1977 140 making popping noise

[cheft]

I have a 1977 evinrude 140 and I have been working on it for some time now and I'm hearing a snapping or popping sound either coming from under the flywheel or in the vicinity of the powerpack or the coils . I can't really hear where it is because the engine is so loud ,but it is intermittent and when I hear the sound stop the engine seems to smooth out and speed up and then it starts again and the engine seems to surge. I was running the engine at about 1400 rpm's and I would unplug the #2 plug, then look for some change, then #3 and when I unplugged # 4 the engine stopped but #2 and #3 seemed like no change at all. Shouldn't there be some change when I unplug a plug? (#2 and #3) anybody got any ideas? the noise?

 

[farmuse]

Re: 1977 140 making popping noise

I had a similar problem with a 1970 115. Turned out it was carbon arcing in the distributor. I cleaned the distributor and rotor with brakeclean and it stopped arcing and run smooth. You might try that it is not hard to get to to clean. Good luck,

 

[Daviet]

Re: 1977 140 making popping noise

You do not have a dist cap and rotor under the flywheel.
You could try running it at night and look for arching. You should run a compression and spark test, it should make a difference when you unplug a spark plug wire.

 

[cheft]

Re: 1977 140 making popping noise

thank you for the advice, I haven't been able to see the arc but I'm almost sure it's under the flywheel. It sounds like it's at the back of the engine under the flywheel. the timer base? If I take off the flywheel I can't start it so i'm stuck. the engine runs good and smooth and then the arc sound and the engine slows and starts to run badly, sputters, tries to die then the sound stops and the engine smooths out again and speeds up. I've checked the wires that I can see for cuts and frayed spots. I unscrewed the powerpack from the engine and put my ear to it and it isn't coming from there either. I'm preety sure it/s under the flywheel. any ideas about what to look for after I pull it off?

 

[wilde1j]

Re: 1977 140 making popping noise

Arcing typically comes from the high voltage side of coils. Again, run at night and it should be easy to see. The other voltages typically are not high enough to make an audible noise.