04 75hp merc won't idle/run cold

[gamewarden3006]

Ok I have a 2004 75hp mercury outboard. This motor does not like cold weather at all. Took it out last weekend (air temp low 40's) and the motor would not run by itself when cold. I have to keep pushing in the key to choke it every 5 seconds or so. This goes on for 10 minutes or so. After 5 minutes or so I reved it up to 3,000 rpm or so and it still won't run without constant choke assist. After 10 minutes or so I got tired of waiting and opened her up. I was doing 5,000 rpm on plane and it would still die if I didn't hit the choke every 5-7 seconds.

After 10 -15 minutes though the motor is fine for the rest of the day and runs like a champ.

I had the same problem at the end of last winter but just dismissed it to bad gas or something cause I ran it all spring long just fine.

I changed the fuel filter over the summer and have ran about a tank through the new one. The bulb seems fine cause even after setting for 2 weeks or more I never have to pump it more than 2-3 times to prime it fully.

Any thoughts on what I can check or adjust myself?
Thanks for any help!!

 

[CharlieB]

Re: 04 75hp merc won't idle/run cold

Is that fuel filter a WATER SEPERATING filter?

How old was the fuel in the tank, is it a sealed tank (portable) or permenant mounted tank in the boat with a vent? How much fuel was left in the tank?

Air space in a vented tank will allow the alcohol in the fuel to absorb water from the air until the alcohol becomes fully saturated with water.

Portable sealed tanks (IF you close the vent when not in use) can prolong the shelf life of your fuel and prevent many water problems.

Saturated alcohol/water seperation from the gasoline can become an issue until the tank is agitated enough to re-mix the fuel during use, BUT........ the fuel is already questionable, once parked it will shortly seperate/settle out again.

OR

your carb floats could be set just a hair to low and the engine is just slightly lean until warmed up fully.

Pull a fuel sample into a clear container, leave it sit still for 30 minutes and see it there is any 'layering' of the alcohol/fuel separating. If so, then get it used up or drain it out and replace it with fresh fuel. If using it, do not run extended WOT as the motor may be running a hair lean, it really is best to burn this stuff in your lawn mower, but who's grass is still growing at this time of the year?

 

[gamewarden3006]

Re: 04 75hp merc won't idle/run cold

The filter is not a fuel water separator type. The tank is a permanently mounted tank. I put about a half a tank into it that morning. the other half had been sitting in there for a month or so but I had put Sta-bil in it (for what it is worth).

I will check the carb floats tomm afternoon. Hopefully that is all it is. Just kinda odd how it only does it when cold though.

 

[Texasmark]

Re: 04 75hp merc won't idle/run cold

2 things I have had with my '02 90 2 cycle which is the same engine as your 75 mostly.

1. Thermal problem in a pulse pack.

Put the COLD engine on muffs at home. The easiest way to do this test is to slide a short piece (1.5") of suitable diameter solid wire along the insulation of the sparkplug wire and push it under the boot at the plug until it contacts the metal cap connected to the plug (you can feel it when it hits it), leaving the boot in place on the plug just like it is normally.

Doing this will allow you to take a screwdriver and touch the end to an exposed piece of engine metal (non painted screw ok if screwed into the block) and bring the shank up next to the wire for testing. Also with the spark plug wire hooked to the spark plug, you get normal loading on the pulse pack and it increases your ability to locate the bad pack.

Crank the engine (maybe 2 people will be needed to keep it running and do the testing) and do the test. On a good pack you should draw a nice blue (snappy) arc when the screwdriver shank is approximately 1/4" from the end of the test wire.

Your problem pack will fail to arc or if it does arc it will be weak, yellowish in color, or require a shorter gap as compared to a good pack. iboats probably has them, otherwise they are available on the www at a cost of less than $100 each.

2. This could also be a thermostat missing or stuck open but when you said that you had this problem at WOT It doesn't sound like that type of a problem. At rpm's above about 2500, or significant forward boat speeds, water pressure opens the coolant bypass valve(bypassing the thermostat) that allows full flow of ambient water through the engine and a cold engine is usually not sensitive to temp in the higher rpm's.

My problem was just the opposite of yours, it overheated at slow speeds and cooled off at the higher engine speeds where the bypass valve opened. My thermostat was stuck shut. Totally different problem occurring at a different time than my pulse pack problem.

With all that said, I still find this Merc of mine to be cold natured for the first couple of minutes of operation (the colder obviously the longer it takes). I attribute that to lean design caused by EPA regulations.

HTH

Mark