motor issues

[fshrmn330]

Ok so I've got a 85 115 mariner. When I first got the boat it had been sitting for a good while and the fuel pump was bad. I replaced it and took it out. It would idle great but as soon as I put it in gear it would die. Took it home and replaced the fuel lines, bulb, and plugs.
Now it will idle great and even Rev up great sitting in the driveway on the water hose but when I put in the water it still idles great and doesn't die when in gear but it just won't take off like it should. It'll get up to about 20 mph and starts missing like crazy. Im stumped. Whats the difference on the hose and in the water? Any help would be geatly appreciated. BTW I also did a compression check and it's 100 psi on all 6 cylinders.
Thanks

 

[porthos33]

I had a broken reed on mine and it would only go about 7mph until it was fixed. Probably not your problem since it sounds like yours is all fuel related. I'm sure someone here will be able to help

 

[Oldman]

try cleaning the carbs.

 

[jims3000]

did you check to see if all cylinders had spark.

 

[south599]

Should probably rebuild the carbs too finish the system. Could also have an air leak. I redid all my fuel system and had issues like yours. Ended up being a hairline crack in the upper part of my intake tube for the gas tank

 

[275prostratos]

sounds like you are getting water in the bottom cylinder thru the bottom powerhead exhaust gasket, pull the bottom sparkplug as soon as you take it out of the water and see if its milky looking. could also be carbs need rebuilt also . the reason the boat does it in water and not on waterhose in driveway is, the boat has back pressure on while in the water and not in driveway. if its carbs dirty next time out hit the choke while trying to get on plane , motor should pick up rpm if not im betting in bad powerhead base gasket

 

[fshrmn330]

Thanks for all the tips. I have cleaned the carbs once but then ran some seafoam through it so I guess maybe it could've pulled some more gunk into them. I'm gonna check the spark of all the cylinders and check for water in the fuel. I'll report back with what I find.

 

[wrechin2]

That has the dual switch boxes just like the V6 has so all the sames issues apply. It could be dropping cylinders. It could be as mentioned before getting water into the cylinders. That has a inner exhaust plate that is notorious for leaking so check all cylinders for water. Once it starts to miss turn it off immediately then check plugs. If you don't find it i will be at the chic boat ramp this week if you want to bring it and i will look at it real quick and see if what it could be. Givee a ring tomorrow night or Monday.