'74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

[harrylarson]

Last year my '74 115 hp Evinrude ran great 99.5% of the time, however it would occasionally run as if it were cold or wasn't getting fuel, it was getting more frequent then my last outing on the water it ran super for about 20 minutes then started to stammer as if it was not getting fuel. I barely made it back to the dock and when I checked the motor it was cold. First thing this year I replaced the thermostat, it was stuck, started it up in tub in garage and it idled fine for 15 minutes, engine was warm, problem solved I thought, then it started to stammer along again. I throttled up, still barely ran, I squeezed the ball repeatedly, still stammered. I don't understand how it can run so well for a while and then so poorly, if it's the fuel or pump why doesn't it do it all the time? Any ideas?

 

[emdsapmgr]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Check the engine for spark on all 4 cyls. after it warms up. Weak/old ignition components tend to fail when they heat up to normal operating temperatures. Might take about 15 minutes....

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Thanks for responding. Can you help further? I assume when you say check for spark you mean, warm motor, stop, pull one plug or all plugs turn ignition and check each. Correct? Also, I understand there are some "Top Secret" files here that explain checks like this but I can't seem to find them. Can you explain? Thanks.

 

[emdsapmgr]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

You are on the right track. You can also use an inductive timing light to check spark. The flashes in the gun will show if it's misfiring, no spark or weak spark. The top secret files are at the top of the first page of this forum.

 

[DJ]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Here are the tips.

http://forums.iboats.com/forumdisplay.php?f=31

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Got the files. Thank you!

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Started her up tonight, with induction light on wire for #1 cylinder steadily strobing light, same on cylinder #3. When the light is attached to wire for #2 or #4 cylinder it does not strobe steadily but sputters in sequence with sound of the motor. Am I missing on these two cylinders? What do you think? Any help would be greatly appreciated. Thanks.

 

[emdsapmgr]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

If you can see the differences in the flashes, then you probably have an ignition problem. It's always possible the coils are the problem, but they generally have a very low failure rate. That leaves the power pack, the stator and the timer base. All expensive. Some time spent troubleshooting will avert purchasing the wrong component. CDI electronics has some good troubleshooting tips on their website for these older electronic systems. Starting at page 35 you will find specific information about your model.

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Thank you. I found the info from CDI and some in my Seloc manual I'll start to look into it. Thanks again.

 

[emdsapmgr]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Some of the voltage tests mentioned in the troubleshooting sections require a special "peak reading" voltmeter. Different from the normal household meters. (such as the voltage output of the stator, around 150 to 160 volts..... or .3 volts from the timer base.)

 

[Bamaman1]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Did you notice if it was throwing out a stream of water at idle? Sometimes the water pumps will go out, and the engines can partially sieze as they warm up. After they cool down, they'll run good--until they heat up.

I suggest you drop the lower unit and check out the water impeller. It's a cheap and easy job to complete.

I speak from experience, as I have only changed my impeller once in 25 years. Water pumps and lower unit oil are the most overlooked things in the boating world.

 

[Sixmark]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Did you notice if it was throwing out a stream of water at idle? Sometimes the water pumps will go out, and the engines can partially sieze as they warm up. After they cool down, they'll run good--until they heat up.

I suggest you drop the lower unit and check out the water impeller. It's a cheap and easy job to complete.

I speak from experience, as I have only changed my impeller once in 25 years. Water pumps and lower unit oil are the most overlooked things in the boating world.

In other words you have been lucky

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Thanks for the replies, first when this boat became mine four years ago it had sat for I don't know how long; thanks to the Forum's advice I replaced the water pump before I ever tried to start it. Plus I just replaced the thermostat, when it idles you can keep your fingers on any head for as long as you like, gets warm but not hot. Second I realize after looking at the inductive light that it's really not running that well anytime even when I thought it was idling fine I can see the differences in the flashes. After reading the Seloc Manual and checking with some Forum Threads the Neon Light Test it mentions is fairly rare and outdated. Reading the CDI Troubleshoot I wondered if my $5.00 Harbor Freight voltmeter would work, Emdsapmgr confirms it won't. However, the CDI page 36 suggests swapping the timer base wire sets from cyl. 1 & 3 with 2 & 4 to see if problem follows. I might try this but CDI doesn't say what this would mean, bad timer base, stator, power pack?

 

[harrylarson]

Re: '74 115 hp Evinrude Idled fine for almost 15 minutes then barely runs

Could someone please confirm what I understand is a test of power pack. I will switch orange coil wires for cylinders 1 and 3 at pack with wires for 2 and 4 respectively, start motor and check with inductive light to see if intermittent or weak spark moves to the other side. If it does the pack is bad, yes? Thanks. (It is OK to start motor with wires swapped, or should I only crank with starter?)