What is this on the carb?

[rocket350]

I asked a week or two ago with a good description, but no one seemed to know what I was talking about. I came across the picture, but still doesn't say what it is. It pushes down on the power valve.

So my question: What does it do, and what does the power valve do? Mercruiser 3.0 carb

 

[WizeOne]

Re: What is this on the carb?

I have no clue as to what the doohickey is in your illustration. However,the power valve operates off of the absense of vacumm. Under high loads (low vacumm) the valve opens and richens the mixture. This both increases the power and keeps the motor from leaning out and detonation.

In short, main metering jets cannot be sized to adequately accomodate the full range of fast idle to full throttle. If you were to jet for full load, the motor would load up at lower throttle settings.

Not all carbs use power valves. Some like the Edelbrock 1409 use metering rods in addition to the main jets. Like power valves you can alter the amount of fuel they dump by changing their sizes. However, most stock power valves sizes are suitable for their intended applications.

 

[Don S]

Re: What is this on the carb?

The item you have pictured is the valve the opens and closes the power valve.
When the engine is running at idle, the pictured valve/spring assembly is pulled up by vacuum. Thus closing the powervalve below it.
When you give full throttle, the vacuum goes to zero and the spring pushes down on the power valve opening it and allowing more fuel to the engine.

 

[rocket350]

Re: What is this on the carb?

Thanks, now I understand.

Would it be obvious if the Power Jet system an issue? It runs awesome, but WOT is lacking 2 -400 rpms. Just wondering if this could be an issue...

 

[Don S]

Re: What is this on the carb?

That is probably not the problem.
Head up to the adults only stick, and read the thread on WOT problems. #12