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2015 Merc will not throttle up without choke...


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Starts fine. Idles fine w/o choke.  Beyond idle bogs down and cuts out as if starved of fuel.  So...will check the hoses/connections for air incursion, but guessing its carb jet foaling.   Doing the Sea Foam et al dance will probably not solve the problem and will just replace the carb.  Rebuilding a carb is a PIA that is fraught with issues.  Life is too short.  

Anything I am missing?

Thanks in advance.

 

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Take the bowl off the carb. Remove float and needle valve. Clean any goo.  Blow carb cleaner up thru the valve seat. Put it back together. Almost always works. Any accomplished yachtie or fisherperson has done this miles from land. 

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You can pull the carb with the tool kit that came with the engine, only took me three years to figure out....you stack the box wrench things and can get back to the hard to get bolts. As above usually a tiny bit of goo or water in the bowl plugging the jets, just blow out put back together and off you go.

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Clogged main jet. You might be able to blow it out or may have to unscrew and clean with fine wire. Easy. No, you do not just replace the carb. You also do not need to rebuild the carb (not old), only clean the jet.

Then consider why this happened.

  • Is there a fuel filter (some do not)? If not , add a mower filter in-line.
  • Use an additive (Seafoam, Stabil 360, Biobor EB) all the time. Prevents aluminum corrosion in the bowl, which is probably the problem.
  • Keep the tank vent closed unless actually running. It does not take much humidity or rain splash to add enough water to increase corrosion (does not have to be enough to separate).
  • Try to run the motor every few months. Try hard.

 

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Unleaded gas will produce a deposit on the bore wall of the main jet, reducing its size and leaning out the mixture progressively, requiring more and more choke to keep the motor running. Get a new jet or the proper size drill bit to ream it out (by hand).

Second the motion to keep the vent closed.  A partial tank of gas will "thermo-pump" - at night, the fuel will contract, sucking the local ambient (moist) air in; the alcohol in the unleaded will absorb the moisture; the next day, the gas will expand, venting the now dry air, ready to repeat indefinitely. I have drained a 1 quart tank and found it to contain about 1/3 water !

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  • 2 weeks later...

Even with cheap carbs available, I would suggest you fix the current one. You won't always have access to eBay or Amazon and knowing how to clean out your carb is a very handy skill and easy to acquire. 

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Thanks all. 

Yard re-built carb before I could check the fuel hose.   No joy.  So checking the fuel hose is next.   Engine was "winterized" a few years back and is probably a mess from sitting with e-gas all that time (I am assuming they did not drain the float bowl etc)  When I have rebuilt carbs in past I too had no joy.  New carb?  Joy.  I guess I (and the yard) suck at rebuilding carbs.   

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1 hour ago, sail69 said:

  Engine was "winterized" a few years back and is probably a mess from sitting with e-gas all that time (I am assuming they did not drain the float bowl etc) 

???

You should never store an engine with gas in the system.

Start it, shut off the fuel line, rev the engine until it runs out and stops then drain the tank.

Using some RPM helps to better clear out the system - it can die when the fuel gets a bit intermittent if run at idle.

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On 9/18/2021 at 6:44 AM, 69sail said:

Yup.  SOP here.  I use e-gas and drain the carb every winter.   However, I did not winterize this engine.  The yard did.  No my yard, so who knows what they did or did not do.  Given symptoms, my guess is they did not do.

I think your Merc is a lot like my 2007 Tohatsu (who used to make the small Merc outboards. Maybe they still do). I like my 6 hp Tohatsu and it is reliable, except on the first day of the season. I run my carb dry, avoid ethanol fuel, and store my OB over-winter in a dry place. I have a fuel filter. I also pray to the deity of small outboard engines and speak no ill about the old testament according to Seagull. And it does not seem to matter. Perhaps 15 percent of the time the carb will only idle, or (the worst) will rev in N but will sputter under load on the first day of the season. I have become proficient at pulling the carb, field stripping it, and blowing the orfices w/ compressed air. The orfices are small and easily clogged by the tiniest hint of grit. 

All of this is to say that your yard may have drained the fuel bowl and/or run the carb dry, as they should. But that does not ensure a happy carb in the spring time. There are one or two threads of recent vintage here on Tohatsu's. They are worth reading, as along with good advice there is a long list of rituals and conjecture about what causes carburetoris noworkus. 

Snubs

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