Throttling down quickly creates surging?

[sutor623]

Hey guys, getting all the kinks worked out of my ol' girl. Anyone know what this is a symptom of? It ONLY does it when throttling down and then popping it into neutral. If you keep a load on it (in gear) for a few seconds it doesn't seem to do it as much, if at all. Also note that I have all new fuel lines, connections etc (including tank fittings) so I would doubt that it is air in the lines, but ya never know. Check out the vid, you can hear what I am talking about.

 

[Bosunsmate]

I couldnt hear anything untoward, sounds good!

 

[sutor623]

Thanks, but you didn't hear the gurgling/surging? Almost sounded like marbles bouncing around.

 

[fhhuber]

Common 2-stroke engine braking. Water passing the prop faster than the engine is turning the prop so the prop begins driving the engine.

Causes the odd note to the exhaust but that's the only effect you'll get in a boat. You can't over-rev from it on a boat like you could going downhill and engine braking a heavily loaded truck.

Its fine.

Actually you have a good ear to be able to hear it.

 

[sutor623]

Common 2-stroke engine braking. Water passing the prop faster than the engine is turning the prop so the prop begins driving the engine.

Causes the odd note to the exhaust but that's the only effect you'll get in a boat. You can't over-rev from it on a boat like you could going downhill and engine braking a heavily loaded truck.

Its fine.

Actually you have a good ear to be able to hear it.

Ok thanks for the reply. It was just odd to me that she will surge up to 1500rpms for a a few seconds then finally come back down to idle. I don't hardly notice it if I really ease off the throttle, which I tend to do anyways Oh and it tends to only do it if I knock it into neutral.........

 

[jimmbo]

Happens from 12 seconds till almost the end of the video?

 

[sutor623]

Happens from 12 seconds till almost the end of the video?

Yes. Right at the end the engine slows down to a normal idle.

 

[jimmbo]

Today I was at my dealership and they happened to have the 120 hp version of that engine in the test tank. It too was running a little unstable upon returning to idle. With the air silencer off it ran much better, Tipping the silencer about a quarter cup of oil-gas, mostly oil spilled out. When the air silencer was replaced, it was running fine. Something to look at. Your mileage may vary

 

[sutor623]

Cool, gotcha. I have to look at my engine because for some reason the hose that catches the oil in the air silencer and runs it back into the crankcase is gone. Not sure where it is.............