What's Up With The Air Vents? Why?

I’ve been getting a lot of questions about the breather vents from several customers and I haven’t properly addressed them.
Below this message, I have forwarded one of my responses to a curious customer. Which I believe was my best reply as I try to explain the purpose.
Hi Billy, 
I apologize for the late reply, it's been crazy at the office. I've had several folks ask me the same question and I'll just post a snip-it of a recent email I just sent to the customer about the breather vents....
"......Hey Eddie
I figured if I wanted to build a proper propane kit I should take the generator and the kit to an engine test facility and have it bench tested. 
I also hired an engine technician to work with me, who's been in the field for over 20+ years and had him advise me on alternative fuels. 
He looked at the equipment I had hooked up, and noted that the demand regulator is set to atmospheric pressure on one side of the diaphragm and the other side relies on negative pressure from the engine. There is a drawback to this because the demand regulator is not sitting inside the generator. The generator is a closed frame genset and the demand regulator is not going to know the difference between vacuum from the intake box and additional vacuum created by the engine cooling fan blowing across the air cooled engine. 
So the inside of the generator is not at atmospheric pressure..... This is a problem, you can see evidence of high vacuum by running the generator as is on gasoline and opening the maintenance door cover. You can really feel the door being sucked back shut. 
So we started prodding around with a vacuum meter and started drilling holes on the genset housing and found pockets of high vacuum in the area's where the vents are currently placed. We got it close enough to satisfy the demand regulator without causing it to dump fuel into the engine during high idle. Low idle on eco mode on was fine, it was the high idle that was an issue. So we added the additional fuel adjustment that sits on top of the demand regulator to limit excessive fuel flow during high idle.
Even though there is a fixed jet orifice size in the fuel adapter, the additional fuel adjustment allows for fine tuning……" 

I'm sure our direct competitor runs fine running without the breather vents, but it doesn't mean it's the right way of doing it. But what about the early model EU2000i they say is NOT compatible with their kit?

Our kits work on all EU2000i or EU2200i regardless what serial number it falls under. Which in that aspect tells you a lot about our product..... meaning we walked the extra mile trying to problem solve what they couldn't.

Hope this answers your question. Have a good night. 

To better understand why the breather vents is needed, you also need to know how the demand regulator works.

The demand valve/regulator (aka zero governor) allows fuel flow when the carburetor vacuum (aka suction pressure) acts upon the diaphragm to open the internal valve and allow passage of fuel. The diaphragm is moved with each intake stroke of the engine. The amount of fuel that enters the carb varies with the amount of vacuum, the length of the hose between the carb and demand valve, and the inlet pressure (along with proper pipe sizing to keep up with the flow) at the demand valve. Also, the fuel is trimmed using the load block (or a needle valve) to match the needs of the engine. Once the fuel rate is properly set at full load, then the air fuel mixture will naturally track down along with engine demand as the load decreases. The carb vacuum is proportional to air flow thru it, so it decreases as the throttle is closed more and more. The A/F ratio needs to be set correctly as running too rich can cause exhaust valve failure.

Due to the way the valve works (using vacuum to allow fuel flow), the demand valve also acts as a safety device to shut off the fuel when the engine is shut down.

Demand valves can also be sensitive to being laid on their side. Gravity tends to mess with the diaphragm's response to applied vacuum. The demand valve works best if the diaphragm is vertical.

The demand valve works differently than a pressure regulator. A pressure regulator (which is used to feed propane to the demand valve) tries to maintain a constant pressure at the outlet regardless of input pressure changes or fuel flow.*See video below.

Our fuel adapter helps with maintaining consistent vacuum signal especially during low engine idle "Eco Mode ON". Without it, the demand regulator will think the engine is shutting down and will eventually cut fuel flow.

When this happens, the generator will attempt to kick up the RPM to stay running and then try to idle back to normal. This is what cases "idle surging" because the demand regulator is fighting with the generator due to poor vacuum signal.

*See how our fuel adapter works in link here ---> https://grenergy-us.com/pages/facts-about-grenergy-designed-fuel-plate-adapter

In summary, the added breather vents and our patented fuel adapter is what makes our kit work extremely well.