72 Johnson 20hp quit in middle of lake

[T0mmyboy]

Hey everyone, I am new to the forum and boating as well. I just got my first boat, a little 57 Crestliner aluminum runabout with a lil 72 Johnson motor. I took it out on Bighorn Canyon Lake here in Montana, and it was a blast. I was grinning like the cheshire cat and could have eaten a banana sideways. Until after about an hour the engine just quit. Wouldn't start back up again. Luckily I had oars and rowed back to the marina.

Since I have never driven a boat before I am not sure what a motor is supposed to feel like, but this thing started up like a champ, but had huge flat spots in the mid range. Like literally you had to skip the whole intermediate speed range. Then all of a sudden it just quit. 5 seconds before it died it surged a little, then kaput.

The motor was overhauled 3 years ago (have receipts and parts list) but sat for 2 years. The gas in it was bad.

Any ideas on what it could be? I'm a motorcycle guy, and in my experience 9 times out of 10 if the engine just quits out of nowhere its usually electrical. But then again it just sat for 2 years and I don't think it was winterized...so I am thinking the carb? what do you guys think?

Also how fast are these things supposed to be? The aluminum boat is only 225 lbs and the engine is 100, with me in it the boat weighs like 550 lbs. It felt fast, but GPS said I was only going 19mph.

Thank you

 

[jimmbo]

Welcome to iboats
Do you have spark? Is fuel getting to the carb? Do you still have compression? You said the fuel was bad, There may be gum/varnish in the carb and it plugged it up, actually there may be gum/varnish anywhere in the fuel system. Once you verify you have compression and spark, spray some gas-oil into the carb, if it starts then you have a fuel delivery issue. Plugged filter/screens, bad fuel pump, plugged fuel pickup in the tank. You said it surged right before it died. Leaning out, an engine will do that. Running out of gas does the same thing. Also some of the other symptoms you describe sound like a plugged up carb.
If you don't have spark, you have to pull the flywheel and inspect the ignition system. The engine may have a cracked magneto coils, bad points.

Did you replace the water pump impeller before taking it out? And verified there was oil in the gearcase?

 

[bspeth]

You can adjust the trim to plane better maybe,move some stuff around to balance your load and you might get a few more MPHs.If you are at any elevation,19 aint terrible.

 

[Scott Danforth]

welcome aboard

Jimbo covered the basics. those old johny-rudes suffered from cracked coils.

if it sat, hopefully the water pump was working

 

[racerone]

Gas and oil was mixed at 50:1 I hope.

 

[T0mmyboy]

Hey thanks guys for the pointers. I actually got a service manual for Johnson/Evinrudes off the site now and I am reading through it. I had no idea how much these engines differ from bike engines.

Well, I remembered to mix the correct oil/fuel mixture. The engine still has compression I presume because it cranks the same. No harder or no easier to yank. Just nothing happens.

I am going to start looking at the fuel pump/filter first (after making sure I have spark) and then take off the carb and clean that.

I barely had time to look at it since the incident, but I will get cracking next time I get home.

Again, thanks for all the help thusfar