Bad news on compression test

[crazy charlie]

I was about to rebuild the carbs on my 84 115 evinrude and I wanted to do a compression test first.Well I found out some bad news--110 in the first 3 cyls and on the last one the gage did not pass 40.i did it 3 times to be sure.I am so disappointed,I take care of my motor like no one I know.The best 2 cycle oil,I never beat on the motor,I always flush it.I cant understand how this could happen.One day it just stopped idleing smoothly as soon as i started it.What do I do now,I am not capable of repair. Charlie

 

[Dhadley]

Re: Bad news on compression test

Lets pull that head and take a peek. Might as well pull both whiler youre there. A decarb might help but thats a bumch as far as difference goes.<br /><br />If its on the starboard side that may be easy to diaginose. Tell us which one is down.<br /><br />If you were concerned about dirty carbs, that may explain the cause.

 

[crazy charlie]

Re: Bad news on compression test

Thanks for the reply,The carbs are dripping a bit so i thought the rough idle was that.The bad cyl is starboard(driver side) lower one.I guess I am capable of taking off the head. charlie

 

[Dhadley]

Re: Bad news on compression test

I hope all we find is a sever case of coking and perhaps a burned head gasket. Check it out and let us know. <br /><br />Tell us more about your set up and decarb schedule. What kind of top rpm with an average load, water pressure etc.<br /><br />Good luck!

 

[crazy charlie]

Re: Bad news on compression test

What is coking??? The motor is on a 17ft Mako,the water pressure is great usually 13-18 I think,great stream out of the pisser,great spray out of exhaust,never runs warm to hot,Cruises 39 - 4800 rpm with plenty to go if i wanted to.I have had the motor 3 seasons and have just recently(yesterday tried any type of decarb.1 can of seafoam deepcreep sprayed into carbs and some into cyls.I dont think I really did it thorough enough.I never travel with more than 1 passenger.I never tow a tube or ski.The boat has had it easy and the comp. was perfect in all cyls when i got it. Charlie

 

[Dhadley]

Re: Bad news on compression test

Coking is a form of carbon. Its a very sticky substance that causes the rings to stick in the groove and then the piston rocks excessively from lack of support. The rings stick on the "backside" and the gap end will stick out. As the piston rocks wore and worse, the gap end will eventually get broken off. Usually to the right side of the locating pin. It happens on the starboard side first.<br /><br />What is the top rpm with an average load? What grade fuel? What oil? Which spark plugs?

 

[crazy charlie]

Re: Bad news on compression test

Thanks for the explaination.I guess this is repairable?????The top rpm is about 5500 though i have never really nailed it,there are ngk plugs in it though i just bought a set of champion for replacement,i always run 87 octane and I use penzoil and penzoil synthetic.Hopefully this will be something i can repair,I am usually not that lucky.Charlie

 

[Dhadley]

Re: Bad news on compression test

You are in good shape except for the NGK plugs. They seem to create a tad more combustion heat compared to Champions which doesnt help the coking situation. Champions are a better choice.<br /><br />The fuel and oil are good choices. I like my crossflows to be capeable of a bit more top rpm although 5500 isnt horrible. I shoot for 5800 with an average load. If you stick at 5500 I would suggest a good decarb job at least every 35 - 40 hours. The factory calls for 50 but a little sooner wont hurt. If you get the r's up you can go a little further between jobs.<br /><br />Let us know what you find when you pull the head(s).<br /><br />Good luck!

 

[crazy charlie]

Re: Bad news on compression test

Thanks again for the reply,the rpms may well get up to 5800 but i really dont like to nail it so i am not positive.Should I try to do a decarb first???When i raise the rpms a little,It idles much better.It stalls when i shift rev to fwd. charlie

 

[crazy charlie]

Re: Bad news on compression test

??