74 envinrude 115 (2 stroke) slowing lossing power and speed every year

[darth rodney]

I have a 74 Glastron Swinger 187(trihull) with a 74 Evinrude 115hp

two years ago she was crazy fast 40mph+
last year a little slower
This year she still moves maybe 30mph and thats a big maybe.

Plenty of of 50-1 fuel oil
Plug gap .030
spark test 3/8 inch+ jump
Compression on cylinders Top left 90psi bottom left 90 psi Top right 90 psi bottom right 95 psi
Pulled cleaned the put back all four idle orifices.

Changed lower unit lube this spring.

What have I missed and need to fix replace or repair?

thank you

 

[racerone]

Compression numbers are very low.---Try another guage !!

 

[Dabbler_E]

Just a thought, but it's possible that the problem is not with the motor but with the boat. If the floatation foam is getting waterlogged over time, your motor may be pushing hundreds of pounds of extra weight. Two ways to check that would be to drill a hole in the deck and poke down into the foam to make sure it is dry all the way through (sealing the hole afterwards, of course) or to take a visit to a truck scales to compare with the published weight of the hull + trailer + motor.

 

[darth rodney]

I dont know if it matters,

I was testing on a cold engine, fuel shut off, water running through the system with mickey mouse ears. .


I have searched high and low on the internet, and have not found OEM psi. I saw in a forum a person was quoting 130psi in the same engine.

Do you have a reference sight for chronologically enhanced Evinrudes?

If my math is correct dry weigh of the boat, engine and trailer is 2,305lbs

 

[emdsapmgr]

I'd think that engine should have had at least 125 lbs compression when new. Yours is getting low. More than the normal 10% variance from new. So, it's low. Likely it's getting tired and that's what you are seeing. You might want to pull the heads for a visual inspection of the cyl liners/pistons.

 

[darth rodney]

emdsapmgr ,

Dabbler_E

racerone

Thanks for all your help.
Looks like I will be doing my first marine engine rebuild this winter.

 

[BigB9000]

I was doing a compression test on a 60HP once, it got 90PSI via starter turning.
I then hooked it up to a 200amp Engine starter.
That engine spun so fast!

Anywho, compression numbers jumped to 125.

So is 90 that bad?