1991 Mercury 150 Thermal air Valve

[pamlicopanther]

I have been working on a 1991 Mercury 150 Black Max with various issues. I recently noticed a broken part on the starboard cylinder head just below the middle plug. A vacuum hose goes from this piece to the carbs. My research shows this to be a thermal air valve. Its purpose seems to be to limit air flow on a cold idle to make it idle better.

I also have found that this little much of nothing piece costs around $200.00.

So how necessary is this piece? I do not mind replacing it, but $200.00 for this little piece is a bit ridiculous.

 

[timguy]

Right, it acts as an enrichener. If it runs adequate while warming up, then don't worry about it. Of course it depends on air and water temp.......so where you live, and how you operate. For me here in Northern MN and NW Ontario, it would be a little more helpful.

 

[pamlicopanther]

I guess I need to block the hose off as it would cause a vacuum leak?

 

[timguy]

This pretty much sizes it up.