Mercury motor getting slower

[SkinnerDFW]

Hi and thanks for reading my post. Heres my question. I have a Mercury 125 2000 model on a 17' champion. I purchased them new. She used to run about 55 mph wot @ 5000 rpm. Each year it seems to be dropping about a thousand rpms and as of present day she will run about 49 to 50 mph. It runs and starts with ease (of course this engine never had a good idle because of the 4 to 2 system)I use this boat at least once a week but I launch right by where I fish and yes on occasions I do take her out and run her. Don't know if this has any thing to do with it but lately I have walked by my boat in the garage and heard a hissing noise. I lift up the gas cap and give it some air. Next day same thing. Is is time for a tune up or is this normal. Thanks in advance Steve.

 

[Kenny Bush]

Re: Mercury motor getting slower

I would run some decarbon through the gas tank. I would put a can of "SeaFoam" in the gas tank, and continue to run it. If you do not see any improvement in a couple of tanks of gas(with the SeaFoam in it), it may be time for a tuneup. You can get the "SeaFoam" at any NAPA store. SeaFoam "Engine Tune", I swear by it.............. Also pull your plugs and take a look at them.... See if their oily or dry. They should all be black and oily. If you see black flakes on the plug, thats carbon. Change plugs too.

 

[jim dozier]

Re: Mercury motor getting slower

Do a compression test. Warm engine, all plugs out, full throttle. Write down the numbers. Instead of putting Sea Foam in the gas buy a decarb product and run it through the engine as directed through the carb throats. Run the engine for a day and retest the compression. See if there is an improvement.

 

[Fouled Plug]

Re: Mercury motor getting slower

If you choose to decarb, Mercury's Power Tune is good stuff. Aerosol can, very easy to use. Make sure your fuel tank is venting properly, also.

 

[kingsbiship]

Re: Mercury motor getting slower

check the prop for bangs and nicks!

 

[TELMANMN]

Re: Mercury motor getting slower

I would also suggest sea foam. Also, if you only used once a week, I have always found that if you run the motor dry(disconnect the fuel till it quits) it will keep alot of carb. problems from happening. <br /> I have never fogged my carbs. in 30 plus years after I ran them dry(run till quits, with sea foam or a stabil additive in the gas) my motors have started and ran with no probs. Maybe just lucky, who knows.

 

[TELMANMN]

Re: Mercury motor getting slower

I would also suggest sea foam. Also, if you only used once a week, I have always found that if you run the motor dry(disconnect the fuel till it quits) it will keep alot of carb. problems from happening. <br /> I have never fogged my carbs. in 30 plus years after I ran them dry(run till quits, with sea foam or a stabil additive in the gas) my motors have started and ran with no probs. Maybe just lucky, who knows.