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Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I'm having a problem with my 40 hp Mercury outboard turning

Customer Question

I'm having a problem with my 40 hp Mercury outboard turning up. it idles but when I go to get speed on it, it won't turn up. I was working on it with the cover off and touched one of the rubber boots on the top spark plug and received a shock. Does that mean that the spark plug wire is bad? Should I have received a shock through the rubber boot? also, I ran new fuel lines from the fuel tank and put a new squeeze ball on. I used fuel line left over from my larger boat and noticed when I was putting it together making the connnections the line was a little bigger than the plastic barb. It was a loose fit but I was satisfied after I put the hose clamp on it and clamped it down. could I be sucking air from these fittings? or is my problem electrical? PLEASE HELP!
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello Kurt. My name is Tan.

The boot should not shock you. The fuel lines are sucking air. If the fuel line doesn't fit tight to the connections there is no clamp you can use to get it tight enough to keep air out. Now this may not be your only issue.

Has the engine been sitting unused for awhile?

When you run the boat squeeze the primer bulb when engine is acting up. Does it run better?

Post back with questions and findings.

Customer: replied 1 year ago.
I've squeezed the ball and makes a little bit of a difference. I just bought the boat but believe it might have been sitting. It was running good for a while. Had mechanic go over it and he said settings were all off (not sure what that means). He put new plugs and tuned it but I should have had him rebuild carb but said he wouldn't know til I ran it. It was running well with wrong size fuel line for a while.
Expert:  Tan replied 1 year ago.

Squeezing the primer bulb usually indicates a fuel delivery issue. This can air or a fuel restriction or failing fuel pump. The way to find out which is to run the engine on an auxiliary fuel source. This will tell us if it is the boat side fuel system or the engine. If it still acts up and squeezing the primer bulb helps the fuel pump is the cause of the problem. If engine runs better then we know you have a restriction or and air leak. The restriction can be debris in the fuel tank clogging the fuel supply or an air leak which we know is possibly the fuel line connections.

The is no reason for setting to be off unless someone has been messing with the settings they don't go out of adjustment. Now what I have seen inexperienced mechanics start playing with adjustments trying to get engine running better wrong they don't cause engine performance issue. It is either ignition of fuel..

One other test you can do that will tell us if it is a carburetor issue is choke the engine when it acts up. Does it run better?

Post back with questions and findings.