140 hp evinrude 1984

I just bought this motor on a whim compression was all over the place like 115 on 2 cylinders then 85 on 1 and one 125 whats the chance this motor need a good decarb it runs great at high rpm but at idle sputters and dies plus the boat has sat for a while.boat is trashed floor gone 1977 challenger i got it cheap really just wanted the trailer and the motor anyway.so seafoam will it loosen a stuck ring.how should i tackle this.

Re: 140 hp evinrude 1984

Running a can of Bombardier Engine Tuner through the engine may help the compression somewhat. Probably not enough to cure the low cylinder at 85 lbs. Probably best to pull the low compression head off and check to see if the compression seal ring is shot on the head gasket. Might be an easy fix (head gasket only.) That engine when new probably had well over 125 on all 4 cyls. Cylinders usually are condemned if there is a 10% difference between all 4. It is not unusual to see a compression variance of 5 lbs from one head to the other, due to manufacturing differences. When you have the head off, visually check the low compression piston carefully to see if the outer ring is still in one piece.

Re: 140 hp evinrude 1984

can you explain the compreesion ring your talking about i assume your talking about a piston ring?thanks for info this sight is great

Re: 140 hp evinrude 1984

Typically, the crossflow pistons have some significant clearance inside the cylinders. Usually you can roll them from side to side and peer down the side of the piston to see the silver ring just below the crown. With a pencil flashlight you should be able to see if the top ring is intact all the way around the piston. If the ring is gone, you may also see dents in the crown of the piston and the firing face of the head surface. Hopefully no dents!

Re: 140 hp evinrude 1984

ok thanks will let you know soon what i find