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Old 11-03-2009, 05:55 AM   #1
chefdude
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Unhappy Mercury 500 - 50 HP Issues

  • I have a Mercury 500 - 50 hp that starts and runs beautiful.............but doesn' always power the boat correctly. When we get her to the water she always starts and runs good at the dock. We always warm her up good and shove off, put her into forward gear and accelerate and she dies. She starts right back up and then will do it over and over again. Sometimes she does this and sometimes she doesn't. Sometimes she does this irritation for a while and then you can hear a change in her rev pattern then she will be ready to go. Saturday she ran in forward gear as long as we didn't accelerate after putting her into forward gear but just putted along. Other times like Sunday I took her to the willy and headed out up the river after warming her up for about 30 minutes, headed out and she did the same thing. I went from boon bridge to champoeg park, turned around and headed back and half way back she did the same thing. I switched gas tanks to my spare and she started right back up and ran good again.
  1. How firm is the fuel primer bulb to be when it is pumped up?
  2. Sometimes when priming, the bulb goes flat and takes moment to plump back out.
  3. Does the primer bulb go softer after the gas is flowing when the motor is running?
  4. One time in the yard, the motor was up and the fuel from the motor filled the transom trough. Is this bad, or will the fuel leak out when the motor is up?
  5. What about fuel pump. Could this be the problem?
  • new fuel line & bulb
  • ran 3 gallons of fuel with Seafoam through it
  • thought the choke might be sticking, but it doesn't seem to be that
  • always utilize premium gas - fresh gas, usually run tanks out each time she runs good, so get new gas each time.
  • fuel tank is clean, no water, chunks or floaties
  • looked at fuel filters last night and it has the older metal mesh kind. Mercury book says to use the newer plastic filter. I might replace these, but not sure that I need to, there was no guck or clogging that I could visibly see.
Any suggestions?

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Old 11-03-2009, 06:11 AM   #2
veilside180sx
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Default Re: Mercury 500 - 50 HP Issues

Sounds like a fuel pump issue to me. Very little fuel required at idle, but under load you are dying.
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Old 11-03-2009, 03:32 PM   #3
chefdude
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Default Re: Mercury 500 - 50 HP Issues

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Originally Posted by veilside180sx View Post
Sounds like a fuel pump issue to me. Very little fuel required at idle, but under load you are dying.
I will find out soon if it was a fuel pump. Got a kit today and installed it in the boat this afternoon. I will take it out for a spin tomorrow afternoon. Had a couple little hickups when installing it, but I believe that I did a good enough job. There is this little inny and outy thing in the middle. I got them backwards the first try. Took them out and put them back in what seemed to be correctly and it started and ran for a while here in the back yard.

Thank God for kicker motors to save us from our problems!!!
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Old 11-04-2009, 04:59 AM   #4
Smj
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Default Re: Mercury 500 - 50 HP Issues

That was you with the "New to you" older boat wasn't it? Alcohol may have taken it's toll. All the rubber may have turned to mush....All fuel lines are suspect, primer bulb, hoses to and around carbs carrying fuel and crancase pulses. Fuel lines can start to shred from the inside causing an intermitent flow. Filters need to be changed, water seperator/fuel filter should be installed, bet you don't have one of those. Float needles in the carbs may be the type with rubber tips and have turned to mush.

Reread, "new bulb/fuel line".....Pieces or just the gummy residue may have fouled carbs coupled with old rubber tipped needles.

Fuel puddling in splashwell sounds like a bad vent on the tank, warmth causes expansion, bad tank vent causes pressure to push fuel past carb needles. Bad vent would also restrict flow when throttling up.

Using premium fuel is a waste of your money, your motor may not even run as well on "premium" as it would on regular. Premium, high octane, would only be used on a modified engine with higher compression to keep it from preignition, pinging.

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Old 11-04-2009, 09:32 AM   #5
budnate
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Default Re: Mercury 500 - 50 HP Issues

if this is still doing this, you will find the wiring from the stator to the coil is falty, the wiring fails inside the insulation on mercs and litterly turns to dust, what is happening as you throttle up it advances the timing and breaks the wireing and you lose spark.

replace the wires from the stator base to the coil it should go again like new.

B.
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Old 11-04-2009, 06:16 PM   #6
chefdude
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Default Re: Mercury 500 - 50 HP Issues

Quote:
Originally Posted by budnate View Post
if this is still doing this, you will find the wiring from the stator to the coil is falty, the wiring fails inside the insulation on mercs and litterly turns to dust, what is happening as you throttle up it advances the timing and breaks the wireing and you lose spark.

replace the wires from the stator base to the coil it should go again like new.

B.
Interesting. Stators are a couple hundred bucks or more. Can you replace just the wire, or does one have to replace the complete thing?
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Old 11-04-2009, 08:28 PM   #7
chefdude
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Default Re: Mercury 500 - 50 HP Issues

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Originally Posted by chefdude View Post
Interesting. Stators are a couple hundred bucks or more. Can you replace just the wire, or does one have to replace the complete thing?
I found in my book tonight how to check them without removing them from the unit. Will need to find an ohm meter to do the checking.
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Old 11-05-2009, 12:51 PM   #8
budnate
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Default Re: Mercury 500 - 50 HP Issues

cut the wire back around 3" from the stator and pray its decent enough to get ahold of some wire/dust, install new wire. very common problem with mercs from the 70's and 80's some kind of chemical reaction is what I was told.

peace, B.
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Old 11-05-2009, 04:25 PM   #9
chefdude
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Default Re: Mercury 500 - 50 HP Issues

Quote:
Originally Posted by budnate View Post
cut the wire back around 3" from the stator and pray its decent enough to get ahold of some wire/dust, install new wire. very common problem with mercs from the 70's and 80's some kind of chemical reaction is what I was told.

peace, B.
I might have found a loose connection where it connects to the rectifer. I will replace the leads. I have tested the leads with an Ohm Meter and they seem to be working when a connection is made. Not sure that this is everything wron with the motor, but a start.
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Old 11-06-2009, 03:19 PM   #10
budnate
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Default Re: Mercury 500 - 50 HP Issues

fixed?
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Old 11-06-2009, 05:55 PM   #11
chefdude
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Default Re: Mercury 500 - 50 HP Issues

Quote:
Originally Posted by budnate View Post
fixed?
Not sure yet. Will try to take it out in between rain showers tomorrow.
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