Outboard won't Idle

[Wolverine]

I have a 1985 Nissan 5hp 2 cycle 25" shaft outboard with an external tank. It came with the 1985 Compac 19/II when I bought it in 2010, but having a new 2010 Tohatsu 4hp 20" shaft outboard, I never used it. In 2018 I had a new carburetor, impeller, and spark plug installed in both. I continued to use the Tohatsu until last year when it refused to start. So, I placed the Tohatsu in storage and put the Nissan on the Compac, filled the tank with ethanol free gasoline and the proper amount of stabil, and she ran flawless through her last sail in December. Before placing the outboard in the garage I ran it until the fuel in the carb ran out. This spring I placed it on the Compac and although it always starts, it won't idle. This makes it difficult when coming into dock and not good when shifting into gear. It will only continue to run with the accelerator at least 1/2 open. This afternoon I removed the Nissan from the boat and placed it in a barrel filled with water. I started it and sprayed inside the carb with Lucas Oil Deep Clean GDI. Tomorrow I will replace the gas with new and add Seafoam.
The gas in the tank is left over from last season.
I am not a mechanic, nor try to be. Can anyone tell me what is wrong?
Please respond as if you're writing an "Outboards for Dummies" book.

You cannot view this attachment.

[Charles Brennan]

Wolverine, It's not really "Outboards For Dummies"    so much as it is "Carburetors For Dummies" that should be concerning you.
Unfortunately, this is not something that can be dumbed down that far; so let's start with some (boring!) background data, and go on from there.

Internal Combustion Engines (ICE) rely on what is called a "stoichiometric ratio", a precise ratio of reactants required for complete (or at least, reasonably efficient) combustion.  The ICE stoichiometric ratio is 14.7:1, which is to say there are 14.7 pieces of air, for every piece of gasoline.

How do they achieve that ratio in a carburetor?
They suck up fuel into a narrow tube called an emulsifier tube to disperse the fuel into the tiny pieces of fuel that achieve that 14.7:1 stoichiometric ratio.
If you've ever squeezed a spray bottle, you've witnessed liquid emulsification. 
Women have been doing it for centuries:
You cannot view this attachment.

Engineers do all their calculations and wizardry and figure out how big around and how long to make that little emulsifier tube to achieve their magic stoichiometric ratio and make the engine run.
When that carb left the factory, EVERYTHING was the perfect, diameter, length, pressure, and whatnot inside that tube to achieve this, and your motor ran GREAT!!   

Here comes the problem:
VOC's (Volatile Organic Compounds) like, ya know, gasoline, tend to leave behind deposits when they evaporate.  The usual term for these deposits is varnish, because it resembles a brown, sticky substance similar to varnish.
This happens every time there is fuel left in a carb to evaporate and leave a little residue (varnish).
And the next time.
And the time after that.
Once enough varnish builds up on the emulsifier tube, SURPRISE!!  There is no longer the ability to achieve the ideal stoichiometric ratio inside that carb. The walls of the tube have become thinner, because of the build-up of varnish on the walls of the tube. Since you can no longer mix enough fuel with the available air, particularly at lower RPMs, the engine won't idle.

This problem is even worse in 4-stroke engines, since they don't have to emulsify fuel that also has large amounts of oil mixed in.  This allows the Engineers to use even tinier emulsifier tubes which: (You guessed it) Clog up even FASTER than 2-stroke emulsifier tubes. 

A lot of times, if you can adjust your carb's choke plate, you can manually restore that stoichiometric ratio and get the engine to run like the Engineers envisioned.
The proper solution, of course, is to take apart the carb, apply solvent inside that emulsifier tube, until it is squeaky clean and maintaining the air/fuel stoichiometric ratio necessary, for proper engine operation.

I used to resign myself to re-building carbs every other year, or so.
Eventually, I came up with the idea of:
Hey! Let's see if we can keep those tubes from having gas evaporate inside them, when I'm not using the engine! 

Solution 1:
The accepted method is to unscrew the carb bowl and allow the gasoline to drain.
Nothing in the carb, then nothing can evaporate inside those pesky tubes.
That does, in fact, work, but then we run into Brennan's Technical Aphorism:
"The Solution To Any Technical Problem, Creates A Brand New Technical Problem"   
Namely, trashing the carb bowl gasket and the carb bowl bolt's gasket and maybe the bolt threads, as well.

