half power out of 50 hp mercury

[miclea0317]

hi, hopefully i can get some good help from someone on here since the guy that supposedly fixed my engine couldnt. ive got a mercury 500 50 hp thunderbolt ignition, and it only seems to have half power. i pulled the bottom two plugs out and it didnt make a change at all in how the motor ran, so i took it to the place i got the boat and he said he adjusted the carbs, but it still runs the same, it seemed to be getting good spark when I pulled the plugs. the top two cylinders seem to be running fine,but over all the exhaust smells really rich. i hope i can fix it without spending alot of money. thanks for the help!

 

[tmcalavy]

Re: half power out of 50 hp mercury

If you pulled the plugs/wires on the bottom two cylinders and it didn't affect idle, then you may not be getting enough juice to make the bottom cylinders contribute their share. Start with the basics. Run a compression check,. you should have 90 or above in all four...dry, above 100 is good on wet test. All four compression values should be within 10 lbs. of each other. if not you have a prob with the low reading cylinder. then check spark with a spark tester. then check your wires, wire routing (each to the correct plug?), and carbs. If it smells rich when you run it, the carbs may be leaking gas...time for a rebuild or the fuel pump diaphragm may be worn out...time for a rebuild. Just be patient and you'll find the prob. if you work through it logically. what year is your 500? do you have a manual? if not , buy a Seloc...it'll teach you a lot. I have a 73, and I accidentially reversed the bottom two plug wires once....dropped the power in half, at least, but it still ran nice...luckily my boat guy only charged me $50 for a tuneup, timing and synch...but I felt real dumb anyway.

 

[miclea0317]

Re: half power out of 50 hp mercury

thanks for the help, i will try your advice. hopefully i will get some time to work on it, i will let you know how it goes. thanks

 

[12Footer]

Re: half power out of 50 hp mercury

What Tim said, and in that order.

<br /><br />Please do let us know what you found. I hate to hear these things from boat owners with newly-aquired boats. I smell a rippoff every time.<br />And the dealer should face-up to his own music.

 

[camarokid57]

Re: half power out of 50 hp mercury

I READ WHAT U SAID AND MY DAD HAS A 35 HORSE MERCURY IT HAD SORTA THE SAME PROBLEM THE MECHANIC SHOWED HIM IT NEEDED A NEW PUMP UP BULB CAUSE IT WAS PUTTING OUT TRASH TO THE FILTER IT ALSO HAD A BAD DIAPHRAM WHICH WAS FOODING THE BOTTOM CYLINDER WHICH CAUSED IT NOT TO RUN WE CLEANED THE CARB RIGHT BEFORE SO WE COULDNT FIGURE OUT WHAT WAS EXACTLY WORN. HE HAD CARRIED IT JUST BEFORE TO A PLACE AND THEY JUST WANTED TO SELL ANOTHER MOTOR BUT WE CHECKED COMPRESSION WHICH THEY SAID WAS BAD AND WE HAD 125PSI WHICH IS GOOD. WELL ANYWAY THE LAST MECHANIC WAS HONEST AND IT IS FIXED WITH THE DIAPHRAM AND THE NEW BULB.

 

[miclea0317]

Re: half power out of 50 hp mercury

thanks alot guys, i was thinking of checking the fuel pump to see if the diaphram is bad, how exactly can you tell. ive got a feeling this could be the problem, or maybe the float in the bottom carb is stuck, but more than likely its the diaphram. i appreciate any help i can get.

 

[tmcalavy]

Re: half power out of 50 hp mercury

The pump on my 73 Merc 500 is a piece of rubber and a gasket. When it's shot, gas drips from the pump housing. I replaced all the guts recently for a whopping $2.10 (boatingsolutions.com). Cost more for shipping that the parts. <br />If the float in one of your carbs is sticking, it will leak gas out the top of the carb. I put a kit in both my carbs ($18 each). Took about 30 minutes...unfortunately from 72 on forward, it takes about 2 hours to just pull enough stuff to get to the carbs. If you do that, go easy...lots of non-durable stuff in very close quarters.

 

[miclea0317]

Re: half power out of 50 hp mercury

i didnt see any gas leaking , and if a bad diaphram and a stuck float will cause gas to leak then im stuck , i dont know what it could be.

 

[tmcalavy]

Re: half power out of 50 hp mercury

Get a manual, then go through a logical diagnosis sequence that I mentioned earlier. Your carb float or fp diaphragm doesn't have to leak like mine did to be bad, that's just how mine acted. Check compression, spark, wire conditions, timing...then move on to fuel system. Oh yeah, if your fuel bulb won't stay firm, its a sign that the fpump is wearing out...or so I've gathered. Mine did that when it was worn out.

 

[jim dozier]

Re: half power out of 50 hp mercury

Squirt some premix into the bottom 2 carb throats and see if it pick up any. If its not firing because of lean fuel mixture that will let you know. You said you had good spark, yes? Do a compression check and report the numbers.

 

[Walker]

Re: half power out of 50 hp mercury

What year is your motor. The newer Mercs have different size idle jets in each carb and the lower cylinders don't do much at idle.

 

[miclea0317]

Re: half power out of 50 hp mercury

im not sure of the year, but its not very new, its looks to me as if its a early 80's. i will try what you guys have said on friday ( i will finally have a day off). oh yea, the primer bulb does stay firm. im actually hoping the bottom two plug wires got switched like someone said happened to them, that would be too nice.