1981 or 1982 Mercury Outboard throttle failure

[mrklean]

Hey guys,

Edit: 1981 or 1982 not sure on serial, 50hp mercury outboard with thunderbolt ignition

Just got done gutting and re-doing my interior on my 1975 Lund 16ft. Looks awesome, took'er out today and it ran awesome... for about 10 minutes. Wide open great. Then we brought it back to idle and opened her up again. Nothing. Slightly higher idle. Thats it. Checked the linkages and the throttle movement. Worked and moved seemingly fine. Tried moving the throttle by hand. It'll go lower, but not any higher. All the way open no change. All the way and the motor will idle lower until death.

Tried pumping the primer ball to give it more fuel and no change. Was firm. Carbs did not leak etc etc.

Any ideas here? I feel it may be a timing issue.

I'll trouble shoot some other things tomorrow when I get a chance (spark to all cylinders, spark plugs, etc etc) Just felt it's such an odd out of nowhere issue that someone may have an idea.

Also is there a online manual for this engine anywhere out there? Much appreciated.

Serial number 5533141.

 

[1nebel0]

Re: 1981 or 1982 Mercury Outboard throttle failure

That sounds like a stator however I would verify spark on all cylinders. You don't mention horsepower or number of cylinders...Download CDI tests for trigger, stator and switch box however without the number of cylinders not sure what you have...

 

[Chris1956]

Re: 1981 or 1982 Mercury Outboard throttle failure

You might post HP and year of motor. Take a compression test. See if you have spark to all cylinders. Report results

 

[mrklean]

Re: 1981 or 1982 Mercury Outboard throttle failure

Whoops, sorry. Late night last night. 1981 or 1982 Mercury 50hp thunderbolt. Will check spark in a few hours.

 

[mrklean]

Re: 1981 or 1982 Mercury Outboard throttle failure

Update: Went out and started to look things over. Cylinder #3 is not getting any spark, the rest are very strong... (my arm felt it...) Pretty obvious why... One of the wires that run to the coils is corroded right through. It broke when I touched it... The odd thing is that the corrosion runs all the way up the wire as well (even where there was rubber insulation. Pics show.

Would this cause my throttle issues or am I just finding multiple problems here?

Also is it worth tracking down a new cable for this engine or can I just make a new one with some simple wire and connections?

 

[carholme]

Re: 1981 or 1982 Mercury Outboard throttle failure

Your s/n comes up as:

50 50 Classic 4-cyl 5531630 5531629 1980 USA

From here:

Mercury 2-takt, 4-cyl, 40 - 85 hp, produktions?r, modellguide

Parts List:

45/50 H.P. - Mercury, Mercruiser, Force, etc. Parts Lookup

Service Manual P/N: 90-86135--5

90-86135--5 | eBay

In the parts list see the internal harness, item 18 under ELECTRIC COMPONENTS:

96277A4 HARNESS ASSY | eBay

Or depending how handy you are , you could build your own or repair it depending on condition. They were notorious for corrosion problems.

Gerry

 

[mrklean]

Re: 1981 or 1982 Mercury Outboard throttle failure

Thanks Carholme for the details. Opens up a lot of information for me

The wire that was corroded to all hell was the wires running to the stator. I ran a new wire from the stator to the switchbox and got #3 spark back. Thats a good sign. Sprayed some Sea foam into each carb and motor bogged down with both carbs. Good sign. Pulled wires and got idle change good sign. I haven't gotten it out in the water to see if I actually get throttle from the motor but tweaking the throttle directly on the carbs a bit gives me a change in rpms and it revs. Also now that I understand how things work more, I was pulling on the spark advance arm before. Which would make sense why it's die when pulling it back.

Now the only issue is that I have a high idle that wasn't there before this whole throttle issue. If I pull back on the spark advance arm a bit I can get it back to the point where it seemingly idled before, but thats about a 1/8 - 3/16" gap from the arm. I don't think that could magically change, or could it?

 

[carholme]

Re: 1981 or 1982 Mercury Outboard throttle failure

The green you see in the wires is the corrosion and if one is like that, you probably have it through many of them.

Here is a link to the condensed version of the Clymer manual to help your with adjustments. Download it soonest to your computer as the link is short lived.

Small Engine Repair Reference Center Home: MERCURY - MERCURY FOUR-CYLINDER MODELS (1969-1989).

Gerry

 

[brnschoneck]

Re: 1981 or 1982 Mercury Outboard throttle failure

u may wanna look at ur fuel pumps as well they will cause it to bogg at least sooner than later ???

 

[mrklean]

Re: 1981 or 1982 Mercury Outboard throttle failure

Hey guys, thought I'd report back. Thanks for the helpful information. All led to my discovery of what is all wrong with the motor.

We'll go in order of discovery...

1. Cylinder 3 had no spark. Poked around and found that the wire from the stator to the switchbox was corroded to the point of basically no continuity. Cut it an inch or so from the stator (only place where the wire was still good) and ran a new wire with a new connector on it to the switch box, cylinder 3 has spark again.

2. Noticed that I have a corrosion forming on my main harness near the starter. Looking into ordering a new harness soon, (too pricey for me to replace at this time)

3. Noticed that my "plate-throttle" i.e. plate that pushes the throttle on the carbs had a broken tab... Found that the tab had a threaded screw hole in it. Found the other half, glued them back together and added a new screw. Works great. Ordered a new one as I don't trust the glue to that extent. The design of this plate seems kind of silly. The throttle closed half of the plate uses a plastic face to push on the throttle, most likely never to break. But, the throttle open half of the plate uses a 1/2 by 1/2 rounded tab with a 2" long screw threaded through it to push on the throttle. Lots of torque on that plastic. Surprised it didn't break much sooner. Who knows.

Finally, to respond to brnschoneck, I had the boat out twice last year only, and one of the times I could not get it to stay in WOT without pumping the ball. (pointing to bad fuel pumps) I didn't have the time, nor the need for the boat at the moment so I winterized it and went on with my life for the winter. Fast foward to this year and I have no issue with it now. I'm curious if they were just dirty and running fuel through them and running them dry cleaned them up. If it ain't broke don't fix it... I'm sure I'll deal with them soon enough though.

Now time to see if I can fix/solder a Minn Kota Power Drive control board back together that got fried a few years ago thanks to weeds and not paying attention... (Looks to be a melted connection on the board, nothing else looks fried.)

 

[BossMaverick1]

Re: 1981 or 1982 Mercury Outboard throttle failure

It must be the season for broken throttle plates. Let me guess, part number 66778T?

Yup, it happened to me a few days ago on my '84 50 hp Merc. I found the broken piece but not the screw. I ordered new parts and didn't even bother trying to glue it (although it did cross my mind).

 

[mrklean]

Re: 1981 or 1982 Mercury Outboard throttle failure

It must be the season for broken throttle plates. Let me guess, part number 66778T?

Yup, it happened to me a few days ago on my '84 50 hp Merc. I found the broken piece but not the screw. I ordered new parts and didn't even bother trying to glue it (although it did cross my mind).

Hah no **** eh? My glues held well, scored it with a razor blade and super glued it, I went out for 2 hours today tubing with lots of throttle actuating and nothing came loose

Also really funny, I found the broken piece and not the screw too. Had to do some digging through my collection to find a replacement.