1995 28hp Evinrude 2 stroke - top speed performance

[mrdopes]

Personally, I'm not too savvy with outboards, as I'm worked mostly on I/O. I've got a 95 28hp pushing an aluminum 15ft side console. Engine starts up and runs steady, never breaks down, never fails to start, but i feel like i should be getting much more speed out of it at full throttle. First couple times i took it out, with 1 other person, i was hitting around 18-20 mph at full throttle, now i am hitting 12-14 (6 months later) with the same weight on the boat. In neutral, it will rev up much higher than it will in gear at full throttle.

Today i am going to pull/check the plugs, run some seafoam through it, and see what i can figure out. I am sure it is something maintenance related, any thought or insight into what else i should take a look while i am at it?

 

[jimmbo]

When you take the plugs out for inspection, do a Compression Test. Also check to see that the spark can jump a 7/16" gap. Fuel filter? Is the fuel tank venting properly?
Revving it in neutral proves nothing, the engine is not under a load, and can result in a runaway engine.

 

[mrdopes]

@jiimmbo-

compression
spark jump at 7/16"
Fuel filter
Venting cap check

Will do! Thanks!

 

[mrdopes]

Compression was at 115 and 120
Fuel vent was not blocked
Fuel filter was not dirty, but i cleaned it anyways
Plugs were normally worn, so i changed them out
I ran a can of seaform/gallon of gas/oil through it

I would suppose the next step is another trip to the river?

 

[oldboat1]

Spark test is important to determine ignition strength. Also possible a cylinder is dropping out at higher rpm, reducing power.

The high speed jet is behind the forward-facing bolt on the bottom of the bowl. If you remove the bolt, you may be able to clear a blockage by running a soft wire or piece of stiff mono through the orifice, then flushing with carb cleaner.

 

[mrdopes]

"Spark test is important to determine ignition strength"

I've ordered a decent tester, the one i have is a cheapy.from Harbor Freight. Should be here Sunday.

 

[iggyw1]

Not a mechanic here, but I had a lot of experience with boats and motors since I was 16 yrs old and I am now 70. Just a though here. Do you have a floor in your boat with flotation foam between the floor and the hull of the boat? Might be "water logged" and adding a heck of a lot of weight to your boat.

 

[mrdopes]

"Not a mechanic here, but I had a lot of experience with boats and motors since I was 16 yrs old and I am now 70. Just a though here. Do you have a floor in your boat with flotation foam between the floor and the hull of the boat?"

Nope, no foam. I took it out today and the Seafoam treatment and changing the plugs worked wonders. I was hitting 25mph with a full load. Problem solved!

 

[iggyw1]

"Not a mechanic here, but I had a lot of experience with boats and motors since I was 16 yrs old and I am now 70. Just a though here. Do you have a floor in your boat with flotation foam between the floor and the hull of the boat?"

Nope, no foam. I took it out today and the Seafoam treatment and changing the plugs worked wonders. I was hitting 25mph with a full load. Problem solved!

Great. Good to hear the problem has been solved!