'61 40hp Evinrude Lark III won't get full power

[Postmarc]

Fairly new to iboats, but used a lot of previous post info during my project--thanks to all who share good tips.

I just finished restoring my first boat, a '57 runabout. Took it out recently and the Boat Gods are punishing me by not letting all the 40 horses run.

Motor was gone over by a mechanic after sitting for 5 years (fogged), impeller and plugs replaced, all fluids replaced. First time I took it out this fall, full power was not an issue. 3rd time, I can only get up to about 1/3 of what I could before and doesn't get up on plane. Purrs like a kitten, runs smooth, just slow. I have switched pressure tanks, switched fuel bulb lines, switched gas, and checked the throttle linkage to make sure the set screw didn't slip, all to no avail. I shot carb cleaner in while my daughter drove. Nothing. Any suggestions?

 

[bktheking]

Re: '61 40hp Evinrude Lark III won't get full power

Sitting for 5 years?

Check spark first, if spark is an issue-
Check coils for cracks, points to see if they are dirty or not adjusted properly, or everything under the flywheel may need replacing.

Carb should be removed and cleaned as well, carb is probably dirty.

We did a 64 in the summer that sat for 2 years, carb was removed and cleaned, points were cleaned and adjusted, 1 wire wasn't all the way in one of the coils. It idled nice but had no power, 1 plug wasn't firing properly and consistantly.

 

[lindy46]

Re: '61 40hp Evinrude Lark III won't get full power

Motor will idle nice on one cylinder, but I'd bet you have a bad coil cutting out when you go to WOT.

 

[kenmyfam]

Re: '61 40hp Evinrude Lark III won't get full power

Basic health check to begin with.

Compression
Spark
Fuel delivery
Spark plug condition (look for noticeable difference between them)

Go from there.

 

[Postmarc]

Re: '61 40hp Evinrude Lark III won't get full power

You know, that's what I love about this forum. Great suggestions, and only a little while after I posted.

As far as what was done before, I mentioned that the coils were pronounced good by the mechanic, carb was cleaned and new kit was installed, good compression was found in both cylinders, and spark plugs were replaced.

That's what has me scratching my head--I had full power the first couple of times out, and didn't do anything to all of a sudden go to Sunday driver cruise speed. I'll admit I am not a boat mechanic, but I am willing to use my brain and good advice to troubleshoot this.

I was trying to use process of elimination for the fuel-to-motor connection by switching tanks, switching squeeze-bulb fuel lines, and even using new gas in case that was the issue. I was trying to figure this one out on my own before giving a shout to the talented guy who brought it back to life for me, because he is several towns over.

 

[bktheking]

Re: '61 40hp Evinrude Lark III won't get full power

Points motors are sensitive to dirt. Any small amounts between the contacts will cause issues. They will run fine like you describe and the next minute stop producing spark, coils will do this too, they heat up and stop working. What is your location?

 

[sperry43]

Re: '61 40hp Evinrude Lark III won't get full power

I just went through the same symptoms I bet you have a piece of carbon grounding out one of your plugs

 

[jdsgrog]

Re: '61 40hp Evinrude Lark III won't get full power

I had the same problem with my 33hp. Check for spark and be sure it is strong blue color and able to jump at least 1/4 inch (or mor). Before I took it out, everything was in order and I got full power 6 times, and then suddenly it bogged down. It idled great but would not go past displacement speeds I found I was running on one cylinder. I'm almost certain that it is an ignition problem. In my opinion, if it's been sitting for five years, replace the coils, points, and condensers. It's a $50-$60 investment.

 

[kenmyfam]

Re: '61 40hp Evinrude Lark III won't get full power

Did the fuel system get a good service before using ?? (carb rebuild)

 

[Chinewalker]

Re: '61 40hp Evinrude Lark III won't get full power

Check the plugs for any evidence of water or moisture. Might be a blown head gasket...

 

[Postmarc]

Re: '61 40hp Evinrude Lark III won't get full power

Thanks again for the great list of suggestions to all. I plan on checking out the fixes this weekend, might be able to squeeze the last run on the lake on Sunday--Wisconsin weather is unusually NOT November-like.

I'm hoping it is just some dirt. Carb was rebuilt, coils looked good, but who knows what little pieces of schmutz were knocked loose the first couple of times this sturdy motor roared back to life. I'll let you know what happens.

 

[samo_ott]

Re: '61 40hp Evinrude Lark III won't get full power

Sounds like running on one cylinder. I'd do a spark test when hot.

 

[Postmarc]

Re: '61 40hp Evinrude Lark III won't get full power

Well, the answer will have to wait until next Saturday. The suggestions about checking spark were correct. I found one of the spark plugs was fouled, the other was fine. I decided to replace the plug, then in a little ADD episode, I then decided to change a slightly cracked hose that ran across the rear of the engine past the plugs, and after doing that, cleaned a little gunk out of the throttle linkage that I noticed, and suddenly realized the day was getting away from me, and I better head out on the lake.

The engine ran the same as before--half speed at WOT.

When I got back home and popped the cover, I found out that the test would have gone a whole lot better if I had remembered to put the @$^*#% spark plug boot back on.

I just sat there and thought, "you idiot". But the weather forecast says one more nice weekend in The Dairy State, so I'll take it out one more time--with both plugs working--and hopefully close out this thread on the weekend. Thanks to all, again.

 

[Postmarc]

Re: '61 40hp Evinrude Lark III won't get full power

Success!!!!!!

After heading out on a very atypical November day in Wisconsin (53 degrees, sunshine), I put in the '57 Edwin Monk-designed runabout with the '62 Lark III and fired it up (to the delight of a pair of German tourists who had rented a Harley and were at the lake taking pictures. ) At the first turn of the key, it purred, and for about three seconds, only on the one cylinder.

Then a blink, I was thrown against the seatback as all 40 horses kicked in. After the initial bow-high surge, she leveled out and was on plane before I knew it. I did a few sweeping turns for the tourists, then headed out on the big lake. It was glorious for the rest of the afternoon.

A big thanks to all who pointed me in the right direction. It is a learning process, and was made easier by the helpful advice I got here. Every hour I spend out with my new old boat I learn more, and I hope to hand out advice someday.

Thanks again, all.

 

[kenmyfam]

Re: '61 40hp Evinrude Lark III won't get full power

Glad you impressed the tourists !!! glad all went well.