Any more ideas?

[mattjeanes]

My 1974 15HP Evinrude is running well on one cylinder and hardly at all on the other. The spark is strong, I've got new points, condensors and coils, I've checked the timing. Compression test gives 90psi on each cylinder. I've swapped plugs to check that they are OK. What else can I try?

 

[BF]

Re: Any more ideas?

Is the plug on the troublesome cylinder dry? Could it be an air leak somewhere (e.g. a crank seal, or on one side of the intake) that's causing the cylinder on that side to lean out (?). Is there play in the flywheel? Bad bearing leading to bad seal? I'm really just guessing here!<br /><br />Brent

 

[mattjeanes]

Re: Any more ideas?

No, the plug is just the same as the other one to look at - same slight oil film - light brown colour - looks great to me

 

[alcan]

Re: Any more ideas?

Which cyl is hitting and which one ain't.

 

[mattjeanes]

Re: Any more ideas?

Top one (flywheel)good<br />Bottom one bad

 

[ntoracn@yahoo.com]

Re: Any more ideas?

I had a similar problem with my 1976 9.9.<br /><br />Mine would foul the lower plug within several minutes of running, leaving me running on 1 cyl (the top one).<br /><br />My problem ended up being a stuck open therostat causing the bottom plug to foul because the the engine was running way to cold. The water pump directs the water to the bottom plug first then to the top plug. <br /><br />Once I changed the plug and the thermostat, my motor will run for hours without fouling either plug.<br /><br />Thats my 2 cents

 

[marinemech]

Re: Any more ideas?

bottom crank seal may be leaking these moters are known for this if you remove power head to replace lower seal also drill a 3/8 hole thur exhaust tube to releive exhaust back pressure

 

[mattjeanes]

Re: Any more ideas?

Thanks for the ideas. I don't think that it's the thermostat as it's quite new and the engine feels as warm as ever. Could be the seal - may be a while until I can get the head off and look

 

[mattjeanes]

Re: Any more ideas?

I've just stripped the powerhead down. The seals seem OK but one of the piston rings on the affected cylinder appeared to be slightly stuck. I removed both rings and found that there was quite a bit of slop between the piston and the bore (noticeably more than on the other cylinder). I'm a bit surprised that this didn't register on the compression test - is this normal?<br />Either way I guess I'm looking at a rebore!

 

[mattjeanes]

Re: Any more ideas?

An update:<br />I've done a rebore and finally put it all back together - it runs great on both cylinders. Interesting to note that the compression is only a bit higher than before (about 100) - just goes to show that the compression test does not tell all! All I need now is some decent weather to go and try it out on the water.

 

[Paul Moir]

Re: Any more ideas?

Thanks for the update Matt! Too rare we never get to know the conclusions of these threads. It's very useful for people researching similair problems to know the outcomes.<br /><br />You may find that your compression goes up a ways after the engine is broken in and the rings have seated. But I have to agree, compression does not tell all.