors, then primed the fuel bulb and noticed gasoline running out of the mouths of both carbs. So, I took them back off again, replaced the needle and seat and float on both carbs, and reassembled. After reassembly, the carburetors didn't leak fuel when I primed, so I reassembled everything and put the boat back on the water.

It ran well at idle, ran better than before at off-idle, but not perfectly smooth (as if one cylinder was weak, but not dead), and I was able to bring it up to top speed on a quick upwind and back jaunt from my boat ramp. After I was lined up with my trailer and would coast back to my trailer. It was good that I did.

To test whether the engine would restart, I stopped the engine, then restarted it, and the previous issue resumed, and I needed to manually crank the boat up the trailer because the engine wouldn't run in gear.

The boat is back in my driveway now and I'm going to:
1. Check to make sure the carbs aren't overflowing again.
2. Replace the inline fuel filter on the side of the engine.
3. Take a look at electricals, specifically the ignition module, connections, and the coil.

If the carbs are overflowing again, I'll make a trip to West Marine for some new needle and seats, and new floats. The ones I used may have been used before by the previous owner, and might have performed well on the bench but then soaked up gasoline and allowed overflow to occur.

The inline fuel filter has never been replaced, and when I drained the carbs and then squeezed the bulb to refill them, it sounded like there might be a minor fuel blockage.

The coil has never been replaced, and the symptoms could be due to a failing coil, ignition module, or weak connections.

DW

 

[boobie]

Check your spark when the mtr acts up. It should jump a 3/8" open air gap.

 

[webbd]

Thanks,

I need to find my spark gap tester. I think it was in a location that I coudn't get to until today. Or maybe I can try holding it with some well-insulated pliers. I just don't really enjoy the invigorating feeling when a spark jumps through my body. I think I'm getting too old for that.

I received and installed a new coil yesterday afternoon (Sierra P/N 18-5170, replacement for OMC P/N 0583740).

I also went to West Marine for a new fuel filter (Sierra p/n 18-7830). Plus, I bought 2 new carb kits (Sierra p/n 18-7222).

The new carb kits were because after rebuilding the carbs, I still saw leakage from both carbs after pumping them up. I may want to disassemble the lower carb one more time and adjust the float downwards just a bit the next time I have it off, but for now, the tiny little weep from the emulsion tube into the venturii chamber is slow enough that it doesn't worry me much, even for idle (1 drop every 5 seconds or so, not a drop every second).

I haven't tested yet due to weather and will need to pull my boat into the garage this evening because it's going to rain again. Hopefully I'll be able to test soon.

In addition to all of that, while running the engine yesterday in a tub of water for back-pressure, I found some smoke coming out from under the engine. This spot is in-between two ribs that reach forward on either side of the engine base, so I can't inspect to see where the leak originates. I'm ordering Sierra 18-0128 to replace it.

 

[boobie]

What did you find out with the spark test ???

 

[webbd]

I was able to test it out this morning before the rain arrives from TD-19.

Verdict: Bad 22 year-old coil.

I didn't search for my spark tester. Instead, I just tested it.

On the driveway, the engine started quickly and ran stronger than before. I considered whether I should turn the idle down, but with no backpressure, I decided to wait until it was on the water.

The wind is out of the southeast, and my boat ramp is on the west side of the lake, so I was be able to drift back to the ramp if necessary as long as I limited to upwind/downwind tests while keeping the boat ramp downwind.

On the water, the engine idled in gear without stalling. That's something I've worked to get it to do since I bought the boat 9 years ago. At low RPMs in gear, it still hinted at a misfire, but less than before. I think that further float adjustment on the lower carb and possibly some other low-speed adjustments on one of the carburetors might address ths issue.

For the first time since I've owned the boat, I needed to throttle back. It reached 33mph at full throttle and exceeded the manufacturer's redline by 250RPM, maxing at 6K RPM. Throttling back to keep it in-line seemed to be a good choice.

