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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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Have a 240hp Mercury EFI engine with Jet drive. Starts great

Customer Question

Have a 240hp Mercury EFI engine with Jet drive. Starts great cold will not start hot. Turns over like it will start but as soon as it catches it stops. Jim
Submitted: 2 years ago.
Category: Boat
Expert:  Charles replied 2 years ago.
Hello, my name is***** you for allowing me to assist you today.
Would you please post the serial number of the engine?
Customer: replied 2 years ago.
Hi Charles, Do not have the engine serial number as I am nowhere near the boat which is in a marina. Let me look at home to see if its in any of my documentation. Jim
Expert:  Charles replied 2 years ago.
Sounds good Jim. I am online until midnight CST.
Customer: replied 2 years ago.
Hello Charles, I do not have the motor information. Were there multiple models? With a 2-stroke, 240hp Mercury EFI engine it was introduced in 2002 and this is a 2003. It starts right up and idles great cold, but sounds like its idling a little low for a 6 cylinder. If you punch it under a load, skiing, it spins right up so doubt its fouled plugs. The other day had it out on glass smooth water and she held 4500-5000 RPM with out a hiccup. Nice idle back to the dock, shut it off and that was it. Tried to start it and she spins, catches right away, starter pulls off flywheel, and it sounds like it shuts itself off. Motor spins, catches (motor starts) and off.
But if I wait a half an hour or so and it cools off spins up, catches (starts) and off we go. But when it catches it is idling very slowly.
And this all started at once. By that I mean it just did it one day and has continued ever since. Mechanic tried to duplicate in a shop but it just started and started and started till he gave up. Said he upped the idle a little but not apparent.
Only other thing I can mention is the system is supposed to boost the rpm a little when idling and maneuvering around a dock or at slow speed to assist with the steering and it stopped that about the same time.
One fells said it sounds like the starter arm is pulling back to soon, before it has really caught and started.
Expert:  Charles replied 2 years ago.
The serial number helps me to see which ignition system that you have. That is the biggest difference between the years.
Do you know if a compression test was done on the engine? and if so, what are the numbers?
Your idle RPM should be about 1100. Is yours above or below that when you first start, and after a good run.
When the engine dies, do the gauges 0 out as well?
For the idle boost, it is a cable attached to the bottom of the throttle linkage, you can it from the lower left side of the engine. Have a helper turn the wheel while you look at the cable and see if it is moving at all.