Need Help Identifying year of 70 Hp Evinrude and random high RPM loss (Pics)

[Stokes81]

Hey guys,
been a regular visitor here for a long time, just now decided to join since i need some help that noone can seem to help me with,
Ive been an avid boater all my life, so im fairly good when it comes to working on outboards, however this ones givin me a headache,

I have 5 boats, just bought my 6th, its a 15 ft cadorette W-hull with a 70 HP Evinrude on it, (I wanted a beater boat to use for utility / fishing etc.) however im having trouble identifying the year of the motor since it was rebuilt 2 years ago and the sticker with the numbers on it are gone and the top covers been painted over.
Im thinking its somewhere between 75 -85 but cant be sure. Il attach some pics.

I may as well tell you what im up to since im having trouble getting it to run right. motor starts perfect. runs perfect at idle although i have to give her a bit of throttle when i go into gear but after its run for about 15 min it wont stall out when going into gear.
I took her out for a test run at my marina 2 weeks ago and it ran like a dream, got up on plane in seconds, the motor didnt struggle at all.
a week after that i trailered it to a fishing trip and went to open her up and to my suprise it started to stumble when trying to get into the higher rpms and i couldnt get it to plane out (obviously). Now the funny thing is we get to the campsite and sleep the night off. the next morning i take her back out and its running perfect again.... for about half an hour. then while im cruising at high speed the motor just putters down, and starts running at low rpms again. it did this several times during the weekend. So it runs real well, when it wants to.....any ideas guys ?

heres the pics of the motor.

 

[fireman57]

It looks like it's between a 1975 and 1978 as there is no telltale on it. As for the running when it slows down do a spark check. Your coils look old. Check them for cracks. Could be one is getting hot and arcing or just cutting out.

 

[jakedaawg]

I would compression test 1st.

I would spark check when its having an issue.

I would run on a different known good portable tank and line.

I would try the primer bulb also when its haveing an issue.

As far as year goes? Does it have a primer solenoid or choke plates?

 

[flyingscott]

I am going to say 73-76 model hood looks about right for them. Has choke plates

 

[emdsapmgr]

Keep in mind that these electronic ignition systems are finicky. When one of the major components (stator, timer base, power pack) get a lot of hours/run time on them, they can weaken. When you get a weak ignition component, they tend to run just fine after they are just started. They may run fine till the engine warms up to it's "normal" operating temp. As it continues to run, the normal heat range of the engine starts to affect the weak ignition component. When it starts to break down, you'll get some sort of miss. Shut the engine down and leave it overnight to cool down, and it will start right up running fine the next am. Till the engine warms up again, then the weak part will break down again. So, once you run it and it starts to misfire, check the spark plug wires to be sure they all have strong, constant fire. I'll bet you find a problem somewhere. I'd suggest you run a compression check on the cylinders. Best to know the compression is ok before you put any $ into it.

 

[David Young]

Your motor looks just like my 1977 70 hp Evinrude.

 

[Stokes81]

Thank you all for the prompt response. Really appreciate it guys. I've checked the compression and it's 120 across the board. I have a feeling it may be the power pack however. I'm gonna run through your ideas and post again with what worked. Just in case someone has a similar issue. Love you guys

 

[oldboat1]

well, could be a fuel issue particularly if a permanent tank. Adding fresh mix to old fuel won't dilute water, of course. Jakedaawg gets at it, along with potential fuel pump issues (squeeze the primer bulb when acting up and see if there is improvement).

 

[Stokes81]

I tried priming the bulb during the issue. Doesn't seem to do anything. The bulb stays firm regardless.

 

[fireman57]

Sounds like it is a spark issue. You might have a coil that overheats and quits once it gets warmed up. When it does this do a spark test immediately. You can also use a timing light when this happens. A lot easier.

 

[jakedaawg]

The timing light will tell you if you lost spark completely. Open air.gap spark check when your having issue will show weak spark which is also not acceptable. Just my two cents, dont want to upset anyone.

 

[Stokes81]

Turns out it was a bad wire from the coil shorting out. You guys were right. It was the bottom cylinder. What was happening was that the wire was rubing against the clip that holds the motor cover down and shorting out. I still need to do some more test driving but it seems to be running perfectly. Purs like a kitten through the entire range of throttle. No hiccups like before.

 

[fireman57]

Sounds like you can now enjoy the rest of the summer. I can't tell you how many times wire have been yanked off by someone putting the cover on without checking to see if anything is in the way.

 

[oldboat1]

might run it after dark and see if there is some arcing (abrasion). I can't quite make out in your pic what is going on with the bottom coil wire -- maybe you have taped it. Might want to replace the wire, maybe the coil and wire assembly if you have to. But I would run it for a while like you suggest. It's August.