HELP ME 50 hp mercury

[flyin_bryan84]

I have a early to mid 80's mercury 50 hp. its a inline 4 cyl. heres the problem

i bought the boat motor and trailer about 3 months ago...the guy i bought it from said there was a problem with the motor. well i took the boat out in the water and top speed was about 8 mph.

well come to find out the wires to the trigger were chewed up...replaced trigger...took boat back out no change.

checked plugs...bottom 2 cyl werent firing...traced it back to the switchbox....replaced switchbox....replaced spark plugs.

now IF i get it started( once in ten tries) it only idles in between 1200 and 2500 rpms in neutral. no forward no reverse. i cant idle down far enough to get it into gear. i have cleaned both carbs thouroughly and adjusted to factory specs.

i have also checked compression
107# 109#108# and 104#

so i have great spark, good fuel lines, carbs, and pumps.

so can anyone please tell me anything to check or fix?

thank you


bryan

 

[argiceswed]

Re: HELP ME 50 hp mercury

How is your fuel tank? is it old or new? Is the vent on the tank open?
I had similar problems the other day with my Merc 500. Turned out to be rust in the tank that cloged everything. Changed the tank and hose, cleand the fuel system and now it goes perfectly. You should also check the fuel pump.

 

[tmcalavy]

Re: HELP ME 50 hp mercury

It may need a link-n-synch, timing advance has to be synched to carbs opening when give it juice.

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

the tanks on the boat are brand new....the hoses syphon balls and connectors are all new. the fuel pump and filter have been taken off and cleaned through and through. all new fuell lines inside the motor. and new gas and oil.

any other advice please

thank you bryan

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

ive tinkered around to the timing advance and the carbs. how do you fine tune something like that?

thanks


bryan

 

[Tom P]

Re: HELP ME 50 hp mercury

Just a simple long shot. Try running the boat with the cover off. If it runs fine than the problem may be the wires arching to the metal cover. Another way is to run the motor at night and pass a screw driver (plastic handle) around the wires. If you see sparks jumping, then your wires are bad. I’d really suspect that’s the problem if everything sounds good with the muffs on and the cover off. They don’t make wires for that motor. It’s roll your own. But . . . Merc part number 84-821945A56 will fit. This drove me nuts for months and I took the same steps you did. Until I removed the cover on the water. The electric shock I got from the cover dam near knocked me out of the boat.

Good luck,

Tom

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

i dont think its an electrical problem at all...ive replaced everything from the switch back.

i think its a fuel/air problem....i just dont know where to go.

ive tinkered with the carbs, time advance and the throttle screws...adjusting minimally from one end of the spectrum to the other....

one local mechanic suggested that i have a blown powerhead...but how could that be if i have good compression on all cyl?

and other ideas are welcomed

thank you

bryan

 

[argiceswed]

Re: HELP ME 50 hp mercury

Is the timing of the distributor right?

If you take the cover of the adaptor pulley you should see a mark (an arrow, if I remember it right) on it and it should align up with one of the two lines on the flywheel (the other line should align up with the TDC mark at the same time).

On my motor I have a mark on the cover itself and it doesn?t align up with nothing. When I got the motor it started and ran like crap and I got no power out of it (didn?t rev up and very often it just died when I put it in gear).

Just by curiosity I fixed the motor. I unscrewed the cover on the distributor pulley because I wasn?t satisfied that the lines didn?t align up, saw the arrow on the pulley. Aligned one of the lines to the TDC mark and the other was by the distributor and to my amazements the timing was off by one tooth. Got it aligned, put the belt on, screwed on the cover again, started the motor and what do you know it ROARED, it SCREAMED.

Check the timing...

 

[argiceswed]

Re: HELP ME 50 hp mercury

This picture isn't good, but worth a try.

 

[ddrieck]

Re: HELP ME 50 hp mercury

Could be a bad crank seal leaking air into the system. I had a 2 stroke snowmachine engine that ran much the same as your describing. Ended up being a bad crank seal on that engine. Just a thought

 

[tmcalavy]

Re: HELP ME 50 hp mercury

Read the threads in the FAQ forum about doing the link-n-synch. If no info there, you can get a Merc tech to do it for about $50.

 

[kssmallies]

Re: HELP ME 50 hp mercury

Hi I have a 67 or 71 500 also I don't know yet which year. I dont' know much about the motor but im trying to stuff everything in because its too much money to have them looked at. Anyways bought the boat 2 weeks ago took it to lake to see if it even float and the motor started right up but would only go about 5 mph when I throttled down the motor would rev way up but would not go anyfaster so I left it idiling while I checked to see if the trolling motor worked and when I went to take of again I idiled way up and throttled down and the whole motor started to shake and the boat barely moved and then died. I could smell gas real bad I tried to start several times and then boom. Blew the whole top cowling cover off the motor I think I flooded the carb because gas was pouring from them and with all the wires showing I must have made a spark when trying to start. Anyways took it back home and waited 2 days and took it back out and she runs fine without the cover on? The boat still wont' go over 5 mph though I think I spun the hub or do you think I should check anything else. Also what is the easiest way to clean the carbs just pour some carb cleaner in with the gas? THanks

 

[tmcalavy]

Re: HELP ME 50 hp mercury

Please start your own thread, you wouldn't want someone else hijacking yours.

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

well i dont have a distributer...i have a switchbox and a trigger so the distributer alignment isnt for me.

i have a 50 hp mercury...no model 500

and where would the crank case seal be about on the motor?

any other ideas will be greatly appreciated

thank you again
bryan

 

[kssmallies]

Re: HELP ME 50 hp mercury

sorry

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

ok...im attempting the link-n-synch....and i know that i need to get the #1 cyl at top dead center....where is top dead center? when the head is its closest to the spark plug? futhest? or middle?

and when im using the timing light what am i looking for?

thank you

bryan

 

[ddennis]

Re: HELP ME 50 hp mercury

Easiest thing to do is get the manual. Well worth the money you will spend

 

[flyin_bryan84]

Re: HELP ME 50 hp mercury

i have the manual...and its too generalized for me....i have basic mechanical skills....but the manual i have covers about 8 years of mercury motors from 15 hp to 250 hp....there is too much general stuff...i need the specifics.

thank you

bryan

 

[fishingdan]

Re: HELP ME 50 hp mercury

ok...im attempting the link-n-synch....and i know that i need to get the #1 cyl at top dead center....where is top dead center? when the head is its closest to the spark plug? futhest? or middle?

and when im using the timing light what am i looking for?

thank you

bryan

- top-dead-center is the position of the piston when it is at the top of its movement (closest to the top of the cylinder).

- The timing light is basically a strobe light. You will connect it to the spark plug wire of cylinder #1. When the engine is cranking or running, shine the light at the timing mark and it should show you the timing marks while the engine is running. In other words, the timing light will flash at the time the #1 cylinder fires and show you the timing marks at that instance. Then adjust the timing as needed. Without the light, you could never tell where the timing marks are when the engine is running since everything is moving.