RPM's drop at hi speed for 3-5 seconds

[gbeardmore]

Posted this on the Antique Forum as well. (Sorry if that's considered double-dipping)

I've got a '61 Evinrude 40hp Lark that has run great 'till last night. After it was warmed up, at hi speed, every 30 seconds or so the RPM's would kinda drop for maybe 3-5 seconds, and then come back. Sounded like the engine was "lugging". No weeds on the prop. Maybe a fuel issue? I don't know, as I'm really a neophyte. Any thoughts? Thanks!

 

[Daviet]

Re: RPM's drop at hi speed for 3-5 seconds

Maybe loosing spark to one cylinder?
Hard to check if it only happens for so short a period of time.
When was the last time the flywheel was removed and ign componets checked, how do the plugs look?

 

[gbeardmore]

Re: RPM's drop at hi speed for 3-5 seconds

Maybe loosing spark to one cylinder?
Hard to check if it only happens for so short a period of time.
When was the last time the flywheel was removed and ign componets checked, how do the plugs look?

The plugs look fine. Gapped properly, with just a little bit of "wet" oil on them. Pretty normal looking from my limited experience.

I couldn't say about the flywheel, points, etc. I got it last August and don't know what the PO did. All I know is it ran fine 'till last night. I suppose I SHOULD take a look under it.

Thanks!