Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

[Rock Hall]

I may have posted this request for info before, but I still havent got it figured out.
I have a new Mercury 3.5HP 4-stroke outboard. The first 15-20 hrs it ran perfectly. This motor only has the internal 1/3 of a gal tank, so I carry a gallon can and fill it when it runs out. I was out crabbing a few weeks ago and it shut off. It was about due to run out of gas, so I refilled it with about a pint from the can. It was very hard to start and would only start at full choke. Then when I opened the choke it shut off. I soon found it would run fine as long as I gave it throttle. Would not idle.
I do use Stabil and Star-tron in all my gas. The gas was fairly fresh.
The first thing I did was drain the tank and the carb, go buy fresh gas and refill. No change.
Then I added some SeaFoam to the gas and ran it for about 30 min. This seemed to help just a little.
I went to the dealer this week to check on a carb kit so I could take the carb apart and clean it. They suggested I use Mercury Power Tune. They told me to remove the carb bowl drain screw and fill the carb with the stuff and let it sit for an hour. I filled the carb from the bowl and the intake. I let it sit for about an hour, drained it from the bowl and started the engine. pretty much the same thing. It will (rarely) idle for maybe 10 sec, then shut off. Seems to run fine at 2000RPM or better. but as soon as you let off the throttle, it shuts off unless you have it choked.
I guess the next step is to remove the carb and take it apart. The full carb kit is $50 and I dont know how much the gasket kit is, but they have neither in stock.
I bought this motor to replace my unreliable 25hp thinking a new motor would be as reliable as I could get. I'm really regretting it.
Any help or suggestions or comments will be appretiated.
Thanks in advance.

 

[TOHATSU GURU]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

Since you have a three year warranty and the engine has to be less than three years old since they haven't been out for three years yet, why don't you let your local dealer find the problem?

 

[Rock Hall]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

Thats probably my next move. It just seems that every time I take something for warranty, they find that whatever the problem was, isnt covered. So I end up paying a bill. I also was hoping to use it this year and that probably wont happen if I take it to the dealer.
Thanks for the reply and it looks like thats all thats left to do.

 

[mexican]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

I have the same problem with the same engine. Bought it last year. If you come out with anything let me know. Might try calling Mecury.

 

[patjr34]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

I know this is an old thread, but I'm having the same issue with a motor I bought last summer. It's now just out of warranty. I've taken the carb apart and soaked it in carb cleaner overnight and still no luck. Anybody else sovle this yet? I'd love to know. Fyi - a local mechanc said that ethanol will gum up the low idle jet and can make it impossible to clean. That just doesn't sound right to me.

 

[ejk]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

I am having fuel problems with my 3.5hp Merc as well. It was bought in 2008 and has less than 10 hours on it. The origional owner did not winterize it properly, and a gunked up carb is my #1 suspect right now. Called Mercury - problem is not under warrenty. They also informed me that the fuel filter is actually INSIDE the carb. An inline filter would have been cheaper to make and easier to change! Mercury suggested using their QUICKLEEN product to fix the problem. I bought this engine at the beginning of the summer to use on my 12ft boat when I go camping. $800 later and I am still using the oars. Has anyone had any success in solving this problem?

 

[TOHATSU GURU]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

There is no filter inside of the carburetor and a filter would not help in this situation. What you have is old evaporated or partially evaporated fuel in the carb that has stopped up the jets. The only way to fix it is to correctly clean the carburetor. The only way to prevent it from happening again is to run the gas out of the carb after use or drain the carb after use and do not use fuel over 30 days old. Also, ethanol does not gum up anything. Water in the ethanol(from using old or crappy fuel) combined with evaporation is the issue.

 

[joecool35]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

had the same problem and had to drain the tank by taking the gas line off under the tank. when you do this you will see a little gas left in the tank in the front make sure you get it out also. then run the motor until it runs all the gas out of the carb. To do this you will crank it and it will run until it shuts off, but then you need to try to crank it and sometimes it will run just a little more. I found if I do this and put new gas into it then it will run OK. If this won't work then its some carb cleaner added to the gas. And it this don't work then its to the shop for carb work. Mercury should be ashamed about this motor it sounds like its got a rod knockin. Have a 115 4stroke yahama and it runs with less nosie than the merc 3.5

 

[bcalfee]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

I am not sure if this is still going:

I have one of these and have cleaned the carborator several times: taken the thing apart, removed various throats, etc and cleaned them all with Carb cleaner. It always runs better... but never perfectly.

The one thing I can't get to is the Pilot, which is covered by a tamper proof plug. How do I get that out?

 

[arhodes_84]

Re: Mercury 3.5hp 4-stroke New, Wont Idle. Help!!

heres what i have gathered from all of you guys on this thread. i have the same motor and having all the same problems. heres what i did to fix the problem. you guys all said that you would have to put the choke on at idle in order for the motor to run. well that means the motor is starving for fuel and wants to die. so when you put the choke on you are forcing the carb to put more draw on the fuel tank to get the fuel. i think because the carb doesnt have enough draw by itself to get enough fuel to idle. so what i did to get more fuel flow to the carb with less restriction, i took out the fuel shutoff valve and inside the bigger fuel line there is a fuel filter that actually attached to the shutoff valve, mine came off in the line so i had to do a little fishing, but got it out. then i took the small fuel line and inserted it in the larger fuel line and the clamp holds the smaller line in place perfectly. i started right up and it idled perfectly. you may have to adjust your idle screw now because its getting the appropriate fuel now to run. i am going to go to the auto parts store and get a cheapo high flow fuel filter to insert in line on the bigger line so i can change it out easily. let me know guys if this works for you and i hope this helps out.