Air Constriction?

[Rather.B.Fishin]

Hey guys,

I have a restored 1960 40hp Johnson. Last time I took the boat out I noticed that at idle, in neutral, the engine wanted to die but I would open the front(where you can access the pull rope) and the engine would liven right back up. What is causing this? And should I even worry about it since I dont sit around in neutral much? Thanks

Rather

 

[Chinewalker]

Re: Air Constriction?

Most likely a small exhaust leak. With the cowling open, motor gets fresh air. Leak becomes less pronounced at speed as the exhaust outlet down below in the lower unit actually helps scavenge exhaust out of the motor due to low pressure/vacuum - essentially sucking the exhaust out, enough to reduce the amount ending up in the cowling. At idle, the exhaust is under pressure in the housing, some of which exits via the exhaust relief in the back of the cowling. With a leak somewhere, it is apparently also exiting into the cowling area.

 

[Rather.B.Fishin]

Re: Air Constriction?

Thanks chinewalker. What can I do to fix this? How can I find the leak?

 

[Chinewalker]

Re: Air Constriction?

Might be able to find it visually. Sometimes evident due to oily sludge eminating from a gasket area - either along exhaust cover edge, or at base of powerhead. Could also be the rubber booty that connects the inner exhaust relief to the outer housing in the rear. A spray bottle of soapy water may help find it, too, as a leaking area will bubble up.