1974 Mercury 50hp Problems while under load

[zaccornell]

I have a 1974 mercury 50hp outboard on a 15 ft ranger. When I purchased this boat 3 months ago, I took it out on lake and it ran really good except for a slight miss on the high end.

I ended up restoring this boat, and had a local marine mechanic do the engine work for me.

This is what has been done:
New timing belt (which he set off of wrong mark and took a week to realize)
Put back together the control body which the previous owner took apart
Install new steering cable
New plugs

I get the boat back, runs great on muffs, but as soon as you put into load while under load it sounds and runs like dog crap. I am only able to go 5-10mph at best, rpms are no where near high enough (guessing 1500-2500 at best!) At idle speeds it wants to stall, its hard to get started where it wont stall unless i through up the high speed throttle control and let it run high rpms for around 20 seconds, with the throttle fully open it cuts out so i have to back off of it.

Took it back and he installed high speed stator which did nothing, checked carbs or so he said and that did nothing. Im sure he messed with some other crap also...After having my boat for 6 weeks and not being able to find the problem, I said screw this and took it elsewhere.

So this new shop said it was only running on 2 cylinders so they put a rebuild kit on top carb and he said the bottom carb bowl(if that sounds right) had all kinds of gunk in it. So he cleaned it up and he said he was confident that would solve the problem. WRONG...

Runs great on muffs, but hardly any better under load in lake.

What the heck is going on here? Am I not getting enough fuel? Too much fuel?

Does this engine have set screws to adjust air/fuel mixture?

How do I go apart pulling the carbs, is there a step by step procedure somewhere?

Maybe he didnt link and sync? bad needle valve? bad float? I dont know!

Compression/spark was all fine by the way, according to both shops.

The other thing I noticed is that while its moving in water it creates like 3 ft waves, but its as if im dragging an anchor back there!


*Does anyone have a link for an online service manual for my engine? id like to start troubleshooting myself and save some moola.


Thanks!

 

[Mi duckdown]

Re: 1974 Mercury 50hp Problems while under load

If I were you. I would buy An OEM MERC manual, from Mercury, or off ebay. for that Motor. You will need serial number off that motor to find one.

 

[sdeck]

Re: 1974 Mercury 50hp Problems while under load

I had same issue. the connection between the top and bottom carb throttle linkages (black plastic rod with a couple of circles in it) had slipped out of the lower carb during the install. would only throttle the top carb

 

[pnoguy]

Re: 1974 Mercury 50hp Problems while under load

I had a similar issue, and it turned out to be electrical, not fuel related. Try removing the orange and brown wires from the starboard side of your switch box. These are the "tilt" and "ignition off" wires that tell your engine to quit. I had an intermittent short in the orange wire, and as soon as I removed it, the thing ran like a top. Might not help, but worth a try. Only problem is, your motor won't quit when you turn off the key. You'll have to touch the post with the orange wire.

 

[merc850]

Re: 1974 Mercury 50hp Problems while under load

Some engines have these carb tops with a filter inside the fuel line fitting if so you have to remove the elbows to access the filter, I had poor performance issues 'cause one filter was plugged with "fur". I pulled both filters out and tossed them - motor runs fine.
There might be different carbs on your motor that have top caps that cover the filters if so open them up and clean the filters.
I think that that year motor has a distributor so there is only one switchbox.