Mercury Classic 50, No Plane Off and Carb. Leakage

[Bryan0129]

Motor: 1987 Mercury Classic 50<br />Serial Number: ? (Can't Read)<br /><br />Problem: <br /> Motor will start at with throttle up and not in gear. and then you can back it down and it will have a rough idle. Motor will start up and move along, though really slow and sounds very sluggish and not to full potential. When you have the motor fully trimmed up or down and prime the fuel bulb and solid stream of gas will come straight out of the top carb. like shooting a water gun. Does not appear to be doing it when while running. Top carb. is sucking in air, though the bottom was not. Took them apart and bottom carb. was clogged. Both floats on carbs, respond properly when air pressure was present in fuel line by air compressor. Now the motor runs fine out of water, sounds like a champ; though once a load is present on the prop, it goes back to the same old sluggish it was.<br /> Cannot seem to find a diagram online of the carb. setup for the motor without Serial Number.<br /> Any help or suggestions will be greatly appricated...

 

[Laddies]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

The last year Merc made a 4 cyl. motor they called a classic 50 was 1985, but tune up spec. were all about the same, if you need a serial number they started at 6586624 that year and a couple of numbers and that should get your inf.

 

[jonah 65]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

theres a carb diagram in the clymer manual,i've got the same engine, and had to strip the carbs,clean and fit new gaskets, also fitted a new diaphram in the pump, runs fine now.2 carbs on mine idle mix set about 1.5 turns out.

 

[jonah 65]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

tune up spec.<br />max. advance= 30 deg. b.t.d.c.@5000revs<br />throttle prim. pickup= 7-9 deg.b.t.d.c<br />throttle sec. pickup @ max stop (30 deg.btdc.)<br />full throttle revs = 5000-5500 rpm<br />idle rpm = 550-600 rpm(5deg. atdc) in for. gear<br />hope this helps - jonah.

 

[Bryan0129]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Thanks for all the responses!<br /><br />Carbs are sync.<br />Timing sits at -0- at TDC on cyl. # 1. Knowing that this has variable timing as throttle increases, what it the proper way to advance or retard the timing.<br /><br />Been working on it all day. Will rev to max with no load on prop (Out of water, or in neutral). Will also rev to max in Reverse. Though when you go put it in foward it starts to go and then just runs really slow, will not plane off.<br /><br />I am not just about the speed on this boat, but with getting passed by a huge house boat like you were sitting still only having a old beater 40 like my grandfather had is embrassing. So it is by far not about the speed, just drving around decently.<br /><br />I have a lake just behind the lake I have access of putting the boat in, though I am out of ideas.<br /><br />What is the normal size prop for this boat. 15' Evinrude Mustang, No more than 3 people on at a time. Not worried about towing anything. It has a quiksilver A5 13 degree 3 blade prop.<br /><br />Any more suggestions, I would be happy to put it in the lake and try it out again.

 

[danie]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Any expert advice on the mentioned maximum revving out of water or in neutral.<br />Isnt that a no no??<br />D

 

[jonah 65]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

yeh, i agree with damdan, i'm no expert, but i don't think you should be running it out the water at high revs-i hope your using a test tank, or muffs to cool the engine and not wreck the impeller.the timing automatically advances as the throttle is pushed forward or back until it reachs a stop (top adjustable screw on side of engine)via a pushrod.clams cannino did a great article on how to synchronize the timing a couple of weeks back, give it a look at. not sure about prop sizing, but i think it could mean 13 splines, not 13 deg.can you borrow a finer pitch prop to try?

 

[MURX]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Revving an outboard motor to redline unloaded out of the water is ludicrous. put down the tools, and back way from the victim. your problem is probally float level and a bad switch box.<br /><br />Guys, if you really don't know what you're doing pay a certified Mercury technician to do a diagnosis. it would cost you at most an hours labor, and most will be able to diagnose the problem based on symptoms<br /><br /> never rev an unloaded motor past<br />2000 RPM never! there is absolutely no reason to<br />do So

 

[Yepblaze]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Sounds to me like it's not running on all cylinders.<br /><br /><br />You might try removing the spark plugs for inspection, spark, and compression testing.<br /><br />If the carbs leak, or overflow it means they need service.

 

[PatrickIN]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Bryon......I had a similar problem with my 1987 60hp...same symptons as you. Had the motor checked out and it had valve damage.

 

[MURX]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

Originally posted by PatrickIN:<br /> Bryon......I had a similar problem with my 1987 60hp...same symptons as you. Had the motor checked out and it had valve damage.

You Boys best put down the tools......... and back away from the victims

 

[Moody Blue]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

"Will rev to max with no load on prop (Out of water, or in neutral)"<br />Unless you intend to do a complete teardown and rebuild with all new parts I would suggest you don't do that anymore <br /><br />"Had the motor checked out and it had valve damage."<br />Valve damage huh ? Would that be the intake or exhaust valves ?

 

[fishingdan]

Re: Mercury Classic 50, No Plane Off and Carb. Leakage

I have a 1985 50hp merc that my family has owned since it was new. The symptons were identical to your engine. First the carbs needed a rebuild. They were full of gunk from not being wintered properly. Then the switch box needed to be replaced. The mechanic showed me that the engine was only running on 3 cylinders unless you tapped the switch box with the handle of a screwdriver. I am glad I took it to a mechanic. It now runs like new again. Being able to rev in neutral doesn't prove anything.