Need new plug

[garbageguy]

What plug size/type should I get to replace the leaker on the aft starboard exhaust manifold on the GM 350 in this carb'd IO boat? When this boat was repowered about 8 yrs ago, I think this manifold plug mighta been just something around put on the get things running. I shoulda measured it last time I was at the boat. Unfortunately pics wont insert or copy in. All input appreciated.

 

[Scott Danforth]

Either 1/2" NPT or 3/4"NPT

 

[dubs283]

National Pipe is not measured in inches

Based on OP stating a carbureted engine WAG would be 1/4 NPT, preferably in brass

 

[Scott Danforth]

VP manifolds have 1/2" NPT on the bottom and 3/4" on the ends

 

[garbageguy]

Thank you.
Wish I could get the pic uploaded - there's a very short piece of closed-end hose on there attached to the end of manifold with a band-clamp. And that rubber stop is now slowly leaking - seems like it was just a barn-job, and a threaded metal-plug should have been put in there. Does this seem correct?

 

[dubs283]

There were a few years in the early/mid 90's during the OMC crossover years that volvo did use the rubber cap plug with a hose clamp over the cast barb on the end of the manifold

Remove the clamp and rubber cap and you'll see the cast barb end. Local hardware store will hopefully have a suitable rubber cap for replacement

 

[garbageguy]

I'm guessing that's OK/best to do with boat in slip, engine cold/not running. Correct?

 

[dypcdiver]

Depends on the water level outside the boat.

 

[garbageguy]

water level outside the boat is where it should be and that water level is lower than the subject location of the plug on the exhaust manifold - pic will still not post