1978 Evinrude 115 hp

[JimbC]

I have a ? I am working on a 115 hp Evinrude for a friend. I put brand new plugs in today ran it for about 15 mins. The 2 plugs on left side facing the motor from rear are black and wet the right side plugs are wet but not black. Is this the evidence of a bad carbon build up?

 

[racerone]

Just post the results of a compression test.

 

[JimbC]

125, 125, 122,115

 

[racerone]

You might want to remove the 4 bypass covers to inspect pistons / rings.-----Just 6 screws each and some $ 2 gaskets required.

 

[JimbC]

And What is this going to do for me? I am just wondering if I should just do some seafoam to try and clean it up.

 

[racerone]

Sure , go ahead with the " mechanic in a can " route.

 

[Chinewalker]

Was this on a hose or in the water, under load? Motors tend to run cooler on a hose, and don't burn as cleanly.

 

[JimbC]

On a hose. the 2 right plugs look to be normal for that short run time, but those two left were really black and the wet fuel/oil mix made it look like black oil. I'll take a pic of them and post.

 

[emdsapmgr]

Likely the black, sooty plugs are firing. That's a pretty normal appearance after this engine idles. The two wet, clean ones may not be. You can do a simple test. Swap the two power packs. Run the engine. See if the plug appearances change between the two heads.

 

[JimbC]

Well I did a spark test and they all are jumping a 7/16 gap would probably jump more if I made it wider. The plugs were hot as well when I removed them wouldn't that mean they are firing. The top pic is the left side plugs the bottom is the right side. Note how much cleaner the bottom pic plugs are after 15 mins of run time.

 

[emdsapmgr]

I'd probably put a laser temp gun on both heads. It's possible you have a problem with one of the thermostats. It is possible that one of the two is stuck open, causing the two plugs on that side to run cold at idle. When that happens, you can have differences in plug appearances. You'll want them both to come up to normal temps so that you have "normal" combustion. Cold-running cyls then to accumulate carbon over the long haul. (Not good) If you do pull the stat housing apart, best to just replace both stats and make sure the two pinholes in the plastic valve body are both visually clear/open.

 

[JimbC]

Yep I was noticing the water not pumping out of the left port hole as it does on the right. I just told him yesterday we needed to put new thermostats.
So the ones that are very black are the ones on the cooler side?

 

[JimbC]

We took it to the lake the other day and it would not get up on plane/no power. So I have cleaned and rebuilt the carbs The bottom carb was leaking from gaskets as well. Got the new plugs and have only ran on the hose for about 15 mins. Hopefully that was the problem Like said about comp. was 125 to 115 seems it should get up and go with those comp #

 

[JimbC]

Well no answer ?

 

[emdsapmgr]

125 lbs is the compression when the engine shipped from the factory. The 115 cyl is low. It's getting close to being 10% low-the point at which it's suggested that you delve into if for more serious problems. Still, with those strong compression numbers, the engine should run and run well. After cleaning the carbs, they should provide fuel to run the engine, yet it appears to be bogging. That could still be an ignition problem. Keep in mind that weak ignition components tend to fail once the engine heats up to normal operating temps. So-the engine will run fine when it's cold. Also, it will run fine on the trailer in the back yard when only firing on 2 or 3 cyls. You can't tell the diff sitting on the trailer in the back yard. The boat needs to be under load to check spark. Such as armed up and floating in the lake-in forward gear.

 

[JimbC]

Thanks emdsapmgr, yea I knew that. But I am getting spark to the plugs all jumping 7/16ths gap easily. The trip to lake was before I rebuilt the carbs. I guess I need to pull the plugs and see that they are firing as well. Haven't tried it under load since I cleaned and rebuilt carbs yet. I know how they run fine on hose and under load is whole different story. Also I haven't rechecked the comp since I rebuilt the carbs as I know the two clean plug cylinders were not wet like the other two before the carb rebuilds. Now that I am seeing that those plugs/cylinders are getting fuel now maybe the comp has come up a bit.(hopefully) Also The tach is stuck on 7000 is the tach bad or is that telling me something else. When I turn the key on the tach will lower a tiny bit.

 

[emdsapmgr]

The tach gets it's signal from the charging coils on the stator. (separate from the ignition side of the stator.) When the rectifier quits working, it quits re-charging the battery and also quits sending a signal to the tach. This is more likely the problem than a bad tach.

 

[JimbC]

Thanks emdsapmgr for your responses.