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1974 25hp outboard boggin issue

K

kos

New member
Hey there, I am new to the forum and looking to see if I can get a hand diagnosing my engine.

I am familiar with 2 stroke engines but have never worked on a marine 2 stroke and not sure how similar they are. I have a 1974 25hp evinrude that when I bought it, it was running fine. Go to take it out on the lake and have some bad bogging and sputtering issues. The only thing I have done is replace one of the coils as it was cracked and when I pulled the plug on that one it looked wet. But after replacing it, it was still doing the same thing. However the wet plug didnt seem to be an issue anymore. Dont understand that part.

I checked the spark on both plugs and swapped both coils to the plugs just to make sure and spark seems good. I dont have a compression tester so I simply plugged the holes with my thumbs just to get some idea if there was something really off. The "thumb" test felt the same on both cylinders. I know that doesnt mean much of anything other than at least there is comparable compression on both, doesnt mean it is high, just that I wasnt getting some real soft on one and not the other.

I made a short video of it running. There is another weird noise in the background which is a water pump I was using to drain some of my pool. You will really notice it at the end of the video and in hindsight I should have turned it off. But disregard.
1974 evinrude motor running video

Before I randomly go about tearing it apart, I figured i would post to see if there is a direction I should start. I was thinking there was some sort of fuel issue since I got one of those new EPA gas tanks. I did pump it with the bulb point upwards and really my next step was to just give the carb a good cleaning. Any help is greatly appreciated!

Thanks
 
Do purchase a compression gauge... they're cheap and available just about everywhere.

Also purchase a spark tester (automotive parts store) that you can set to a 1/4" gap. The gap is important. Your magneto model engine requires the gap setting of 1/4" for the spark to jump... the later solid state ignition models require a 7/16" gap. NOTE... Testing the spark using the spark plugs or any other gap setting is a waste of time.

The spark must jump the required gap with a strong blue lightning like flame... a real SNAP! Does it?

Now, if you have compression and the proper spark... that leave fuel.

You state that the engine has bogging and sputtering issues... BUT... you don't say when! However, if this bogging is when you apply throttle, that normally indicates that the carburetor is fouled, clogged, gummed. In which case, remove, clean, and rebuild it as needed.

Make sure that the brass high speed jet that is located horizontally in the bottom center portion of the float chamber is absolutely clean.
 
joereeves said:
Do purchase a compression gauge... they're cheap and available just about everywhere.

Also purchase a spark tester (automotive parts store) that you can set to a 1/4" gap. The gap is important. Your magneto model engine requires the gap setting of 1/4" for the spark to jump... the later solid state ignition models require a 7/16" gap. NOTE... Testing the spark using the spark plugs or any other gap setting is a waste of time.

The spark must jump the required gap with a strong blue lightning like flame... a real SNAP! Does it?

Now, if you have compression and the proper spark... that leave fuel.

You state that the engine has bogging and sputtering issues... BUT... you don't say when! However, if this bogging is when you apply throttle, that normally indicates that the carburetor is fouled, clogged, gummed. In which case, remove, clean, and rebuild it as needed.

Make sure that the brass high speed jet that is located horizontally in the bottom center portion of the float chamber is absolutely clean.
Click to expand...

Well it was hard to tell if the spark was that bright, I was outside when I did it in the sun, but didnt use an actual spark tester. I realize the compression needs to be tested properly, but before going to buy more things I was curious if there was a clear path. The motor in the video was doing the same thing at idle as well as under load, most of that video is just idle though.
 
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