'86 40hp, one cylinder doing all the work?

[Noltz]

Full story; I went out with 4 people in our 15' MFG 'glass boat. Engine was behaving just fine. It's de-VRO'd, running 40:1 premix. We trolled out of the harbor and slowly moved away from the small sailing craft nearby. A brief full-throttle push to see how long it takes to get up on plane with a 'full load', responds nicely and got up on plane for ~30 seconds. Throttle down and turn around, cruising along at about 2/3 throttle for about 10 minutes taking in the sights. We're plowing but high in the water, engine sounds happy. 2 miles out from dock I push the throttle open again and I feel the engine bogging. I pull back and the RPM starts to drop. Boat lowers in the water. Fearing a stall I open it back up again and the engine is maintaining RPM but struggling. Probably 5mph, WOT. Took a good 20 minutes to get back to dock. Once there I throttled back to idle it actually maintained idle but it was clearly operating on one lung.

The carbs were clearly leaking around the bowl gaskets and poured fuel when I tilted the motor up to launch/recover. I figured some varnish had come loose and plugged something in one carb. Carbs were removed and sat in cleaner for 3 days. Rebuild kits installed (no floats were included but buddy said they were perfect). Floats were set equally at 3/4". Fire it back up on muffs and it sounds like it's running ok, but there's occasional miss fires. Responds to throttle snap nicely, but definitely cutting out at idle. Here's the fun part; Pull top plug wire, engine nearly stalls. Bottom plug, barely any difference. 150psi compression top, 135psi bottom. Bottom plug is wet with gas, top is dry, both electrodes are cold to the touch. 115? @ upper plug, 100? at lower plug. Found 243 ohms secondary resistance on both coils. Swapping plugs and/or wires did nothing, top cylinder still doing all the work. Noticed fuel spitting from carbs at idle with the silencer off. Engine seems smoother at idle when I apply a little pressure to the fuel bulb. Also noticed very little water from the telltale.

Here's a 2:30 video of it running. Any opinions on this? I don't want to get out on the water again and have it fail on me again.



Edit; at 1:50 the RPM comes up. Buddy had lifted the high-idle arm a bit, then lowered it. It was not a flare-up.

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

When did you last do the impeller?
Are you sure bottom plug isnt wet with water?

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

Check with your palms that both of those carbs are pulling the same vacuum

 

[Noltz]

Re: '86 40hp, one cylinder doing all the work?

I do not know when the last time the impeller was done. It's on the to-do list. It doesn't seem to be overheating using the temp gun. Highest I could find after idling for 10 minutes was 130?. The plug smelled of fuel, not water, but I didn't try using a flame to dry it. Blew it dry and swapped plugs around. No change.

I'll check that, thanks. What can I do if the bottom is not? I don't see any method to sync them. When I had my last bike it was a '02 Suzuki SV V-twin. You could adjust the throttle linkage so both carbs were pulling the same.

Ninja Edit; We also went and got fresh fuel and mixed it 50:1. No change.

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

Have you checked your bottom plug is sparking?
Also check your butterfly linkages havent come loose

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

Your link and synch looks all ok from what i can see.
These i think have one poppet valve independent of the thermostat so you may get enough water pressure at idle but when you increase the rpm there may not be enough to open the poppet- which will cause overheating.

Did your overheat alarm go off?
Have you tested it by grounding it to the block?
Ive seen these run on the wrong impeller so no water flowed through. Gasket normally goes but the rest of it stands upp fine

 

[Noltz]

Re: '86 40hp, one cylinder doing all the work?

The alarm is long dead, unsure why (the piezo is melted in the controller). Come to think of it ill wire an external buzzer for it... But that's another issue. Goin along the overheat line of thought, would it be the head that warps? You think thats whats wetting out my plug? I have pretty decent compression and it didn't change when I put oil down the cylinders. I can get a leak down tester from work. Can I put a two stroke to TDC and check it the same way I can a car engine?

