Help my 75 HP Mercury

fashon1

Cadet
Joined
May 31, 2004
Messages
7
Ok, Guys I need help.<br />My 1984 75hp Merc. will not rev past 2500 rpm, it bogs then just about dies out. This ONLY happens when the boat is under load in the water.<br />When connected to a hose it runs well. It does not over heat and there is a consistant stream of water from the discharge.<br />I have been trying to correct this problem most of the summer with no luck. <br />I have repaired /replaced the following parts one at a time and after each change have tried the boat in the water and have seen no improvment.<br />1)Sea Foam gas additive, then new fuel.<br />2)New carb floats (adj. to 11/16)and needles/seats<br />3)Fuel line and primer bulb<br />4)Fuel pump diaphram<br />5)Completly Drained all gas from tank. <br /> Inspected the inside of the tank and replaced<br /> with new fuel.<br />At this point someone suggested that the high speed Stator could be bad, I have not replaced it yet.<br /><br />Lastly, when I did get it to run for a short time, It ran up to 5000-5200 rpm and then the RPM's fell to about 4400 RPM. It felt like a car would when the trans. shifted gears.( very strange ).I would back off the throttle a little and then give more throttle and it would increase RPM and stay at 5000-5200 RPM until I backed off.<br /> <br /><br />Please help, Im about to give up.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
14,026
Re: Help my 75 HP Mercury

Do you have spark at all four cylinders? You might check all the wires to the switch box for intermitent shorts/opens. Perhaps the shorts/opens occurs when the linkages move the tigger.
 

Elmer Fudge

Lieutenant Commander
Joined
Aug 25, 2003
Messages
1,881
Re: Help my 75 HP Mercury

you might want to check for any loose wiring or corrosion.
 

fashon1

Cadet
Joined
May 31, 2004
Messages
7
Re: Help my 75 HP Mercury

No loose wires, and I do have spark on all four cylinders. I will try to move the linkage and then check for spark or shorts.<br /><br />Thanks very much.
 

fashon1

Cadet
Joined
May 31, 2004
Messages
7
Re: Help my 75 HP Mercury

Ok guys any other ideas. I have checked for spark while moving the linkage and have spark on all four cylinders...It runs great on the hose but is still bogging just about dies abovt 2500 rmp when in the water under load..Could it be a ignition problem,since when it does run to about wot the rpm's drop quickly to about 4400 ?
 

fashon1

Cadet
Joined
May 31, 2004
Messages
7
Re: Help my 75 HP Mercury

I think so, I have blown in the vent and it is clear. I have tried another fuel tank and have the same problems. I'm at the end of my rope on this one. I think my swich box is going bad, but could that also cause the motor to bog down also ?
 

Elmer Fudge

Lieutenant Commander
Joined
Aug 25, 2003
Messages
1,881
Re: Help my 75 HP Mercury

check all fuel lines from thr tank to the carbs make sure that they're strapped real tight.<br />When the motor bogs down, does the primer bulb go soft?<br />If the switchbox was bad,i don't think that the motor would start.
 
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