Solution 2:
Run the gas out.
After arriving at the dock, or when test-firing the motor, do not kill the ignition, disconnect the fuel supply and allow the engine to run out of fuel.
No more gas in the carb!! 
Well, not quite.   
As the fuel runs out, that pesky stoichiometric ratio gets out of whack again and the engine runs "lean" (not enough fuel for the fuel to air ratio) and stalls.
With a little bit of fuel still in the carb.  To be sure, there is not enough to gunk up the tube like if the carb bowl was full, so all this really does is to buy you some more trips, before the emulsifier tube DOES clog up again.

Solution 3:
Same as solution 2, with one wrinkle:
Use the choke.
Choking off some air as the engine starves for fuel and runs lean, restores that (in chorus, now) stoichiometric ratio, until it become completely starved of fuel and then stalls.
Suspenders and Belt addendum:
Put the choke on full and restart the engine a few times, until it will no longer start up.

Solution 4:
Hedge your bets.
Start with Solution 3 and then I also use a product called Sea Foam, that purports to be a top engine overhaul/cleaner and directly goes after deposits such as, uhhh, I dunno, VARNISH!! 
You cannot view this attachment.
I add it to every tank of fuel that goes to any of my gasoline powered tools or engines.
I have not had to re-build a carb, for many years and my engine starts much more quickly and idles (nearly) as low as I choose. 
For full disclosure, I spent the time at the dock, adjusting the low speed idle on my 1995 15 hp 2-stroke Johnson outboard, until I could put it in forward gear (tied up at the dock) and idle at 500 RPM.  You have to use the kill switch if you want to turn off the motor, although I prefer to disconnect my fuel hose and tap-dance on the choke knob, until I'm reasonably certain there is little to no fuel in the carb.  I re-built this carb just this past winter, and when I got it apart, I discovered it was clean as a whistle and there was another part (cam follower) that was mimicking the carb symptoms.
The time before that was in 2004.
Color me a Big Believer in Sea Foam.

Mickey Mouse Solution 5:
When you've gotten lax about getting fuel out of the carb and alluva sudden-like, your motor won't idle any more, what I do, is to put a little more Sea Foam in the tank than usual and then run the motor at the highest RPMs I can manage (short of red-line RPMs!)    and periodically (every 10 - 20 minutes or so) run it back down to close to idle and listen.  If it starts to malfunction, I immediately rev it back up again and after a few minutes, test it at idle RPMs again.  The stuff will really clean out an emulsifier tube, so that a carb re-build is un-necessary. 

Hope this helps,
Charles Brennan

[Riley Smith]

I agree, less than a carb clean, that would be my tactic. I ALWAYS run the motor when I go out because our little motors get kicked around and not used a lot. The BEST thing for an outboard is to RUN it. Not for two minutes, either, but enough to warm totally up. The Honda will not crank on the first pull but it cranks. And runs. I'm keeping my fingers crossed.

[Wolverine]

This morning I refueled with ethanol free and put twice the recommended amount of Seafoam in the tank. Ran the Nissan for about 5 minutes constantly throttling up and down. Then I reduced throttle and let her run while I went to the garage to get the Tohatsu. When I returned she had stopped. Still won't idle. I found my notes from last spring on the Tohatsu. I had emptied the internal tank and poured straight Seafoam into it. Pulled the cord 10 times and left it on the stand. I'm going to play with that for a bit before calling around to see if I can get either fixed before my trip on the 17th.

[Wolverine]

The Tohatsu didn't show any signs of life. Checked for a spark, yes. Check it was getting fuel??? Took off the fuel line from the tank and the carb. No sign of fuel in the lines and the filter was dry. Blew the entire fuel system out piece by piece with high pressure air into a rag. Orange, white and brown gunk. Reconnected the fuel line to the internal tank and carb and it fired up on the first pull. Let it idle for ten minutes then clamped it on the back of the Compac. I'm glad that worked out. My next two options were to see if a shop could fix one of them by the 16th, or have the Provision Company in town order me an expensive new propane outboard.   

[pgandw]

Instead of spending money on "an expensive new propane outboard", add less than a boat buck and get an electric outboard.  Your shoulders and ears will give you thanks for your remaining time on Earth.  I chose the Epropulsion Spirit 1.0 as the cheapest electric outboard suitable for a 19ft Mariner.  It will certainly power your Compac 19 just as adequately.

I motor more than I used to because it's so easy and comfortable.  Range on the Mariner is an honest 12+nm at 400 watts which gives 4kts for 3 hours (tested against my GPS).

Fred W
Stuart (ODay) Mariner 19 #4133  Sweet P
Yeopim Creek, Albemarle Sound, NC

[Wolverine]

I did think about it, how is it in our waters with all these canals and narrow rivers on the ICW? I want to be able to go out for a week or two and not worry I can't gunkhole too much.