1958 Lark 35hp knocking

[eclipseturbors]

I purchased a 1958 Lonestar with a 35hp Evinrude Lark. Previous owner had rebuilt the carb, points, coils, impeller, and some other maintenance. The motor starts easy with the choke, but needs alot of throttle with it in gear to start when warm. About half throttle, I can hear a cylinder knocking. When I reduce the throttle a little, the knock goes away. Before I start tearing into this motor, I want to know if this could be just a carb adjustment. Oil mixture is about 32:1 with full synthetic. I plan to return to the recommended 24:1. I'm a big diesel person (4500 hp) and just out of practice with antique 2 stroke.

 

[kfa4303]

Re: 1958 Lark 35hp knocking

Hi eclipse. cool old motor you've got there. You're right that you want to run 24:1 mix in these old 2-strokes. As for the difficulty on start up, the fact that you need to choke the motor makes me think it is running lean. You can try backing out the low speed idle needle about 1/8-1/4 of a turn. If that doesn't do it, you may have an intermittent spark which is causing a mis/non-fire. This is usually due to dirty or misadjusted points. The good news is that the compression is ok, which means all the rest is pretty easy to fix. Here are some great links to help familiarize yourself with you new toy.

Reviving a Vintage Big Twin - Part 1
5.5 HP Evinrude Johnson 1954-1954 Carburetor Tune-Up Procedure (different model, but same steps as your motor)
3 HP Evinrude Lightwin Ignition System Tune-Up 1952-1967 (great ignition tune up link)

 

[HighTrim]

Re: 1958 Lark 35hp knocking

What is the compression of the motor? Start there.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

I'm going to dig out my compression tester tomorrow. I don't suspect poor compression because it started everytime, it just needed quite a bit of throttle. It also died when returned to idle when warm, so I think I'm leaning towards a slow and fast speed adjustements. Can I make these adjustments with a garbage can full of water?

 

[boobie]

Re: 1958 Lark 35hp knocking

Just one thing to remember, a lower unit can also have a knock in it and the sound travels up the drive shaft. Been there.

 

[Daviet]

Re: 1958 Lark 35hp knocking

Remove the plugs and use a screwdriver to check and see if there is any excess play in the wrist pins or rods.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

I will check the wrist pin play when I grab the compression. The knock sounded like it was a cylinder dry firing. It only came at about 1/2 throttle or so. When I pulled back a little, the knock quit. It felt like it still had plenty of power... Actually I was quite pleased with the amount of power out of this little motor. We were still able to cruise at about 20mph with 3 adults. I don't think its a clutch dog sound just by the searching I've done about this motor.

 

[kfa4303]

Re: 1958 Lark 35hp knocking

If the motor tends to drop a cylinder after it warms up, that's usually a sign of a bad ignition component of some sort, probably a bad coil. The stock variety had a 100% failure rate, but the new ones are only about $20 and will last forever.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

I know for a fact that the motor needs an idle adjustment. I plan on making the adjustment and then checking the compression. Hopefully I can then check for spark and maybe find my culprit cylinder. I saw an OHM limit of like .9 for a new one on that article for an older 5hp. I think thats a safe number for a 35hp model or close enough. I hate to believe a new coil would die like that. I'm hoping I can find parts locally here in Tulsa, OK. We have alot of old motors and lakes though.

 

[a70eliminator]

Re: 1958 Lark 35hp knocking

I had an old evinrude that had a rod knock, it let loose and destroyed the motor, I was young and stupid.
Powering up and the knock went away, backing down the knock went away, but in the middle at cruise the knock would be pronounced, I kept doing the power up and backing off thing to show my friend the noise, when suddenly at cruise the knocking rattle changed to crunch crunch crunch pop bang, we had to get a tow.

 

[HighTrim]

Re: 1958 Lark 35hp knocking

The knock is not from an idle adjustment, coil, etc...

Test compression first. Then rotate flywheel so a cylinder is just on its downward stroke. Stick a screwdriver into hole, and push in, to test for excessive play.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

Quick update. I went to throw my compression tester on the motor and found the bottom plug hole that had been heli coiled was trashed. The plug was tight in there, but the threads on both the head side and plug were full of debris. The plug had a larger diameter to it and did not match the one on the top. On the electrode end of both plugs looked fairly normal. I went ahead and pulled the head off. I did not feel any movement on the wrist pin no matter what part of the stroke. The bottom cylinder has some scoring, but I couldn't catch my fingernail in it. I'm guessing from the poor helicoil job. I am now in the hunt for a head gasket locally to put it back together with a spare head that appears to be in good condition.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

Believe it or not, I was able to locate a headgasket locally today for $27. I have a short service manual, but the head bolts say to be torqued to 216 in lbs. Is that correct? Also, the replacement head needs the compression relief covers switched over. Can I just RTV them? I can not get the paper gasket for them.

 

[HighTrim]

Re: 1958 Lark 35hp knocking

yeah 220 to 240 inch/lbs

Start with half torque, then 3/4, then the full 220

Spiral pattern out from middle as shown. You could trace/cut gaskets>?

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

Yeah, I think I have some gasket material at work. I was just hoping to speed things along with black RTV or gasket maker.

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

Which spark plug do I use for this head? What came out of the old head was two different sized J4C Champions. The manual calls for a J4C. I've read about J6C and J8C. Is it just the temp range that changes with the number?

 

[kfa4303]

Re: 1958 Lark 35hp knocking

J6C is probably best for that hp (15hp -35hp), but you can go one higher and use the J8Cs if you do lots of trolling. The J4Cs are best on smaller motors say 10hp and below. Thankfully, they're all pretty common. You should be able to find a pair at any auto store for about $7.

 

[HighTrim]

Re: 1958 Lark 35hp knocking

Don't use J8Cs, much too hot for that model. Stick with the J6Cs.

 

[boobie]

Re: 1958 Lark 35hp knocking

What's the latest on the knock ??

 

[eclipseturbors]

Re: 1958 Lark 35hp knocking

I got the new head on it late last night and then got called to work on a train that was broke down and late. I was able to pull 70psi on each cylinder. It was even almost to the tick mark. I'm hopefully going to be able to grab some plugs today or tomorrow, we are expecting storms and high winds, and see what happens. If I get time, I'll inspect the points and check for spark. I did also find a new pair of coils in with some extra parts! Bonus!