i have a 78 merc. 115hp outboard. i have checked compression and that is good. good fire on all cylinders. changed the spark plugs and cleaned what little corrosion off the inside of the distributor. motor runs but still runs bad and when i get the boat going it plains out then the motor just chokes out and dies. 
any suggestions would help alot. thanks.
need a little more info. is this the 6 cylinder motor? has is been sitting or is this all of a sudden? have you replaced any parts? does it idle ok or run crappy all the time? are the plugs wet or dry when it dies? is there spark right after it dies? sounds like its starving for fuel either by gummed up carbs or by a fuel line sucking air.
it has been running great until last week. i was on my way back to the landing and it started and ran good and when it plained out it just choked out and died. started it again and same thing. and yea its a 6. i haven’t replaced anything on it. i just fixed the bleeder line had a hole in it. but that didn’t help.
Was the compression check done since this started acting up? What was the compression on all the cylinders? Is your fuel bulb staying hard? You said it is choking out, is it really smoky when it starts back up or is it leaning out?
did the compression check right after it started having trouble. 125 on all cylinders. the ball does go soft. fuel pump? but that doesn’t explain why it runs bad right when i start it. doesn’t really smoke. it did the first time since i fixed the bleeder line. smoked like crazy for a few mins.
sounds like either a bad fuel pump or check valve in bulb if its starving for fuel or bad line somewhere if its pulling air. do you have a glass inline filer? you may be able to see if it pulling air or just starving…
if the ball is going soft replace it, they are around $5 (I just replaced one of mine 2 weeks ago) and try it out. let us know if that fixes it.
no i do not have a glass inline filter. the filter in internal. i will try putting a new bulb in and see if it fixes the problem. i never even thought about that being the problem. thanks guys. 
i will let you know how it goes.
do the line with the bulb and not just the bulb should have quick disconnects on each end so its quick and easy. i replace mine every spring and keep the old one in a storage compartment for an extra.
Here’s a quick check I would perform.
With the hood off, simply squeeze the bulb with one or two hands as hard as you can while you look at all fuel line connections. None should leak and if so a possible source fuel vaccuum source.
Could be an old fuel line collapsing too.
I have an 2001 Mercury Optimax – It kept cutting out on plane, it was the fuel line. The fuel line coming from the side wall – the fuel line was deteriorated on the inside housing, the debris was going into the fuel ball plugging the check values in it. Had to replace the fuel water separator, new fuel line and bulb. Motor runs awesome now.
Fuel filter? Did you put any detergents through it recently. I would also wonder about bad gas.
well i put a new bulb and hoses and still isn’t running good. i looked for a leak but just cant find one. tried squeezing the ball really hard and all that happens is it overflows the carbs and gas runs out. any other ideas? i miss the river.
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