1971 Evinrude 100hp runs then dies and dies under load

Joined
Jul 26, 2011
Messages
2
Hello,
I have a 1971 Evinrude 100hp electric shift outboard on a boat that I bought about a year ago. I don't know the history of the motor or the boat. When I first got it, it would run for maybe 30 seconds, then shut off. I first replaced the stock fuel pump with an electric fuel pump. The problem was still there, so I rebuilt both carburetors and discovered they were very clogged, keeping the float valve almost shut. After replacing the carbs the motor started running great (on land with earmuffs). Yesterday, I took the boat out to the lake (with new gas) and it started (reluctantly) and I was able to drive at low and high speeds for 2-5 minutes or so. When I slowed then engine down, it died (it didn't seem to cough or miss or anything, it was almost as though someone just turned it off). I was able to get it to start again after a few minutes but it would die as soon as I shifted into forward. At this point, I drained the carb bowls and the gas coming out seemed especially clear for an oil-gas mix (or maybe I am imagining this).

After being towed back to shore, I took the boat home and hooked it up to the earmuffs again and was able to start the motor (again it was more reluctant to start than I am used to). Once running out of water at just above idle speed, the motor didn't seem to care if it was in gear or neutral, but after running just above idle for a few minutes, the motor slowly lost RPM then died (again it didn't seem to misfire our cough or anything, it just slowly lost RPM until it died). The motor seems to be running cool (I can touch the heads and they are just warm, not hot and I did put in a new water pump and impeller a few months ago so I don't think that it is overheating).

At this point I am not sure what to do. It seems natural to first attack the fuel system by draining the tank and replacing the fuel lines and checking the pump and filter. I will probably also pull the carbs off again and do a quick clean on them as well (though I have probably run the motor less than an hour after the full rebuild). I will also pull and clean the spark plugs (although they are nearly brand new as well). If this doesn't work I will be at a loss. Perhaps the issue is in the ignition system. Maybe the coil or distributor or amplifier is malfunctioning when hot? I don't really know anything about the electrical system on the motor so if this sounds like a reasonable place to look next please let me know and any advice would be appreciated. I should also mention that the amplifier looks almost brand new (based on the condition of the wiring and insulation) and I have tried running with two different, newer, fully charged batteries.

Also, any advice on how to test my repairs without getting halfway across the lake before it breaks down? I think that I should test it under loaded conditions as it seems to run better with no load.

Thank you very much for your help.

PS - I won't be able to do any work on the boat until this weekend, so I may not be able to approach any advice or answer any questions I get until then.
 

guardian452

Cadet
Joined
Mar 15, 2006
Messages
15
Re: 1971 Evinrude 100hp runs then dies and dies under load

I'm no expert, but having a similar engine and having read this forum for some time, I can offer a few words.
As you already know, ensure your fuel system is in good working order. Carefully inspect all hose connections for possible air leaks that would affect fuel flow. Hoses should be flexible so they can maintain an air tight seal. This includes the impulse hose between the original fuel pump and the crankcase.

If you haven't done so already, get a wiring diagram and carefully inspect all wires, connections and grounds. The power packs in these engines are very sensitive to bad battery terminal connections.

Since all four cylinders are running on the same power pack(amplifier) and ignition coil, I would start there. An inductive timing lights would tell you very quickly if the ignition system is shutting down. I'd start with the high tension lead between the coil and the distributor as your problem seems to be affecting all cylinders equally. You'll have to search this forum for the procedure for testing the power pack even though you say it looks fairly new. Caution, the power pack sends a very healthy pulse to the ignition coil, something like 300V, so be careful when testing this part of the system. Make sure the power pack has a good solid ground. Make doubly sure that the wire harness battery terminals are in perfect condition. Many a power pack has been destroyed by a bad connection at the battery.

The power pack could test good when its cold, but fail when its warmed up. My brother-in-law had a similar engine on his boat which would mysteriously stop running when the engine got up to temperature, which was usually a few minutes after he got on plane. Ignition coils can become intermittent as well. But before you go out buying new ignition components, make absolutely sure that all of the fuel system, vacuum hoses, engine wiring, battery terminals and ground connections are in top shape.

