1960's 6HP Evinrude "Fisherman" runs poorly under load

[john7bon]

I inherited an early 60's 6HP Evinrude "Fisherman" model engine. I don't know much about it other than "it ran great 5 years ago."

The engine has a choke, and a Rich/Lean knob that goes from 1 -7 (1 being lean, 7 being rich).

The external fuel tank had about a quarter inch of gas left at the bottom before I added 5 gallons of new fuel.

I changed the lower unit oil, though the existing stuff looked brand new.

It starts very easily (2-4 pulls) and runs very well in neutral. However when under a load (me cruising down the river in the 12' aluminum boat it's attached to) it performs very poorly. With a wide open throttle it moves the boat very slowly, and sounds "bogged down" as if the choke was left on. It sounds/feels like only one cylinder is firing. If I don't leave the throttle wide open, the engine will stall. Adjusting the lean/rich knob seems to have no effect.

That said, my questions are:

1. Knowing zero about the engine's current state or history, what maintenance tasks should I perform from the get-go.

2. Given the symptoms described above, what trouble shooting process should I follow.


TIA,

-JB

 

[scrampbell]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Congrats on your newly inherited motor... I'm a novice but I'd start with the steps below, with the idea that the passages on the high speed jet on your carb needs to be cleared:

1. Check sparks on spark tester -- Probably using a 7/16" gap to test would work. You should change out the spark plugs if you haven't already.
2. Check fuel system, starting from fuel tank and working toward the carbs. You're looking for cracks, leaks, loose fittings, etc. At WOT a loose fitting might start pulling in air which would degrade performance of possibly one cylinder.
3. The likely cause of your issue is clogged up jets on your carb due to sour fuel and/or sediment. So, looks like youre high speed "orifice plug" aka high speed jet is behind the plug at the bottom of your carb float bowl. Take a flashlight and small flathead screwdriver and CAREFULLY remove the piece behind the bolt. You should be able to look down the barrel of that small piece you take out. I don't think it matters too much what you use to clear it as long as you are careful and don't score or scratch the inside. This should get you going.

Good luck and be sure to let us know when and how you get it working right.

 

[F_R]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

90% of no power problems are caused by not running on all cylinders. Disconnect and ground one spark plug wire, and see how it runs. Then do the same thing with the other wire. Chances are, it won't make any difference with one of them and won't run at all with the other one grounded. That is the good one. Now that you have verified that it is running on one cylincer, find out why. Could be a spark plug, could be no or weak spark, could be no compression.

It probably is not the carburetor. Remember it feeds both cylinders, so if it is plugged up, neither one gets any fuel.

Hint: It probably has bad (cracked) coils. They all do unless somebody has already replaced them.

 

[john7bon]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Scrampbell, you're referring to the big guy just below the intake right?

F_R, I was hoping somebody wouldn't say that.

After getting into this thing for the first time, it looks well taken care of. The stater rope looks new, the plugs look brand new (pulled them), fuel lines, and gaskets look new (you can see one of the carb gaskets in the pic).

I'm going to start with Scrampbell's suggestion. Given that it runs good (both cylinders are running okay when in neutral, my theory is that there is enough fuel making it into the cylinders when no load is involved... once the load is applied, the carb can't keep up. Am I crazy?

Anyways, if that doesn't work I guess I'll have to pop the flywheel (I've never done that before; doesn't sound like fun).

Thanks for the advice guys, and stay tuned.

-JB

 

[samo_ott]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

I agree with FR. I would check the coils. it sounds like it's running on one cylinder. BUT, as it has old gas in it for 5 years, it's probably crudded up also, so I would rebuild the carb also...

 

[scrampbell]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

That's the one John. I'm sure you noticed that it's hard to access with the bottom engine cover situated how it is. On my 1984 70hp Johnson, the bottom cylinder is exactly the same way. However, in my case I had the benefit of 2 other cylinders that were easy to access to practice on, so I knew I could clean the bottom one without removing all the parts.

Here's what to do:
1. Get the bolt plug and little washer off however you can (I used box end wrench).
2. I used stripped 18 guage electrical wire to poke into there once the bolt plug was removed, but I'd guess yours is a little smaller nozzle. I'd suggest using a straightened out paper clip to GENTLY poke into there once you have the bolt plug off. Make sure you gently probe around to make sure you're getting as far in as you need to go (make sure you're getting pretty far in). You're likely going to get resistance from 1) the threads on the inside of the bore and 2) the front edge of the piece that you need to clean out (the orifice plug). You need to get your cleaning tool approx 1/2" to 3/4" past the front edge resistance of the orifice plug.

Good luck and let us know how it turns out!

 

[Chinewalker]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Before anything else, do FR's test! It's simple and will likely lead you to the problem. How do you know the motor is running on both cylinders in neutral? These old twins run just "fine" on one cylinder with no load and can fool you into thinking it's something else...

 

[F_R]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Before anything else, do FR's test! It's simple and will likely lead you to the problem. How do you know the motor is running on both cylinders in neutral? These old twins run just "fine" on one cylinder with no load and can fool you into thinking it's something else...

