87' Evinrude 150hp on 1987 overnighter WOT

[controlsct]

Took the new to me Overnighter out for the first run yesterday as if finally quit raining here in CT. Motor ran great and quick to get on plane with 2 guys and a full tank of fuel ( 65 gallons). the problem was it would only get to about 4100 rpm at 30 mph. I'm fine with this as I like to cruise about 27-30 anyway, but I cracked it WOT and motor would start to stumble and gain no rpms. just start to break up. back it off a little and ran great. Idles great and starts fine cold and hot. This is the original motor and I bought it from the original owner. prop the wrong pitch? ( I need to check numbers on it was dark when I got back to dock). power pack going? bad coil? fuel restriction? any ideas on where to start?

 

[VeroWing]

I would imagine that wot rpms should be around 5000 for that engine, so something is not right. Many times when boat sits for extended times, it needs to run a while to clear up and run right. I would first check condition and age of current fuel, boat bottom for smoothness, check all bilge & underdeck areas for trapped water (extra weight), and then make sure engine height is proper. Next I would make certain fuel is not being restricted along it's path from tank to engine, engine is tuned/timed up good, compression ratios are within specs, and carbs are recently rebuilt and working right. With all those things in order, then you can look at current prop size, and then adjust size (rule of thumb is adding or subtracting 1" changes rpms by 100-150 roughly) of prop.

 

[controlsct]

Thanks VeroWing, The boat did sit for the 2018 season and had about 15 gallons of gas with stabil in it. I filled it up yesterday with fresh fuel so it might just need to run it and clear it out. I replaced the fuel filter and fuel lines. bottom is clean ( just sanded and painted) and was inside stored. I have not taken the plugs out yet, That was going to be my first step to see how each cylinder is firing. I'm scared ( ha ha) to do a compression test on her, she has many hours and hoping to get it through one more season and then repower next year Other then the WOT the motor ran great and everything seemed fine. I will look at the things you mentioned and go from there. Thanks again..

 

[VeroWing]

Those older Evinrudes are pretty bulletproof and long lasting. Just very thirsty compared with newer outboards. if you have a fuel/water separator you should replace with new and pour fuel from old separator into a clear container and let it sit 10-15 minutes to see if there is water in it. Probably does if boat sat for over a year. If so you want to get that out of your fuel.

 

[steveditt]

Agree with above comments ,your fuel is most likely the problem which also sat in your carburetors not sure if you have 3 or six carburetors if they are dirty I would not fool around season just starting ,remember you cylinder lubrication is being supplied by your fuel which can cause serious lean mixture or destroy a cylinder if it doesn't receive enough oil . Certainly could be the things you listed but 15 gallons sitting in a tank that when filled is 65 that's not good the new fuel is not going to mix with that old stuff which is sitting in the bottom of the tank where your fuel pickup is . Remember its not a car engine it needs that oil .Good luck .

 

[Fishtales]

I'm going with do nothing and burn the fuel in the tank down. Add a good marine additive to the fuel when you fill the tank.

 

[Paul_A]

I would drain the fuel tank and run that old fuel through my mower.

Then fill a remote tank with a couple gallons of premix and a can of seafoam. Google how to decarb an outboard. You will clean your carbs and the combustion chambers.

If the oil mixing system, VRO, isn't disconnected, read up on how to disconnect it and premix in the tank.

 

[controlsct]

Thanks for all the help and comments, The boat is running pretty good as long as not at WOT so I think I will just run it and see if it improves. The VRO is still hooked up and I marked it with a sharpie on side of tank to make sure it was going down and it was. I changed out the water/fuel separator filter.