Logo
FULL SITE MENU

1987 9.9hp....stumped

H

heckhole

Member
Here is a quick cliff notes of my problem I just can't solve. I have a 87 Mariner 9.9hp.

BEgan starting hard & leaking fuel. The enricher gasket went. Replaced enricher & motor was still hard to start and didn't seem to run up to speed anymore, but still was reliable.

Began taking 30 pulls and a spray of fuel to start. Was down on power but still ran.

Kept taking 30 pulls and a blast of fuel to start and was considerably down on power and would bog heavily at half or 3/4 throttle or more.

Completely took carb apart and cleaned. Needle was spotless, rest of carb was soaked, blown out, etc. Replaced fuel lines, replaced all vacuum lines, new plugs.

Problem didn't go away but engine starts first pull EVERY time now. Idles nice and smooth.

Ordered new gasket & diaphragm kit. Also ordered carb rebuild kit. The motor now runs a little better, but runs like a CHAMP on FULL choke. Unless it's on full choke, it will bog out.

I'm completely lost. I feel like something is out of sync with the butterfly arm and the throttle cable & arm? I noticed on the butterfly arm, the white piece that is on the throttle arm & slides when the throttle is opened, has a small adjustment in it and it looks like over time the screw & nut didn't hold tight and it has moved. So I went to play with it and voila, the nut fell off and into the lake it went.

My only concern from the carb rebuild was the float. It has a lip on one end & I didn't notice how my old one came out of the carb. Right now I have the lip end upright.
 
Last edited:
I own three small Merc's/Merc Mariners ranging from 1986 to my "new" 1991 model :)

Over the years I have seen almost everything that can "go" on them "go" at one point or another.

It sounds like you possibly had multiple problems, that when they all showed up at the same time really gave you a hard time.

There are two fairly common issues with these that could cause you to "have to keep the choke on" to keep them running.

Firstly - the upper main crank bearing (from factory) sucked on these. They leak. Not too bad at first but as the years go on, they wear out (it's a kinda metal ring, with a rubber cap that has a spring like thingy that is supposed to hold tight against the upper crankshaft where it exits the top of the crankcase, just below the flywheel.)
Anyhow, it's all one piece and the rubber wears out.

Not difficult to change - pull the flywheel, pick out the seal (Merc part 26-125671 - called "oil seal, crankcase upper", runs about $17), put in the new one and replace the flywheel.

The second recurring issue is a bad intake gasket (Merc part 27-192031 - "gasket, intake cover", about $4) - it's long and rectangular. The (sides) of the gasket are pretty narrow and if you get a backfire or a "sneeze" you tend to tear the gasket when the pressure tries to blow back into the crankcase.

The intake is located on the right hand side of the motor, near the back (if you are standing behind the motor). If you have remote controls, the linkage must be removed to even get a good look at the cover. On tiller models it's wide open to the intake cover which is held on with 3 bolts (5 minute job to change the gasket).

A tell tale of either of the above conditions being present is an oily coating all over the powerhead - or a goopy, oily mess in the lower pan of the engine cover.

So with a sluggish performing engine, if it looks like the motor has been sprayed down with fogging oil even when it hasn't, my top two culprits would be the crank seal (upper) or the intake gasket, or both...
 
Thanks a ton for that information. I realize now that I had a few problems arise at the same time that made troubleshooting a nightmare!!! I have been rebuilding and fixing 2 stroke snowmobiles for years and I've never been so defeated by an engine before!

So defeated that I gave up and sold the motor & the boat! But I know my buddy will appreciate this information and he is aware of the small issues I had with it. I will pass this along to him.

I did have a sneezing problem, it literally sounds like it sneezed. I replaced the fuel pump and did a gasket kit along with replacing all the vacuum lines at once. That was enough to get it to run better but not full throttle with no choke.

Thanks again for your response.
 
A sneeze could also be a cracked coil.

Get him to remove the coils and give them a really good wipe down, looking for very fine "hairline" cracks.

If any are found I would replace them with aftermarket coils from Sierra. They cost about 25% less than the OEM coils and produce higher voltages which really smooth out the idle on these little motors...
 
Back
Top