1987 70 HP Mercury (3 Cyl)

Hello again to everyone. Football season is over, so I finally have some time to work on my rebuild project. This motor was given to me by family, so I know its history....sort of. This is going to be a fairly long post, but I will try to make it halfway readable.

This motor sat for about three years. A buddy of mine had the exact same motor, but he blew up the powerhead after installing several new parts. He gave me the old motor to salvage. So far I have:

1. Replaced Impeller- Changed lower unit oil- Pressure tested good.
2. Replaced Poppet Valve and Thermostat
3. Replaced Stator and Trigger (off salvage motor- recently new)
4. Replaced Switch Pack (off salvage motor- Brand new)
5. New Plugs of course
6. Cleaned and Rebuilt Carbs ( DID NOT SOAK CARBS...I know, I should have)
7. New INLINE Filter- (Running fresh gas from remote tank)

Compression Test: 117-117-115

Motor did fire up, but it idles rough as hell. It will "POP" and smoke like crazy. It will fire back up, but only after pumping up the ball which gets soft during this time....which is leading me to believe I have a fuel issue. Getting good spark on all three coils.

My questions are:
A. What about the fuel pump? Do I need to rebuild or replace this thing?
B. I have read so much about setting timing, but I am confused as hell. I replaced Stator and Trigger which required pulling the flywheel, but I have no idea if I need to do something else before starting.
C. Do I need to remove carbs again and soak them to remove hidden gunk?

I feel like I have a fairly solid motor, and I am on the verge of getting this thing right. But I am sort of agrivated right now. Where should I go from this point?

Appreciate the help. GO IRISH Tomorrow night!

Re: 1987 70 HP Mercury (3 Cyl)

You probably have a water intrusion leak as is prodominantly an extenuating occurance with these engine like mine. I have been through 4 sets of baffle water cover caskets and 2 sets of plates and i,m still having issuse with firing. My advise id if you gonna have it done (Worst engine built by mercury) have it done right the first time in surface grinding the exhuast port block surface. Check all plates for warpage and hairline cracks. Check the interior componants including the crakshaft rod all bearings pistons cylinders rings and rods. I have been at mine for over 13 months and 900 dollars and still have issues. I,m replacing 3 rods and a .015 piston new old stock on the lowest cyilinder afected the most by water intrusion. I hope yours in a bit better shape but like I said everything must be gone over inspected and assured a proper fit ot forget it.

Re: 1987 70 HP Mercury (3 Cyl)

Maxz695,
Man, I sure did not need to hear this. I thought I was about done with this thing. How can I determine if I indeed have a water intrusion issue? I have never heard of this issue, but I am doing some research as soon as I type this reply. If this is indeed the case, I will be parting out this motor by next weekend.

Re: 1987 70 HP Mercury (3 Cyl)

There are several things that can couse your troubles. You should go thru all the systems one at a time double checking them. The compression numbers are within limits. When doing the fuel system check all the small balance hoses , fuel pump flow, rebuild carbs, check valves in crankcase, just to name a few. The electrical , check plugwires for correct position an bad conections in the coils, Test the stator, trigger, coils, all wire connections, and the fireing order of the motor. Disconect the saftey shut doun wire from the switchbox to eleminate any trouble that it could create. I use WD40 an spray it around all the seals, gaskets, and hoses to help find any air leaks with the motor running. The carbs should be numbered as you take them off the motor to work on them, as they have to go back on in the same location because they are diffrent from one another. A factory manul is the best for these and some others as the blocks are the same up to atleast 90hp for years 1987 to early/ mid 1990's. I have found bad check valves and balance tubes on some of the ones I have worked on. The fuel system would be the first system I would check on you motor. JMO
Oldman570

Re: 1987 70 HP Mercury (3 Cyl)

First eliminate all other reasons that the engine is coughing spitting sputtering etc. If you have checked all plugs for fire and all carbs are adjusted and working properly and the fuel pump and lines are all in good condition and securely fastened and you still have poping sputtering then I would start investigation the water intrusion theory. Remove the side exhaust water port cover exposing the exhaust baffle and remove the baffle. Inspect the plates after carefully cleaning the old gasket off th surfaces. Inspect the block for corroded areas and cracked areas. Some cracks are hairline fractures and very hard to see/ Using your fingernail usually will let you feel if there is a crack. If your very lucky the engine was never oveheated and the machined surface is not warped as well as the covers. Peer into the exhaust port holes and inspect the condition of the pistons and rings. If there is no signs of corrosion then you may be in good shape. Please post pictures of the piston condition for us to see and mabey able to guide you on the best way to go from there. Hopefully you just need to replace the gaskets and be done with it. Picture of the block looks like this View attachment 178359 View attachment 178360

Re: 1987 70 HP Mercury (3 Cyl)

I rebuilt the fuel pump and it is now the fuel system is really solid with no leaks. Money well spent.

