Mercury 110, 9.8 hp issues

The great help I received from you all helped me to get my 79 Evinrude 25hp running like a champ. Now my brother wants me to take a look at his Merc 9.8 hp. The model number on the cowl is 110. My first issue is that I can't find what the year of the motor is. I've tried looking it up in boats.com and just doing a general google search, but I've had no luck. Here's what I've got so far: I'm pretty sure its an 80's model motor. The decal on the side says Mercury 110, 9.8 hp. The s/n of the motor is 4127365. This motor used to be my Dad's, and my brother got it when he bought the boat from my dad. My brother said it stopped working so he had it in his garage for a couple of years. 2 years ago I borrowed the motor for a fishing trip up north and I was able to get it running, idling and shifting in and out of gear just fine. The motor runs great at idle and you can rev it up very nicely in neutral. When I took it out for the first time (2 years ago) it pushed the little boat across the lake pretty fast. By the second trip, when you throttle up, it just bogs down and doesn't produce much power. It still runs, and it doesn't really backfire or anything, it just sounds bogged down. I haven't even started on it yet, but I figured I'll need to clean the carb etc... It already has new plugs. Any other ideas? Thanks guys!

PikeSlayer, found your model/serial number over at Marineengine.com, shows to be a 1975 model.

Had a similar situation with a friends Merc '66 6hp. Went thru carb. Ran great in a barrel for a little while, then started acting up again.(Acted like it was running in 1 cyl.) After sitting for a bit would run great again for a bit then would do the same thing again. Bogging down, then surging. Ran a few more times trying to figure out. Then noticed some bubbling at a bolt near the carb. side of the crankcase. Shot the area with WD-40while running, motor killed. Leaky gasket. Just a tought......

BB, how did you find that? I can put in the s/n range of my motor under model 110 for merc, and it shows some parts, but no year. Also, that website doesn't show a carb rebuild kit. It just has some of the gaskets for mounting etc... I'm not sure but it looks like the carb and fuel pump are part of the same unit on these motors. My guess is that I will want to do both just to be sure.
Thanks for the heads up bassin. I'll keep that in mind once I get the parts I need to get her running. I don't foresee much trouble getting it going, its going to be making it develop power under a load. That is great advice!

PikeSlayer, Start at Marineengine.com>Boat Engine Parts>Outboard Motor Parts>Mercury Outboard Parts>Mercury Serial Number Guide>View Mercury Outboard Motor Models. This will open a new page, go down the page find your HP and starting Ser# for the year.

Thanks BB! You're dead on, its a 75. I took a look at the carb on the motor and also the parts breakdown on the parts site. It looks like the carb and fuel pump are more or less part of the same unit. I'm guessing my best bet is to just start with that. I can get a carb kit and fuel pump diaphragm kit for a total of about $20. I don't know a lot about these motors, but I'm wondering if the diaphragm in the pump can get hard or dry rot when its old so that it won't move fuel as effectively. Could that cause the motor to not carry a load? It revs up good in neutral, it just won't hold wide open when in gear. I'm trying to figure out if I'm on the right path or not.

I've seen motors (not outboards) have similar symptoms to what your describing but it wasn't fuel related. It was spark related. I would start out by installing new plugs and checking the plug wires. I'm not saying it can't be fuel related, just what I've experienced in the past.

JMichael said:

I've seen motors (not outboards) have similar symptoms to what your describing but it wasn't fuel related. It was spark related. I would start out by installing new plugs and checking the plug wires. I'm not saying it can't be fuel related, just what I've experienced in the past.

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The last time I ran the motor (2 years ago) I put a new plug in it when I was attempting to fix it while on vacation. The plug is pretty much brand new. I'm not sure how else to check spark without knowing what value to ring out the wires etc... I've done the plug to the motor, pull it through and check for thick blue spark, which I have. Is there another/better way to check spark intensity?

I'm not familiar at all with the diaphragm pumps. Could a stiff or leaking diaphragm cause the engine to run good when not under a load but bog down when in use?

My guess based on what you have told us (you brother had been using it and he told you it stopped working, then it sat for a couple of years, then you got it going, it ran across the lake good one time then started acting like it was down on power or bogging down but seems to idle fine) would be that you are dropping a cylinder when it heats up. I would check to see if you have a coil that is working off and on, IE when it warms up it dies. You could just try the motor in a barrel, let it run for a little bit then pull one plug wire to see if it dies, if not try the other, but it would be better to have it running on the boat in the lake under load where you can get it up to temp. You mentioned putting in a new plug a couple of years ago, was that just One new plug, if so, why just one? Keep us posted

They do make a spark tester but going by your description, it sounds like you've got good spark. Of course it could be due to a changing spark condition like bbstacker is describing or something similar.

Just an update. I finally got the motor out and started it right up after about 10 pulls with the bulb primed. It runs smoothly and idles well. I ran it up hard in neutral and then revved it up a bit in gear too. The only issue I can see in its current configuration is that the plunger style connection of the fuel line to the motor was leaking a bit at first. I flipped it 180 and it didn't leak anymore. I have a carb gasket kit and a fuel pump diaphragm and gasket kit that I plan to do this week. The plugs are both brand new. Aside from the kits and maybe a new fuel connection, I'm not sure what else I should do.

Best way to fix a merc,is to trade it in for a Evinrude or Johnson,problem solved(lol)

I'd laugh at that but I have an Evinrude 25hp that is doing something very similar to this. I have that running in a different thread if you have any suggestions. As for this merc, it belongs to my brother. He let me borrow it a while back and now he could use it on his boat if I can get it running well for him. I would appreciate any constructive observations.

New diaphragm for the pump and new seals for the carb after cleaning. Everything is installed again and ready to run up as soon as I get a chance. Problem is, I won't really know if it's fixed for sure until I strap it to a boat and give 'er.....

Someone already suggested checking the plug wires. I had a similar problem with an old dirtbike I had, reved good with no load, but wouldnt under load while riding. I noticed while riding at dusk that the spark was jumping off the plug wire to the cylinder head. Maybe try wrapping the wire in electrical tape or something to see if it fixes the problem, i it works, buy a new wire. I spent a lot of time messing with other stuff before I figured it out because the wire looked fine, when it really wasnt.

As far as what Mike said, I dont have much experiance with outboards, but my merc 20 is a p.i.t.a to work on and seems to be designed by Germans or something. They do look nice though...

PikeSlayer said:

I'd laugh at that but I have an Evinrude 25hp that is doing something very similar to this. I have that running in a different thread if you have any suggestions. As for this merc, it belongs to my brother. He let me borrow it a while back and now he could use it on his boat if I can get it running well for him. I would appreciate any constructive observations.

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???
Are you talking about your thread you started 8 years ago on the 1979 25?
The one you said you finally figured out that there was a large piece of cowling foam stuck in the throttle blade after three pages of posts by folks trying to help?

How did we warp from 2012 to 2020?