89' 70HP Evinrude Compression questions

[scott324]

Hello all,<br /><br />I just checked the compression on my motor. It quit on me about a month ago. It hasn't been running very well for the last 6months, but I thought I fixed it by redoing the fuel lines (inproper mix ratio). I get three different readings on the cylinders.<br /><br />1 - 95-100<br />2 - 105<br />3 - 110<br /><br />I followed the directions in my manual ( adding a tbs of oil to each cylinder) and got 120 on all three.<br /><br />What is the proper compression for my motor? Can't seem to find it in the book or manual. It is the 3cyl 70HP VRO 1989.<br /><br />The book says the rings may be worn or scoring on the cyl walls. What is the best way to confirm this. Thanks for any help.<br /><br /><br />Scott

 

[ob]

Re: 89' 70HP Evinrude Compression questions

There are no specific numbers for compression.I expect your engines original numbers were somewhere in the low 130's.Numbers at or over 100 and within 10 percent is acceptible.Try performing a decarb on the engines cylinders and see if the numbers come up a bit.Could just be coked up ring grooves causing the lower numbers.<br /><br />Next thing I would do before giving it a good run is to rebuild and thoroughly clean each carburetor.

 

[scott324]

Re: 89' 70HP Evinrude Compression questions

Thx for the reply. I neglected to mention that it is not running at all right now. My manual says a compression less than 100 is bad!! I need to check for spark, but I have to wait till my wife gets home.

 

[rodbolt]

Re: 89' 70HP Evinrude Compression questions

ohhhh sounds like a plan<br /> here dear hold this while I crank the engine <br /> ohhh I love the plan.<br /> I almost did it once with the mag from an old merc. I said hey baby hold this and she did. however seeing as I had not had supper I chickened out .<br />your compression numbers while not the best are rather normal. still has enough to adaqutly burn fuel. there were some problems in your year range where the corrosion would actually move the head gasket but that usually showed up as a hot horn above 4000 rpm or so.<br /> the add oil is total BS<br /> does not prove anything with a two stroke other than we can blow oil on the wall from 20 ft.but for some reason seloc and clymer still have it in the book.<br />a spark tester will help. someplace on this board is a homade one that looks good. the spark must be capable of jumping a 7/16ths gap.<br /> I am with ob<br /> clean the carbs and decarb it well. maybe twice.<br /> or pop the cyl head off and inspect it.

 

[ob]

Re: 89' 70HP Evinrude Compression questions

Your top two holes are right on the fence.The lower numbers are not necessarily a result of cylinder wall scoring.may just be sticky rings.Was this engine propped to turn 6000 at wot when it was running well?What did you mean by improper mix ratio in your orignal post?Does this engine still have the vro in service are were you mixing at 50:1?

 

[scott324]

Re: 89' 70HP Evinrude Compression questions

Thx for the replies. The improper mix ratio referred to the fuel system sucking air. I could not get the fuel filter to fill more than half way with fuel. <br /><br />It ran ok before. Had a problem with it dieing after coming off plane and going to idle. Someone suggested it was running lean and this could be the cause. I have had the water pump replaced and stator replaced a little less than a yr ago.<br /><br />Update:<br /><br />Spark is good and got it running. The one piece of fuel like I didn't replaced had a crack. It was a real pain in the butt to get started and smoked lieke hell, but I attribute that to the oil I dumped in the cyls. retested the compression and got:<br />1 - 100<br />2 - 100<br />3 - 115*<br /><br />* This spark plug was the only one relatively clean. 1 & 2 were very cruddy. Any thoughts on this??<br /><br /><br />I also saw some globules(sp?) coming from the prop as I ran it, gray/brown. Could this be from just sitting for over a month or something else?

 

[scott324]

Re: 89' 70HP Evinrude Compression questions

Also, what is the preferred brand of decarb?

 

[ob]

Re: 89' 70HP Evinrude Compression questions

I use OMC engine tuner.Make sure the engine is warm and just follow the instructions on the can.Others use seafoam with good results.Again ,make sure your engine is propped to turn 6000 with a light load.

 

[scott324]

Re: 89' 70HP Evinrude Compression questions

OB,<br /><br />I run at ~5800 WOT with just me in the boat. Also from before the VRO is still intact.

 

[ob]

Re: 89' 70HP Evinrude Compression questions

10-4.If you plan to decarb ,give us an update on the results.

 

[scott324]

Re: 89' 70HP Evinrude Compression questions

Will do, any opinion on the oily substance comnig from behind the prop?

 

[Solittle]

Re: 89' 70HP Evinrude Compression questions

Most likely the oily substance coming from behind the prop is unburned oil from the fuel. It is usually black in color but may be dark grey or brown due to water. This is very normal.<br /><br />To be on the safe side you need to check the oil in the gearcase as it is possible that you have a leaking seal which would allow for the intrusion of water (((not good)))!! Even better change the gear oil unless you have done it in the last year or so.