rpm increase and decrease w/o adjusting throttle

[Sailwood]

Yesterday I noticed the engine rpm increase for several seconds, then return to its previous rpm without touching the throttle. It seemed to irregularly cycle. We're talking several seconds, then normal, then several seconds. There is no discernable change in hull speed when it revs higher (perhaps 200-300 rpm). Clutch/reversing gear problem? This occured on the way back in after a 3 hour sail. No similar problem previously. Engine otherwise is running well at present.

Doug Soden
ASPEN Columbia 29 #131

[zanchi]

I have the same issue!

[Dave Neptune]

S & z, it could easily be the alternator kicking in and out. Check the charging levels during the next episode. You can also disable the alt via the belt or unplugging the "exciting" wire to see if the surging goes away. The engine will run a long time on the battery alone.

Dave Neptune

[ndutton]

Concur, intermittent alternator load.

[tenders]

I vote for intermittent valve sticking. Add an ounce of Marvel Mystery Oil for every five gallons of gas in the fuel tank, more or less, and see what happens after an hour's running.

(Note, original post is from 13 years ago.)