What’s this hole for? – 1965 40 HP Jounson

[outbdnut2]

Hole in the bottom of the exhaust cover on the powerhead of a 1965 40HP Johnson (see photo) – What’s it for? There is a threaded bushing in it. A Same type of hole and bushing at the top of the cover has a tube going to the automatic choke housing. Nothing shows connected to that hole on exploded views at marineengine, but it’s open to the inside of the housing. If not important, can I just screw in a bolt or other type of plug? Motor runs OK.
Thx, Dave

Hole at bottom of cover in photo:

[Saltymotor]

That’s the air intake for the hot air choke.  Air enters on the bottom and exits on the top into the choke assembly.  There is a small amount of air drawn through the choke assembly into the carb.  At least that’s what it is on my 67 40hp.

 

Steve

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outbdnut2

[outbdnut2]

Saltymotor wrote:

That’s the air intake for the hot air choke.

That makes sense! I’ve seen that done on a lot of 1960s cars with automatic chokes that have a tube running in and out of the exhaust manifold.
Thanks! I have some 1960-1963 40s, and those have a different automatic choke that I believe used hot water. I just did some online searching and found that hot exhaust method of heating the air to the automatic choke bimetal was introduced on these 40s in 1964.
Dave

[Author]

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