Good luck
Sean
 
Joined
Jul 26, 2011
Messages
2
Re: 1971 Evinrude 100hp runs then dies and dies under load

Thanks Guardian!
I will be replacing the fuel line this afternoon and checking the wiring. I have a quick question though... When I put in the electric fuel pump, I removed the original fuel pump and simply closed off the vacuum pulse line from the crank case. Could this be causing me problems? I assumed that the electric fuel pump would supply adequate fuel to the carbs on its own, but maybe not?
Thanks again.
 

guardian452

Cadet
Joined
Mar 15, 2006
Messages
15
Re: 1971 Evinrude 100hp runs then dies and dies under load

I don't think the impulse line is you problem. If it was leaking badly it would only affect the fuel pump and the cylinder its connected to.

Looking at the big picture, you appear to have eliminated the fuel system as the problem as you've rebuilt the carbs, and verified that when the engine died, it wasn't from fuel starvation (fuel still in the float bowls). This doesn't' mean that your fuel system is perfect, but it appears to be getting fuel to both carbs, not just one. I assume the engine didn't die from flooding.

To me, checking for spark as the engine dies is the next, fairly easy thing to do. And since this problem is affecting all cylinders at the same time, I'd start looking at the output of the ignition coil which you should be able to test with a timing light. You should also check at least one of the spark plug leads with a spark gap tester to verify the colour and length of the spark. I believe it should jump about 7/16" and be bright blue. I'd also say to check the spark coming out of the coil lead going to the distributor, but this is not easy as all of the high tension leads are literally screwed into the distributor, including the high tension lead on the ignition coil (which is permanently attached to the coil).

At the other end of the ignition circuit are the breaker points. Since your engine starts and runs, these have to be working to some extent. If they're not, your engine wouldn't run, or it would only run on two cylinders. Its easy to test these as they are wired in series with one end of the circuit grounded to the engine block, and the other end going to the power pack (this is your crankshaft timing signal). You should be able to do a simple continuity test with a multimeter between the metal base of the power pack (ground) and the breaker point wire going to the power pack (Black with White strip?) while slowly rotating the flywheel. I'd disconnect the battery and remove the spark plugs for this test, both for safety and to make it easy for you to turn the crank.

As you turn the crank through one full revolution, you should see four distinct opening and closings of the breaker circuit. If you only see two opening and closings, I'd say that one of the point sets has lost its adjustment and is remaining closed. This would prevent two of the cylinders from firing, but with no load on the engine it may run as others have said on this forum. I hope I got this right?

Beyond on this, you'll have to search the forum for the details on testing the power pack and coil. Like I said, the power pack puts out a pretty high voltage pulse to the coil, and I don't recall the setup you need to measure this to verify the power pack is good.

There's a few other simple electrical tests I'd do;

With the multimeter, watch the voltage going to the power pack when the engine runs and then dies. You'd measure this at the terminal strip on the back of the engine. It will be a Purple wire to the power pack. With your meter Black lead touching the metal base of the power pack, you should be seeing 12-14V on the Purple wire going to the power pack. Make sure to use the metal base of the power pack as your ground and not the engine block. If you're not seeing the full 12-14V, and the voltage is significantly lower than the battery voltage, you've got a voltage drop somewhere which could mean something is shorting or a bad connection. This could also mean a bad ground connection somewhere or something in your charging system is failing. The charging system is a whole other topic. At this point, all I'd want to know is if the power pack is getting full power before, during, and after the the engine dies. If not, there's an electrical problem that must be fixed.

Which brings me to another simple test. Check the ground resistance between the power pack base and the engine block. There should be zero resistance, or next to zero (as in a fraction of an Ohm). If there is some measurable amount of resistance, check the condition of the little braided ground strap between the mounting bracket that the power pack sits on, and the engine block. I'd clean all connections thoroughly until a zero resistance connection is achieved.


I'd Also check the resistance between the engine block and the Negative terminal on the battery. Again, this should be zero , or very close to it. Anything more would say to me that there's a poor connection somewhere due to corrosion or a worn or loose mechanical connection.

DO NOT DISCONNECT ANY BATTERY TERMINAL WHILE THE ENGINE IS RUNNING.
I believe this is a sure fire way to instantly fry the power pack. That's why I'm emphasizing good grounds.

If you don't have a manual, get something. Everyone around here recommends the factory manual. I have a Seloc (please don't flame me) I don't find these Hydroelectic shift engines very intuitive, so you need a manual of some sort with a good wiring diagram to understand how the various electric circuits work and how they're interrelated.

One step at a time.

Good luck.

Sean
 
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