Mercury will start cold, won't start hot!

SirSnuke

Recruit
Joined
Aug 13, 2009
Messages
2
I have a 2003 Mercury 115 EFI Four Stroke, which will start like a charm first thing in the morning at the boat ramp and run great to the first couple fishing destinations. But a little later in the morning after those first couple starts and stops the motor becomes progressively harder to start.
I check to make sure the primer bulb is hard.
It is getting sufficient power from the batteries, I charge them at home between each trip.
I've checked and replaced fuel filter in motor and in-line water fuel separator element. Bowl on water fuel separator has had no debris or water in it.
Checked fuel cooler water pressure for clog/debris, thinking this could be a vapor lock problem - no problem there, the water lines are clean with good flow.
Spark plugs look ok.

Once I do finally get it started, it runs fine at any RPM.
Not sure what to check next.

Anyone have any advice for someone who wants to get back out fishing, but now fears going too far from the dock?!
 

SirSnuke

Recruit
Joined
Aug 13, 2009
Messages
2
Re: Mercury will start cold, won't start hot!

Any advice out there?

Much appreciated.
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: Mercury will start cold, won't start hot!

Do you have a manual?if so I would be looking at troubleshooting EFI system first.Could also be a compression issue.Grab a gauge and check your compression,cold and then warmed up.
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Mercury will start cold, won't start hot!

Why do you have to charge the batteries every time at home?

Failure of the charging system to keep up with the electrical loads during operation will reduce cranking speed as the batteries get lower, making for more difficult starting.
 
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