Johnson 15 HP (1988) dies when coming down off of high speed.

[The Famous Grouse]

I have a 1988 Johnson 15 HP. It has factory e-start in case that matters. Bought as a seriously neglected motor that hadn't been run in years. To get the motor running, I took the carb off and disassembled to clean using carb cleaner and compressed air. But I did not remove the "plugs" to clean under then as I did not have a new carb kit with replacement plugs. Bottom line is that I undestand that I did not completely clean the carb and there is potential here for issues.

After cleaning and returning the needle to the standard setting, I got the motor to run, throttle up, and idle, so at this point I was thinking I may have her up and running.

Now the last problem. Had it out on a boat for a test run yesterday. It started fine, idles fine, and runs at low speed all the way through WOT fine, including no bogging or stalling on a fairly sudden throttle up.

Now the problem. When running at higher speeds, I'd say greater than half throttle (15-20 MPH with a 14 foot Jonboat) for anywhere from 30 seconds to 2 minutes, and then throttling back to a lower speed (but not dumping it all the way to idle suddenly. Just doing as you would normally do to bring a boat off of plane when approaching a landing for example), the engine suddenly stalls and dies somewhere below half throttle.

Restarting is then very difficult. The engine acts as if it was flooded, but I'm not absolutely sure if it is flooding out, or dying of fuel starvation and then flooding after repeated cranking trying to restart.

Letting the engine sit for a minute or two will usually produce a restart, but choking and some extended cranking is required. When it restarts, I have to run it at highest neutral speed for a minute or so, or the engine will die if I try to throttle back to shifting RPM too quickly.

But once I can slow the engine down to get it in gear, it then runs fine again. Until I try to come down off of a throttle >about half, then the issue repeats.

Any ideas what could be causing this? What should I try? Suggestions and advice please.

Many thanks.

Grouse

 

[Rick.]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

did you do a link and sync with the carb. after you re-installed it? Have you checked your compression? Best of luck. Rick.

 

[Tim Frank]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

Bottom line is that I undestand that I did not completely clean the carb and there is potential here for issues........

Any ideas what could be causing this? What should I try? Suggestions and advice please.

Many thanks.

Grouse

Completely clean the carb

 

[The Famous Grouse]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

Thanks for the replies so far, both confirmed what I was thinking as leading suspects.

To Rick, no I didn't do a link and sync, but I thought this might be a possible cause. Good to validate that could produce this issue.

To Tim, I understand that a clogged carb could still be the issue. My dilemma was that if I take the carb off, I feel like I might as well install a full carb kit rather than messing around with cleaning and reinstalling.

Here's what I'm thinking as far as order of operations:

1. Link/sync proceedure. Then if that doesnt' fix it...

2. Remove carb, clean, install full carb kit.

What do folks think of that?

Grouse

 

[Rick.]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

That is as good as your scotch. LOL. One of my favorites. Rick.

 

[The Famous Grouse]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

That is as good as your scotch. LOL. One of my favorites. Rick.

Scotch??? I object to the consumption of liquor in all its forms, making exception only for beer, wine, and occasionally spirits. But only for medicinal purposes, obviously.

Grouse

 

[Tim Frank]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

The fact that you described the motor as "severely neglected" suggests that a deep clean is needed.

 

[the machinist]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

When you power down, you might have the fuel primer bulb in hand, as soon as it starts to sputter, pump the bulb. If it picks up & does not die, that would pretty well suggest it may be starving for fuel somewhere in the system.

Those plastic topped carbs are pretty simple & easy to work on, so you may even get by without a kit. They however need to be CLEAN.

 

[The Famous Grouse]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

I'll give the fuel bulb test a try when I do the link/sync and see if that produces anything.

The one thing I'm on the fence about is this: Given a carb kit is $25, is there any point whatsoever in tearing down the carb just to clean it? The risk I'm seeing is do all that teardown and cleaning, then put it all back together, then test, and then risk repeating the whole process if the cleaning alone doesn't fix the issue...

If time = money, what would you guys do?

Grouse

 

[Rick.]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

If time is a concern and you plan on using the motor as your main engine I would put a kit in it. I hate breaking down in the summer when I'm supposed to be fishing. Having said that, I think carb. kits are probably replaced way more often than necessary. Rick.

 

[Tim Frank]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

If time is a concern and you plan on using the motor as your main engine I would put a kit in it. I hate breaking down in the summer when I'm supposed to be fishing. Having said that, I think carb. kits are probably replaced way more often than necessary. Rick.

But he did say "severely neglected"....

 

[Rick.]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

That's true and why I would just do it. "Severely neglected" IMO might mean he never waxed it. LOL. I am a bit anal. I picked up a 3 HP this winter and I changed everything cause I want to use it for my kicker this year. Last thing I did, was wax it. Rick.

 

[Tim Frank]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

That's true and why I would just do it. "Severely neglected" IMO might mean he never waxed it. LOL. I am a bit anal. I picked up a 3 HP this winter and I changed everything cause I want to use it for my kicker this year. Last thing I did, was wax it. Rick.

Was that just to make it look great....or to cut drag through the water?
Enquiring minds....etc.

 

[The Famous Grouse]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

But he did say "severely neglected"....

To put more details around that, the engine had been left sitting out on the back of a boat in a non-running condition after it failed to start one time. The previous owner used it "a couple of times a year". He did get it running he claimed, but then it wouldn't idle down and was hard to start, so he started "working on the carb" Whatever that means.

He then let it sit in his back yard for 3-4 years without doing anything to it. Then there were some thefts in the hood, so he figured it was sell it or get it stolen, so he put it up for sale in October and since it was non-running, it sat on Craigslist forever. I finally scooped it up for $200.

The cowling had a hole busted in the top about the size of a quarter, so water had been running through the cowling and into the engine compartment. Then, at some point, someone had "fixed" the hole by smearing about an inch of bathroom caulk on the top of the cowling. It looked like a 15 HP johnson with a layer of vanilla frosting on top. Nice.

The bottom line is that it hasn not run in at least 4-5 years and probably the carb was gummed up from lack of use. He was also, most likely, running old, foul, stale gas through it.

But the compression checked out, AND it was a rare short shaft e-start model, so I figured I'd gamble. I repaired the cowling and did a factor-color match paint job on it so it looks very good. I also fixed the electric start, so that makes it very desireable as there are very few short shaft 15 e-start models out there.

The carb situation is the last hurdle.

Many thanks for all the suggestions.

Grouse

 

[FishingRat]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

TTT!

Did this issue ever get figured out? Having a similar problem, where starts right up, idles fine, can run at different speeds, then when I come down after full throttle the motor dies then I can't start again. After I let it sit for a while, it will start back up, but then I immediately have to full throttle to keep it running. Then it kind of sputters and bumps as if it's missing, and sometimes will work through it to run well at full throttle, only to stall when I come down again; or it will die after it starts, then I can't get it started again.

Will try bulb test. I probably have to clean and rebuild kit the carb, as last owner ran it, but let gas sit for about a year.

So, famous grouse (probably my second favorite scotch) did you ever solve your problem?

Thanks,
Mark

 

[racerone]

Re: Johnson 15 HP (1988) dies when coming down off of high speed.

Do a compression test first.---Post results then go from there.