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Old 08-03-2014, 19:07   #1
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Mercury 3.5 hp Outboard Woes

This nearly new 3.5hp outboard and dinghy was part of the deal when I bought my sailboat. I knew the motor had been sitting for a while (and would not start) so I took the carburetor apart and cleaned it with carb cleaner. The main jet was plugged but the carb cleaner took care of that. I reassembled everything, put in some pretty fresh gas, and cranked it up. Damn thing would not run or idle properly no matter what I did.

After doing some research, I found that many other people have had the same issues with this motor. I'm tempted to sell the damn thing on CL and buy a new Yamaha or other brand.

Before taking the carb off the motor. I documented everything so I could reassemble it in case I forgot how it all went back together.




Carb from hell looks innocent enough



opened it up to find expected varnish and ****. The main jet in the center of the pic has an opening about the size of three human hairs.



I guess the only recourse is to buy a carb kit for $60 and try that. I sure as hell don't want to spend $200 for a new carb for this POS.
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Old 08-03-2014, 19:19   #2
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Re: Mercury 3.5 hp outboard woes

I have the same motor and have never had a bit of trouble with it. The only issue is that it takes a few plus to start it when it is cold. Did you blow out all of the carb passages with compressed air? Those small idle jet passages are not easy to get open if they are clogged.
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Old 08-03-2014, 19:21   #3
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Re: Mercury 3.5 hp outboard woes

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I have the same motor and have never had a bit of trouble with it. The only issue is that it takes a few plus to start it when it is cold. Did you blow out all of the carb passages with compressed air? Those small idle jet passages are not easy to get open if they are clogged.
Yes, I'm pretty sure I did. Not having a repair manual handy was a bummer so I had to feel my way around the carb.
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Old 08-03-2014, 19:21   #4
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Re: Mercury 3.5 hp outboard woes

I will buy it shoot me a pm
Also you must use rec gas with small motors
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Old 08-03-2014, 19:22   #5
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Re: Mercury 3.5 hp outboard woes

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I will buy it shoot me a pm
Also you must use rec gas with small motors
I used regular gas. If you were local I would be really tempted to sell it to you at a good price.
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Old 08-03-2014, 19:27   #6
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Re: Mercury 3.5 hp outboard woes

You can’t just take some “Mechanic in a Can” and clean the exposed surfaces. Spend 30 minutes and remove all the parts. Even the one behind the tamper proof plug. Surgically clean and you’ll be good to go.
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Old 08-03-2014, 19:30   #7
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Re: Mercury 3.5 hp outboard woes

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You can’t just take some “Mechanic in a Can” and clean the exposed surfaces. Spend 30 minutes and remove all the parts. Even the one behind the tamper proof plug. Surgically clean and you’ll be good to go.
I'll try that next. I've owned several outboards before and never, every had this kind of trouble with one. Hell, even my old Seagull ran better than this one.
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Old 08-03-2014, 19:36   #8
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Re: Mercury 3.5 hp outboard woes

A few common issues with small outboards.

- Make sure the float actually floats! Put it in a bowl of gas by itself for a few days and see if it sinks.

-Make sure the carb gaskets are in good shape and are air tight. An air leak will make it very difficult to start & run.

- Did you change the fuel filter? If the bowl looked like that the filter is probably not letting much gas by.

Also what exactly is pretty fresh gas, I would go with some real fresh gas.

Good Luck!!!
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Old 08-03-2014, 19:37   #9
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Re: Mercury 3.5 hp outboard woes

Chuck your gas maybe your car can burn this stuff. Buy new gas without ethanol. Clean the carb with compressed air and cleaner. This may take several full cleanings. Mek works but can tear up some gaskets. I use mek but you are warned.
After a few years you may give up and find a good rowing dink.
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Old 08-03-2014, 19:39   #10
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Re: Mercury 3.5 hp outboard woes

Thanks Opie,

I think I'll order a carb kit and put new gaskets on it along with all the other suggestions and give it one more go before I dump it.

Does anyone know where the idle set screw should be set? It was all the way in when I removed the carb.
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Old 08-03-2014, 19:45   #11
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Re: Mercury 3.5 hp outboard woes

He’s got the green weenie going on. I agree with the filter thing but without a complete tear down, which is pretty simple on that engine, he won’t fix his problem.
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Old 08-03-2014, 19:53   #12
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Re: Mercury 3.5 hp outboard woes

When ya had that Sea Gull, ya had REAL gas ! These days ya have something but it's not the gas that engine needs !! Downhere in Louisiana the gas stations advertize haveing Non-Ethanol gas, in a Good engine like what ya have, that darn alkie gas makes for carb problems like what ya have ! You have to run the carb clean out of fuel when ya shut down if your useing the stuff!! Boil it out with the toxic cleaner, blow it out real well and ya should be fine!! If you can find the real gas somewhere use only that and ya should never have this problem again !
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Old 08-03-2014, 19:55   #13
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Re: Mercury 3.5 hp outboard woes

Start with a turn and a half and adjust as needed from there !
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Old 08-03-2014, 20:12   #14
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Re: Mercury 3.5 hp outboard woes

that carb idle screw is on the top not even on the carb body that's an air valve screw just lets more air in.The first picture has the idle screw in it facing us.also the screw on the bottom of the carb is a fuel drain.
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Old 08-03-2014, 20:14   #15
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Re: Mercury 3.5 hp outboard woes

I'll look for some non ethanol gas but it's not easy to find.
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