8hp Johnson idles well, but stumbles under load, sometimes

[Mc Tool]

Interesting comments, Evinrude/johnson were all designed for champion spark plugs. Everyone I know, swears by them.

Oh ,Im not saying they are a bad plug ....they were all I used for a blimmin long time , just that I dont see them around any more .

 

[ArtVandaley]

Hey guys! I took the boat out today, but it was an electric only lake. However, I did poke around the engine and looked closely at the wiring. All appeared to be okay, no chafing on the conductors and the connections that I could access looked good. I want to add that when the engine began acting up last season, I too thought it could be electrical in nature, which brings a thought to mind. The climate control in my wife's Saab began giving us a hard time two years ago. It would not reliably activate the heating mode. Over time, it became apparent that the heating mode only wanted to work once things warmed up inside the car (of course). In the winter, it would only turn on as I was pulling into work after a 25 minute drive but in the summer, the heat would readily turn on. Finally, someone mentioned that perhaps, there is a hairline crack in the climate control's circuit board. And, when things warm up in the car, the circuit closes due to expansion. So, I purchased a used unit off of Ebay, and it worked directly upon installation!

Now onto the outboard. I noticed on my 2nd outing with this issue that the engine would, as noted, instantly start running properly after about ten minutes. I figured that whatever the culprit is, it begins to function once the engine warms up, in turn, warming up the item in question. After reading some of the responses here, the item that comes to mind is the power pack as it is part of the electrical system and is bolted to the block. So, I think it would be worth my time and $ to replace the power pack and see if that solves the problem. Sounds reasonable yes?

 

[Mc Tool]

There are 2 most likely possibilities , one is that there is a component that fails when it warms up , and tother is a dry joint .
Dry joints are where something is soldered onto the circuit board as below , the black stuff in the ring surrounding the joint is carbon from where the joint has been fizzing away .

These can be fixed by giving them a re-heat until they melt with a soldering iron . They are not always as obvious as the above ones and a real good look with a magnifying glass or loupe is the go .
Failing components is a bit harder . If you can be arsed using a can of instant freeze with a straw to direct the stuff onto individual components will cool the component and it starts working again ......tedious process but you can save a bunch of money ( fixed a 1$k sprayer dump valve pcb with a 30¢ temu diode ).
Anyhow ....I dunno if you can open your power pack to get at the circuit board so maybe a new one is the best option . I dont know much about your particular motor but others here do and maybe able to say " oh yeah , thats common " , but I think your on the right track .

 

[ArtVandaley]

Just an update:

So, I bought and installed a new oem power pack, and the engine is running like a champ! It's still hard to start when cold, but regardless, I'm so happy I was able to finally get this thing running properly again. This issue has plaqued me for over a year now, and I was about ready to buy another engine, but now I don't have to.

Thanks again to racerone, Mc Tool, and others for the help!

 

[Mc Tool]

Hard to start cold could be a choke issue....couple of things to check , The choke plate butterfly in the carb must be fully closed when the choke is on ....tight shut . An easy way to check if its a choke issue is to remove any silencer on the carb and place yor palm over the carb intake so as to completely block it and either you or an assistant pull on the starter cord ....it should light up after a couple of pulls .
Normally a properly primed carb with the choke fully closed ....it should at least blubber after a couple of pulls . Some 2 strokes will immediatly flood ( chainsaws are a prime example ) so if it blubbers and stops straight away its probly flooded , so set the choke to 1/2 or 3/4 closed and give it another couple of pulls and if it starts let it run for 30 odd seconds on that part choke .

 

[ArtVandaley]

Hey Mc Tool!

Let's say I first launch the boat. I will prime it and choke it. I will pull it with authority like ten times, and will not even try to start. Once I catch my breath and reattach my arm, I will pull it another five times, and it may pop. I will need to pull it another couple of times for it to actually come to life. Once hot though, no problem restarting. I was thinking about just bringing a squirt bottle with some premix in it, and just shoot a little into one of the cylinders (via the spark plug hole) and fire it up like that. Or, I could check out the choke as you describe haha!

 

[Mc Tool]

Yeah OK , what I would do is, firstly check that choke butterfly is closing , if it is, then with a cold motor , to open the carb bowl drain screw and let it drain out then squeeze the primer bulb and see just how quick the fuel starts to flow again ....the thinking being that we need to make sure that the bowl is actually filling up , just that it sounds like maybe you pulling on the cord is operating the fuel pump which is finishing the prime job . Its possible that the float valve is not fully opening or that there is a partial blockage .... which allows enough juice to run but makes the priming process slow .Another approach would be to pump the primer untill the bulb is firm and then keep pumping untill you get 2 or 3 more good squeezes ( think stress ball ) and then see how it starts.........full choke ....2 strokes like being on the verge of flooding to start . Another thing to check is that your idle mix screw is set correctly ( google says 1.25 to 1.5 turns out as a base line )