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

You need to check your bottom spark is sparking too.
Yes you can do a leakdown on an outboard.
Yes the heads do warp if they have overheated, you do need to do the impeller so you have a good waterflow and you then know when to schedule in its next change.
When you have the LU off put a hose onto the water intake pipe and see if you can get water coming out the peehole. You need to find out why thats not squirting water.
The heads can be sanded down on glass and sandpaper to get straight again so no issues there unless its really out of whack. You can try retorquing too.
Yes you can do a leakdown test, im not sure if that is whats causing it, but if you find you are getting spark there and the plugs are wet id say its getting likely

 

[Noltz]

Re: '86 40hp, one cylinder doing all the work?

Both plugs are sparking. We removed both, grounded them and cranked it to check. I did swap the plugs and wires (separately) to see if anything changed. No matter what combination of parts it was always the top cylinder that did all the work. My technician buddy is swapping the carbs top and bottom to see if it's a carb issue. It's really just odd how it'll miss once or twice, and how they're both so cold. Am I correct that these are fixed jets and there's no adjusting mixtures? It was a VRO motor.

If buddy hasn't found anything I'll go ahead and order a new impeller. It's only got maybe 25 hours on it but it's years old. I was hoping to get one more season out of it. I went down to the launch today and listened to a few other Johnsons (including one very similar to this one) and it had the same random miss, but he seemed to be experiencing the same off-idle issue I used to have before the carbs got cleaned. Poor guy restarted 6 times before he could get under way.

Quick edit; I noticed on another thread (http://forums.iboats.com/johnson-ev...hp-johnson-misting-fuel-out-front-620851.html) the OP describes the same situation I have with both my carbs, that they're misting fuel out the front (at least at idle). But my engine is responsive (at least with no load on it). Don't worry about it?

Thanks for your input on this. I truly appreciate it. Next step is to find an old seadoo and cut the bottom out of my boat

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

Yep, i know slightly what that guys thinking, i park up at the ramp some lunch breaks to see such things happen. The boater who starts his boat for the first time of the season after putting it in the sea is always good to watch down there, especially when he rushes his car to be first down the ramp.

Your engines impeller may not have many hours on it but the impeller will of set through sitting around, it loses its ability to flex which is how it works to pump water. Its good to run the motor a little and often to minimise that happening, so your impeller will need changing.

Have you tried putting your hand over the bottom carb to check it has vacuum?
Interesting to hear if changing carb makes a difference.
Wet plug yet having spark indicates too much fuel or water.
I wouldnt cut the bottom out yet, make sure insurance is up to date too!

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

The last one of these i worked on had a butterfly choke.


yours has the newer solenoid primer.
Does the primer have lines going to just one carb or both?

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

And yes, those idle jets a fixed orifices

 

[Noltz]

Re: '86 40hp, one cylinder doing all the work?

Yep, I've read about and watched a few videos on the impellers and how it's important they flex to seal to the housings. Age will hinder flexibility, which means it's time for a new one. Primer line actually injects directly into a port in the crankcase if I recall correctly. Last year I had big time carb issues but I needed to take it out once to make sure the boat was worth saving. I removed and cleaned the carbs, no new parts, and it ran fine until I put it in the water. I had to tap the primer to keep it running. We were out for 15 minutes just tapping away. I tried tapping it again when this all happened, no effect this time. It's got 150/130 compression but I did not specifically check vacuum at each carb. Nick (technician & friend) closed up his garage for the long weekend here, so there'll be no progress for a few days. I'll post up again when I have more info.

Really sounds like I should slip an impeller in there at any rate. If it needs head work because of a blown impeller, it'll just happen again without fixing the cause.

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

One other thing to check when the garage is open again is that the primer solenoid hasnt got stuck open and is pulsing continuously into that lower crank port and flooding it.
Just pull the line when its running to make sure its shut off

 

[Noltz]

Re: '86 40hp, one cylinder doing all the work?

Digging this up for conclusion. Didn't get this sorted until about a month ago. I had a local marine tech replace the waterpump & go over the carb rebuild. Tech said the carb rebuild was excellent and perfectly in sync, and the waterpump was "quite hard". It now spits water like crazy, and runs like a champ. I only got 2 good days out of it, and the second one cost me the prop... or at least a good bite out of it. Alwell, they never said boating was cheap. There's always next year.

Thanks to all that helped.

 

[Bosunsmate]

Re: '86 40hp, one cylinder doing all the work?

check you dont leak gear oil out from the prop incident.
cheers