To be safe (due to the wind and also due to the failure last weekend), I stayed on the south end of the lake, but was able to test it out thoroughly.

I still need to lift off the powerhead and replace the base gasket, but I'm pretty happy about how it's running now.

- DW

 

[iggyw1]

Might want to go with a different prop to get those RPM's down a little at WOT, and still get top end speed without cutting back on that throttle.

 

[webbd]

Agree. I might take the prop in to get pitch changed,

 

[iggyw1]

Agree. I might take the prop in to get pitch changed,

Just remember, changing the pitch may effect you getting up on plane as quick, but you won't be going over your "red line" on RPM's, so you just might want to consider picking up a good used prop with a higher pitch and keep the one you have as a spare if you need to get up on plane quick for water sports other than just fishing. (such as skiing).

 

[ct1762@gmail.com]

those motors are fine running 6k with a light load. did you test the coils for resistance? that leaking at the emulsion tube is common but nothing to worry about. you can patch it if you want. but the real reason for my comment was in your posts, ie. running kinda crappy then not restarting... sounds like water in the fuel to me! i'd take a look at that gas, pour some in a clear jar and check if it's cloudy.
also, 90psi, even though your tester could be reading low and they are nice and even, does sound low for that motor. i have one in the shop... a 1991 40hp that reads 123 and 135psi. just a thought... could be the skirts are getting tired.

 

[webbd]

@iggyw1: Thinking about it some more, I used to have another prop with a taller pitch and this one was my spare that I bought for when I wanted to pull a tube, but the other prop's hub was damaged and can't be re-hubbed any longer. I probably need to get another taller-geared prop again.

@ct1762: I haven't tested resistance on the old coil unit. I need to look up the correct resistance and testing procedure. If it's a heat-soak failure, is there a possibility that resistance increases or reduces only when it's hot? This is a moot question because I already installed the new 2-coil assembly, but has anyone installed 2 single coils instead of the double unit on one of the 737cc 2-cylinder powerheads? It doesn't look like this is a lost-spark application where both plugs fire simultaneously.

 

[webbd]

Update:

I finally took some time to tune the carburetors again while on the water after all the other work I did on it.

This engine has always had issues with one cylinder dropping out at lower RPMs, and it's bugged me for all the years I've had it. Once over 3200RPM, no issues. Below that, it would run smoothly for maybe 10 seconds or so and then start running on only one cylinder.

Issues addressed over the years:
1. That stupid timing advance roller. I replaced it a couple of years ago. Looks like I need to plan on replacing it again soon, but it's still usable for now. The cam slot is really tight on the roller when timed according to specs.
2. Carburetors rebuilt and floats set where it doesn't puke fuel every time I squeeze the primer bulb.
3. New coils - the reason for this original post.
4. New ignition module years ago before I bought the boat from a friend.

Now after the new coils, and carb rebuild/float adjustment it ran better than it had since I purchased it, but still dropped out one cylinder at lower RPMs, it just waited maybe 30 seconds instead of 10. Progress made, but not good enough.

On the water,
- I put on my wrist lanyard first. I was the only one on the boat and wanted the engine to die if I managed to fall overboard into alligator-infested waters.
- I rotated the wheel all the way to the right so the adjustment screws on the carburetors would be easy to access. I had already removed the engine cover (it's loud at full throttle without a cover).
- I started the engine and put it into gear at idle. Starting with the top carb, I turned the low-speed mixture screw 1/4 turn at a time, first inwards until it stumbled, then outwards until I had a good feel for midpoint. Rinse and repeat with the lower carb.
- I raised the RPMs to 1700, then did the same.
- Raised the RPMs to 2200 and repeated.
- Raised to 2800 and repeated again.

When I was done, the engine ran without misfiring throughout its rev range, although I did note the occasionial moment when it would misfire 3 or 4 times and then resume running normally.

After a bit of further testing all rev-ranges to my satisfaction, I returned to the boat ramp, where I promptly ran out of gas while loading it onto the trailer. What luck!

- DW