1995 Mariner 75 hp...WOT 3000 rpms

[tmiller4090]

After several years of not owning a boat,my boys are at the age that they wanted me to get one and I agreed with them...soooo i found a 1995 key west 1720 sportsman with a 1995 mariner 75hp....i went and looked at it it looked very clean and was about what i wanted so i took it out on the lake and ran it hard for 30 min or so....could use a bigger motor but it was adequate for what i need and was a reasonable price compared to other boats i was considering...and it ran great.Next i checked the foot for water and found none...checked compression 120-125 psi on all 3 cylinders...awesome...I bought the boat and hauled it home...The next weekend I took it out just to learn a little more about the way it handled and how it started with the engine cold,I wanted to do this before i took an 11 and 5 yr old so if there was any problems it wouldnt be a big deal.So i stop at the gas station and put 10 gal of 93 octane non ethonol gas in it..the boat fires right up and idles beautifully,so i ease out out of the cove and hit the throttle,the boat came up on plane and is running just as when i tested it....for about a minute...the the rpms fall to 3000 and will not go above that with a load on it still idles and starts fine and the engine runs smooth...I am taking the boat monday to have the impeller replaced and i guess ill have them try to figure out what the problem is then unless i can before then..the only thing i did to it was added some gas...any ideas what my problem might be?

 

[old evin]

did you mix 2 cycle oil in with your gas.you have a 2 cycle outboard

 

[tmiller4090]

Its oil injection...Thanks

 

[roscoe]

Could be a simple as a loose plug wire, or a bad coil that quits working when it gets hot.
Or a loose/broken wire anywhere under the cowl.

 

[Barramundi NQ]

Or maybe the tank had a ton of water in it and the filter and fuel lines quit and bogged you down? my 2 Cents

 

[MH Hawker]

Dont know if it apply but i had the same problem with one of the 2 stage stage ing systems , the switch box was bad on the high stage.

 

[tmiller4090]

Ok thanks guys...this gives me a few things to check...

 

[tmiller4090]

Update...had a mechanic take a look at it and he determined it to be a carb problem...he rebuilt the carbs and told me the middle one had a lot of trash in it and that was where my problem was coming from...took the boat out and it ran great for about 30 minutes or so..then just as i came across another boats wake and hit the other side...bwaaaaaah back to 3900 rpm max....i checked spark all good but could tell that the problem was still on the middle cylinder because if i removed that plug wire the was no change in the way it ran....called up the mechanic and he said to remove the drain plug in the middle carb and pump gas through it ( said all the trash usually ends up in the middle carb)and also recommended to add some seafoam to my fuel....i have done both as well as replaced the fuel filters.planning on taking it out again tomorrow and seeing how it does....any other suggestions or does this seem like the correct approach? Thanks!!! Troy

 

[roscoe]

Seems reasonable.
But if it happens again, it is time to clean out the fuel tank, possibly replace all fuel lines if they are breaking down.
Perhaps install a large external fuel/water separator filter.

 

[tmiller4090]

Took the boat out today are ran like a top....Thanks for your advice! Troy