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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4728
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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I have a 1980 Mercury 140 hp outboard. It starts and runs

Customer Question

I have a 1980 Mercury 140 hp outboard. It starts and runs and idles well. The problem is when I stop for a while and restart it tends to "dog" out when I add in power. No matter how slow I add throttle it loses power and won't get to plane. If I get it to go to plane it runs fine. Sounds like it is loading up. Can't find a local mechanic that knows anything and am tired of throwing money at these idiots. "Supposedly" had carbs rebuilt, new wiring harness,.... I suspect that it is a timing or carbaration issue. The local shops only have mechs that seem to know newer ignition systems.
Submitted: 2 years ago.
Category: Boat
Expert:  Jeff G. replied 2 years ago.
Welcome,this question may need more than a single answer. Please post back with additional questions on this at any time.
That ignition system is basically the same as the V-6 Mercury so they are easy to understand.
There are a couple things that can be causing your problem.
The inline 6 motors have a tendency to run on the hot side, when you turn them off all the cooling water drains leaving the block hot. This can cause vapor lock, evaporation of fuel in the cylinders and crankcase and hard starting and jugging of the engine.
First of all make sure the carbs are syncronized. They are adjusted with the 5/16 head machine screws on the plastic linkage between the carbs. You want then to all be closed at the same time, and open at the same time.
Check the idle mixture. these engines like to idle on the rich side. Usually 2 turns out from lightly seated will be a good starting point. If you turn them in to lean the carbs too much at idle, you may get a better idle but harder to accelerate, what you are experiencing. The idle mixture screws are in the tio off to the side facing forward.
Next look at the float caps, where the fuel lines attach. You should see small brass air jets in the caps. remove and discard these jets. This will slightly richen the mixture and prevent powerhead damage from a too lean condition at cruising.
Check your spark plugs, use NGK BUHW spark plugs. If yours are old replace them.
Now for operation. If the engine has been sitting and heat soaking then run the engine at a fast idle for a few minutes, about 1200 rpm, before accelerating. This will pull fuel through the engine and allow the block to fill with water and cool the engine. Sometimes this is all it needs.
Many times even the most highly tuned inline will hesitate.
Also check on the fuel. If you are using fuel bought in the fall or winter, even though it may be OK, it may be a winter blend and that can cause hesitation problems.
Check these things out, try operating it a little different and lets see if that gets you going.
If you don't understand something let me know.

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