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baytech05

Outboard Problems, any ideas?

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Morning Guys and Gals,

 

I spent the past two days fishing or trying to fish Oswego with outboard issues. I have a 40 horse mercury outboard (11 years old) with a portable six gallon fuel tank. Here is what's going on, the engine starts fine but will stall at idle in  both neutral and in gear. It will start back up fine, then run for a little and eventually stall. This will continue for at least a half hour to an hour until the engine warms up and then it will run fine at idle trolling for the rest of the day. Now the second part of the problem, I will run it full throttle on the way in for maybe 2-3 minutes until it starts to gradually loose power (while still at full throttle). Once that starts to happen I let off the throttle, back to idle and repeat the process. 

Here is what I have done so far. replaced eternal gas tank and fuel lines leading to engine (thinking I had some air leaking in), and replaced the fuel pump.

 

Any thoughts, ideas, suggestions?

 

Thanks,

Baytech

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#1 If possible run the engine in the dark checking for sparks [ my lesson the "hard way was a loose bolt holding the power pack and the GROUND ; sparking was clearly seen in the dark ] easy fix to tighten bolt . I cleaned up ALL electrical contacts then put on " dielectric grease " [no further problems ]also ran a separate ground a lesson I learned from having a Chev. Vette !]

#2 Does the engine have a thermostat and does it work.

#3 Carbs or FI. carbs may have to be rebuilt.

#4 check or replace spark plugs.

#5 Check compression as a last resort ; if so use a gauge that screws into the block not one with a hose [ will give a low reading ]

Let us know if you get a fix !

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Mea copa on the fuel filter but lesson #1 I was told by a fisherman I started with 30 years ago was to always FILTER your gas before putting in the boat's tank ( amazing the amount of debris in that funnel screen ).

Started to use a new filter from Hopkins Mfg. Corp. " Removes Water, Dirt and Debris from Fuel " Made in U.S.A. Anyone have an opinion ?

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The filter was in good shape, checked it when the fuel pump was replaced. 

I will check the ground issues, replace the spark plugs, and will purchase the carb kits to rebuild. It will take awhile to get everything done considering work schedule and the boat in storage 2 hours away.

 

Thanks for all the input, I will keep everyone posted on my progress good or bad.

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As a last resort drop the lower unit and check for blocked exhaust ports from carbon build up , condition called " coking " : Had this problem on my 8 HP OMC.

Good luck and let us know how you make out !May be a good time to change the impeller.

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Bad gas? I had a Yamaha 90 act the same way on some bad ethanol gas. Now I will only run ethanol free. As soon as I drained it and refilled my issues were fixed.

Sent from my iPhone using Lake Ontario United

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Does it lose power or does the rpm drop off even at full throttle? On my old boat I had a 55 Suzuki on it and when I was under full throttle some times the rpms would drop and if I slowed and then powered up it would fix it's self. It was a stuck switch that was to power down if the motor was trimmed up to much. It got stuck up when I was trailering the boat... not sure if your motor has the same thing

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Double check the fittings on both the engine itself and the tank lines. I once had a bent prong on the engine male fitting that allowed air in and the one at the tank was a question mark as well. I know you replaced the lines themselves but it may be worth the time concentrating on those connectors

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It sure does sound like a fuel delivery issue.  Is it a tiller or remote operated motor?  If it is remote with a control box you may want to try to choke the engine when it is slowing down.  That surely will tell you if it a fuel delivery problem.  

 

Jim

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tlr462: The engine loses RPM's, and if i back off the throttle and then throttle it back up, it runs, but will eventually do it again. 

 

jimalbert: This is a tiller. 

 

Got new plugs and the carb kits but can't get to the boat until next weekend. I will keep you guys posted. Keep the ideas coming.

 

Thanks

Baytech

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Well u should still be able to Try my theory of choking it. If the motor speeds up when you choke it it's a fuel delivery issue. If it bogs down tour getting good fuel.

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I had same exact issue with my 115 efi merc It was an electronic float, basically engine was starving for fuel.

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Compression check first..... Readings should be over 115psi. Anything lower could mean carbon issue or just internals worn out.

Sent from my XT1032 using Lake Ontario United mobile app

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If readings are low, try the mercury power tune, its a decarb product. The piston rings get jammed up with carbon and don't seat inside the cylinder. Happens alot

Sent from my XT1032 using Lake Ontario United mobile app

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See if it does the same when the cowling is taken of the engine. Sometimes there is an exhaust leak under the hood. The air intake starts taking in exhaust gas,and the engine becomes oxygene starved.

Also ,pour a can of Seafoam in the tank. It is a decarbing,carburetor cleaning mixture. It may also be a carburetor float being stuck in place and not letting enough fuel through.

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Replace your tank. Had same problem, replace my tank and problem was solved. The ethonal eats at the plastic components in the pick up unit in the tank.

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Checked compression, all cylinders between 100 and 120 so I put in new plugs, and then I pulled and cleaned all three carbs. The top carb had the most gunk in it, with the bottom carb having the least. Put everything back together and she ran like a top. 

 

Thanks for all the advice and suggestions, it's what make this board great, 

 

Baytech

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Glad it all worked out for you. I thought it was a fuel issue.

Sent from my SM-G900V using Lake Ontario United mobile app

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