58 Evinrude Lark poor idle and won't get to full speed

[Swendsoa]

Hi everyone,


I have a 1958 Evinrude Lark 35hp that I have been working on for a while now. last year I was able to get it running though not very well. So, this year I have been really trying to get it going well.


the problem: The motor will start and run for about 20 minutes then it will slow and shut off. It won't go full speed, it only seems to want to get up to about half speed. It idles in neutral but you have to hold the throttle all the way forward to the stop point in the neutral position. When you go below that point to shift you have to do it quickly or it will cut out.


What I have done so far:


I set the timing using the special tools, so I'm pretty confident that is good.
I cleaned and rebuilt the magneto.
I have good spark and the plugs look good as well.
I just replaced the gas and oil with non-ethanol gas mixed 1/2 pint oil to 1 gallon gas as suggested in the manual, this seems like a lot to me but doubt this is the problem
I'm over 100Psi on both cylinders for compression
I have checked all the wiring and the fuel lines


This is where I think the problem is most likely:


I cleaned and rebuilt the carb most recently. I was adjusting the level on the float height and in the manual it says, while holding the carb upside down to make the float even with the mating surface of the bowl. I'm wondering if this might have set the float too high and is flooding the engine.


the other thing I have done recently is to adjust the "throttle cam timing" I might be wrong on the name of that but it's the set screw on the linkage that controls the shutter valve as you engage the throttle. The manual was a little vague on how this is done but I think I got it close.


If you know what could be causing my problem or know what I should be checking next please let me know.


Thank you

 

[fdrgator]

I'd say it is runniing on one cylinder. Can we assume you were into the ignition system , so the coils are good, right?

Another thing that will make it run onone cylinder is a ruptured fuel pump diaphragm.

Correct fuel mix is 24:1 (1/3 pint per gallon). But it should run with what you have.

 

[Swendsoa]

yeah the coils are from last year. They should be good. I used my multi meter and tested them when rebuilding the magneto and they were in the range suggested, that was just a resistance test though.

I have a spark tester so I will see if I'm getting spark and make sure it is still nice and strong.

Is there an easy test for the ruptured fuel pump diaphram?

thanks for the help

 

[joereeves]

********************
(Fuel Pump Diaphragm Test)
(Two Hose Type Only)
(J. Reeves)

Note: This pertains only to the regular Two Hose type fuel pumps.

Leave the hoses attached to the fuel pump. Remove only the two screws that attach the fuel pump to the powerhead. Re-insert those two screws and install a nut to each of them so that the fuel pump is securely clamped together. With the fuel line attached to the engine, pump the primer bulb while observing the pressure/vacuum operating hole on the back side of the fuel pump. Should any fuel leak out that hole, the diaphragm is faulty.

If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.

********************
(Fuel Pump Diaphragm Test)
(Three Hose Type Only)
(J. Reeves)

Note: This pertains only to the regular Three Hose type fuel pumps.

Remove only the pressure/vacuum hose that leads from the fuel pump to the crankcase. Leave the other hoses attached. With the fuel line attached to the engine, pump the primer bulb while observing the pump pressure/vacuum fitting that you just removed the hose from. Should any fuel leak out that fitting, the diaphragm is faulty.

NOTE: If the carburetor is obviously flooding, clamp the hose shut that leads to the carburetor.

If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.

********************

 

[timguy]

How did you check your spark? The manual is directing you to mix 16:1, why? 2 stroke as well as many other oils of the old days were of lesser quality than the oils available today. In fact that suggested ratio is often used with regular 4 stroke oil which was more available back in the 50s. With today's oils you can easily run 40 to 1 and in fact in my own personal vintage motors I run 50 or even 64 to 1 on fully synthetic Amsoil 2 stroke oil. But that is just me and I've only been doing it for 40 years without a single failure. This has been a point of contention with many of my peers here and on other forums, but I have the records as well as motors on hand to support my actions. By using higher quality oils of today at extreme ratios like you have demonstrated, more harm than good will result. Another huge consideration is when that amount of smoke is created from vintage outboards other boaters will consider all the pollution and public opinion will direct Legislators to ban the use of vintage 2 strokes. This has already transpired in some states like California. Lakes Tahoe, Mead, and Mohave are also restrictive. Instead what often happens in my case is when I fish locally and the public notices my vintage motors running so sweetly with minimal smoke they actually applaud them.

 

[Swendsoa]

So I checked the spark with my in-line light up spark tester. Both had spark. The light lit nice and bright. I have also in the past held the spark plug about 3/8" away from ground to test them before.

As for the oil, the service manual is a copy from 1958 so it has oil ratio's for that era. In the engine operation section it says 1/2 pint oil to 1 gallon gas, but in the appendix it says 1/3 pint oil to 1 gallon gas. This seems a lot closer to the 24:1 ratio.

I did the 3 line fuel pump test. not a drop came out of the side that goes to the manifold.

I pulled the fly wheel and put the timing tool on the crank and the timing looks to be a little off. It looks like it slipped a little. Is there any trick to keeping it in place?

I'm going to reset the timing this evening. Let me know if you have any other ideas?