QUOTE: Given that it runs good (both cylinders are running okay when in neutral, my theory is that there is enough fuel making it into the cylinders when no load is involved... once the load is applied, the carb can't keep up. Am I crazy? QUOTE

No offense intended, but yes. If it were lack of fuel, simply turning the high speed knob a bit toward rich would admit more and it would take off. OR, it would die when you give it the throttle.

As Chinewalker said, they will run just fine on one cylinder under no load. Everybody wants to tear into the carburetor first. That only complicates things. Troubleshoot it first, as I described, and you will then know what to proceed further on.

 

[Tim Frank]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

I inherited an early 60's 6HP Evinrude "Fisherman" model engine. I don't know much about it other than "it ran great 5 years ago."
.................

The external fuel tank had about a quarter inch of gas left at the bottom before I added 5 gallons of new fuel.

All of my suggestions have already been offered by someone else...EXCEPT....you have added an entire tank of fresh fuel to a quart of apparantly at least 5 year old who-knows-what.
The first thing you should have done with that tank was to empty it and clean it out.
I would probably still do it and carefully strain (fine mesh) the fuel back into the tank after it is cleaned out.

 

[john7bon]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Update:

1. Used carefully ran paperclip thru carb jet thing, and shot some carb cleaner in there.

2. Checked spark at lead - both resulted in strong spark at over 1/4".
3. Checked spark at plug - both good.
4. Removed flywheel and visually inspected parts underneath (see pic). Everything looks to be in great condition.


5. Performed F_R's suggested test. Problem... Only the top cylinder is firing. Removing the lead to the bottom cylinder resulted in no change in engine behavior. I pulled that plug and shined a light in the cylinder and I can see moister in there (which I'm assuming is gas). According to my father (who drove the boat back to the dock from the launch on it's maiden voyage), it was running strong, then all off the sudden bogged down as I described in my first post. So it's as if that cylinder just quit firing.

So... Now what? I suppose the next step is to check the compression on that cylinder. Any other suggestions?

Thanks to everyone for the advice thus far, by the way. You guys have been great.

-JB

 

[crxess]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Yes, compression check. May have blown head gasket to water jacket. Water snuffing plug.

Looks good under the flywheel!

Have you tested the fuel pump?
Remove from motor leaving hoses attached.
Insert 2 screws with nuts in the not open holes on pump.
Pump up the ball and watch for fuel leaking out the back.
If it has a leak, it will flood the lower cylinder.

 

[john7bon]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Just got back from Sears to pick up a compression tester.

Results:

Top Cylinder: 80 PSI
Bottom Cylinder: 30 PSI

Obviously compression is an issue here.

Where should I go from here? Should I replace the head gasket, check compression again, and then move onto the rings if it hasn't improved?

Any idea what the compression should be in each cylinder?

- JB

 

[crxess]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Go ahead and order the head gasket and get a new thermostat while your at it.
Pull the head, and inspect the gasket. you should be able to see where it failed.

Rotate each piston up and wiggle to check for free play. Should be little to no movement if rings are ok.

If all is good, Place a sheet of 220 wet/dry sand paper on a Flat lever surface and plane the head surface smooth in a figure 8 pattern. May be a little warped so get it level.

Install new gasket and Thermostat. Torque head to 70 inch lbs. Run motor until warm. Let cool and re-torque to 80 in.Lbs.

Take it for a test run.

 

[john7bon]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Bingo!

New gasket and thermostat on the way.

- When installing the new gasket, do I need to apply any kind of silicone or other such sealant in concert with the gasket?

 

[tx1961whaler]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

No sealant on a head gasket

 

[john7bon]

Re: 1960's 6HP Evinrude "Fisherman" runs poorly under load

Replaced head gasket, thromostat, and thermostat gasket.

Compression check showed 75psi on each cylinder.

Started right up. BIG difference from before. Running great now.

Thanks again for the advice guys.

 

[tony.keel]

I inherited an early 60's 6HP Evinrude "Fisherman" model engine. I don't know much about it other than "it ran great 5 years ago."

The engine has a choke, and a Rich/Lean knob that goes from 1 -7 (1 being lean, 7 being rich).

The external fuel tank had about a quarter inch of gas left at the bottom before I added 5 gallons of new fuel.

I changed the lower unit oil, though the existing stuff looked brand new.

It starts very easily (2-4 pulls) and runs very well in neutral. However when under a load (me cruising down the river in the 12' aluminum boat it's attached to) it performs very poorly. With a wide open throttle it moves the boat very slowly, and sounds "bogged down" as if the choke was left on. It sounds/feels like only one cylinder is firing. If I don't leave the throttle wide open, the engine will stall. Adjusting the lean/rich knob seems to have no effect.

That said, my questions are:

1. Knowing zero about the engine's current state or history, what maintenance tasks should I perform from the get-go.

2. Given the symptoms described above, what trouble shooting process should I follow.


TIA,

-JB

This is an old thread I know - but it was very helpful. Thank you. I will pull one spark lead at a time and see what happens. Mine actually cuts in and out, so I think the problem might be an intermittent connection to one spark plug. I replaced the fuel pump and rebuilt the carb already. Wish i read this first.