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  Outboard Engine Cranks Slowly At First

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Author Topic:   Outboard Engine Cranks Slowly At First
gwenker posted 07-09-2015 05:05 PM ET (US)   Profile for gwenker   Send Email to gwenker  
I have a 2004, Mercury 60-HP Bigfoot on a Boston Whaler Sport 15. When I put the boat in for the first time each day, I lower the tilt-trim to put the motor down, then turn the key, and the motor barely turns over, like the battery is weak, almost dead. I turn the key about four more times, and then the motor will eventually fire right up like nothing is wrong. I go out on the lake, and each time the motor will start fine. It is just the initial time, after putting the motor down. It has a new, fully-charged battery. Are there some corroded cables somewhere that have a bad connection after running the trim of the motor? Where shall I look? The connections at the battery are clean. Thanks.
jimh posted 07-09-2015 11:35 PM ET (US)     Profile for jimh  Send Email to jimh     
There are many places in the engine cranking circuit that can cause problems. I wrote a detailed article analyzing the possible points of failure. There are about 50 locations. See

ELECTRIC STARTING CIRCUITS
http://continuouswave.com/whaler/reference/electricStart.html

There are really three components in this system:

--the source of power; the battery

--the circuitry connecting the battery to the load

--the load; the cranking motor

Generally my advice to anyone who is having a problem with a system that is powered by a battery is: check the battery first.

The wiring could be at fault, too. See my article mentioned above.

The cranking motor could be faulty, too.

Because this problem seems to remedy itself, I am using that as a key to my analysis. A battery is not like to become stronger the more you use it. (That might occur if the temperature were really really cold, say around 0-degree-F, but not at boating temperatures.) That tends to rule out the battery.

The wiring is not likely to self-repair, although there could be a bad connection that has resistance. Once current starts flowing the connection can get better. There is a phenomenon called wetting current where the flow of current across a connection can restore the connection. On that basis, the wiring might be suspect.

The cranking motor seems like a prime suspect. Typically there are some brushes in the motor. The brushes may be dirty and make poor contact. Once the motor starts to spin over, the action of the spinning might be wiping the dirt off the brushes, making the motor run better.

gwenker posted 07-10-2015 02:17 PM ET (US)     Profile for gwenker  Send Email to gwenker     
OK, thanks a lot. I'll look there.
jimh posted 07-10-2015 09:33 PM ET (US)     Profile for jimh  Send Email to jimh     
Where? I gave you a lot of places to look!

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