90hp Evinrude piston problem

[dst888]

So I bought a boat and took it out. It was running rough so I replaced fule and vacume lines. Took it back out and ran good for a while and then was falling flat when accelorating. When I got it back in one plug was badly fouled and the the piston was damaged. Cleaned the carbs and took it back out and ran good for about an hour then started running rough and falling flat. So I then pulled the head and cleaned all the carbon out and the piston (see pic). Now it runs good sometimes but stalls and there is a thump sound, kind of like a misfire. I think it is predetination.

So the question is can I get this thing to run good enuff to take out again???
Mybe a different plug in that cylender or bigger gap? Help

 

[emdsapmgr]

Re: 90hp Evinrude piston problem

Before you put any more money in it, I'd do a compression check to make sure the powerhead is worth working on. The compression should be in the 90-100 lbs range on all 4 pistons. The lowest one should be within 10% of the highest.

 

[DJ]

Re: 90hp Evinrude piston problem

A damaged piston will not heal itself. Once damaged, you're done. Further running will only cause a MAJOR failure.

 

[dst888]

Re: 90hp Evinrude piston problem

I did a compression check and all cylenders are right around 125psi.

 

[dst888]

Re: 90hp Evinrude piston problem

I did a compression check and all cylenders are right around 125.

 

[AlTn]

Re: 90hp Evinrude piston problem

at the beginning of the Forums..click on Top Secret Files..scroll down to Decarbing Motor...this may help and won't hurt...your compression isn't a problem..how did the cylinder walls look as far as scoring?...do the decarb procedure and post back results

 

[dst888]

Re: 90hp Evinrude piston problem

yea I did the decarb and also pulled the head and cleaned it out. That is what the pic is of. It's in the shop now but when I told the guy it had pitting on the piston he did not look like he wanted to touch it. We will see what he says but odds are he will say it needs rebuilt. I had it going like 35 on the water before I cleaned all the carbon and sludge out of that cylinder. Then did a compression check and the #s where great. Now just won't run right, it is making a thump out of the exhaust every once in a while. I think the carbs need adjusted and timing checked. So I will see if this guy will do that. If not a guy has a 1991 150hp force for sale at a great price. One head is off because he said he had a leaking head gasket. He has all gaskets and parts to put it back together. I am going to wait and see what the shop says about the evinrude and then maybe get this force and hope its a good deal not another pain in the A.

 

[emdsapmgr]

Re: 90hp Evinrude piston problem

The pits on the top of the head are from parts of a broken top piston ring. You should have matching dents on the underside of that head. You can visually see the ring if you move the piston slightly from the head side with the head off. Or, pull the intake side (bypass) cover and look at the piston from the side ports. If the ring is intact someone has replaced the ring. If it is missing, you are in need of an overhaul before more damage occurs.

 

[dst888]

Re: 90hp Evinrude piston problem

I looked it over pretty well and the rings looked good with a little carbon bildup between them I beleave. I fond a damaged wire under the flywheel that goes to the power pack I beleave. I spliced it together with some 18awg wire I had. I sounds great and runs great in neutral but when I put it in gear it stalls. The first thing I am going to do is fix the wires with factory ones if I can get them. If not I'm thinking use spark plug wires?? Not sure but I think you can loose spark?? Do you think this could be because of the pitted piston with 125psi of compression or a spark or carb issue?? carbs have been cleaned but I did not have the tool to adjust the floats...I only adjusted the float drop. The book said 7/8 to 1-1/8 so they are both at like 1in. This thing sounds new if its not in gear???

 

[emdsapmgr]

Re: 90hp Evinrude piston problem

Any engine will seem to run fine at idle. It could run on 2/3 cyls and sound just fine. The true test of engine condition is when the lower unit is buried 24" under water and you load the engine up by putting it in gear and throttle up hard. That's when you need all 4 cyls to start working.

 

[metriccrescentwrench]

Re: 90hp Evinrude piston problem

... and the the piston was damaged. Cleaned the carbs and took it back out and ran good for about an hour then started running rough and falling flat. ....... but stalls and there is a thump sound, kind of like a misfire.

Maybe it's just me, but I wouldn't even think about taking a boat out if I knew it had an engine with a damaged piston. Sooner or later it's going to leave you stranded.

 

[dst888]

Re: 90hp Evinrude piston problem

Thanks guys for all your help. Got her running great...FINALLY. I was ready to shell out big $$ for a new engine. There where a lot of problems with this motor sence I got it a month ago. But the icing on the cake was a damaged wire that went to the power pack. It was under the fly wheel, it was rubbing and grounding out on the fly wheel. that explains why this thing has been driving me nuts! That also explains why the plug fouled and the got damaged. So just so you know...a pitted piston will run just fine. Well for now it is...Im gonna keep my fingers crossed but I think as long as I keep my eye on it it will last till fall! And Its not like I take it out into the ocean. Just out into the Indian river Bay and Rehoboth Bay where there are a lot of other boaters.