I went ahead and pulled the exhaust plate to check for leaks into the cylinders....and i found no evidence of that happening whatsoever. It looked really good inside the motor with no signs of rust or corosion. Unfortunately, I also broke off four (4) bolts into the powerhead. Damn. I will work on getting those out and replacing the gaskets. When it Rains it Pours.

The motor started buch better, but I an still getting the loud and violent "Popping" noise during idle. I have linked to my YouTube video showing how the motor ran and sounded....before I pulled off the exhaust plate.

Old Mercury 70 missing - YouTube

Hopefully this link will work. Does Anyone have any ideas of where I can go from here? What does it sound like? lease check out my original posting to see the work that I have already done. I guess I may have to backtrack a little.

Thanks

Re: 1987 70 HP Mercury (3 Cyl)

Saw the video and the results. pull one plug wire at a time and find the cylinder causing the pop.Trace back and check the coil and trigger wires or distributor if so euipped. I have a 2 stroke 3 cylinder with a switchbox. Let me know what you have there.

Re: 1987 70 HP Mercury (3 Cyl)

Maxz695,
I have a two stroke 3 Cylinder 70 like yours. Do you really think ignition and not fuel? Good call on the pulling spark plug wires; in fact, I never even looked at the coils because I was getting good spark....damn...simple things first.

While I got you here, do you have any good ideas about removing four (4) broken bolts under the exhaust plate? Two of them are 1/2 in above the surface, and two of them are even with the surface.

Re: 1987 70 HP Mercury (3 Cyl)

Soak Soak Soak with pb Blaster. drill a small pilot hole through the center of the blot Stright through the entire screw there shoud be some room after the bolt and between the block that you should feel when it gets through but to be sure measure the drill bit and mark it in a hole without a bolt(nail polish or tape) as not to drill through the block. This will let you spray penatrating oil into the back side as well and work it,s way outward. I wouldn,t recommend an easy out as if it breaks in the bolt it,s a pain to try to get out and you can,t drill it. Heres a suggestion. Harbor freight or maybe ebay sells backwards drills that drill counter clockwise. Use the pilot hole (Drill straight as an arrow) and under drill the tap size as not to affect the threads, and the heat should free the bolt and let it come out even possibly with the drill bit while drilling it. Go undersize and work your way up but try very hard to not to have to drill it totally out for a retap. Can you post pictures of the broken bolt positions as some walls are thin between thread and open jacket and messing up would be a very bad thing. See pic in post 6 observe the thickness and thiness in some areas. You may have spark but you may also be arching to ground through a bad wire or crack in the coil. also a trigger wire could be grounding out or have a bad pick up coil. Run it at night and look for sparking in the wiring. Is that video of your engine? Woulda done wonders rather than a disrption of the symptoms.Unless the carb is that bad out of adjustment then it seems electrical to me.

Re: 1987 70 HP Mercury (3 Cyl)

More information Soaking it may take time several days. Heat helps thats what the drilling should help. Be sure to cover the exhaust ports as not to get any metal in there. First use a punch to make a center for the drill bit and keep it centered when starting the hole. Take your time and keep it straight. The first pilot hole is most impoartant to succeding with the next size drill bits. You can when half way to the bigger drill bit try to take an allen wrench and bang it into the hole and wrench it out. If the bolt gives even a little do this. Tighten it a bit losen it a bit tighten it a bit etc etc. Doing this will free the corrosion and eventually let the bolt unscrew. Patiencs is of the utmost. You get one shot per hole so take breaks in between broken bolts. The only other alternative is to have a pro over drill it and heli coil it. If it gets to the point of no return welding is the only other option. be careful. Best way is to start with a 1/8th dril bit and after the punch drill into the bolt about 3/8th of an inch to start on all 4 bolts as the drill bit may get dull. Use cutting oil or lots of pb blaster if nothing eles is available. Then use the next size up to finnish drilling the pilot holes. Like I said at about half way up to 5 /16bit try using an allen wrench, Tapper the edge with a grinder or a file to get it started into the hole and get it a few wacks to set into the bolt and try to get it moving but do not force it too much that hole can be used several times when soaked. Again Patience