PCV Breather Hose Delete After Weber Carb Install

[Lukehorror]

I had a Weber Carb installed on my '84 720 and it runs great but I noticed while looking at other engines with the Weber carb that the shop capped off my valve cover pcv valve. The internet seems to agree this is bad.

 

This would normally have a hose running to the air filter to bring fresh air into the valve cover. The hose on the Weber carb that should be routed to this is connected to a different part, and I am unsure if I need to move it, or would adding a filter to the valve be good enough?

[datzenmike]

The valve cover fitting should NEVER be closed off. Put the small air filter on the AB valve and route that hose already on the air filter to the valve cover. The reason is that the PCV valve tries to pull fumes out of the engine so filtered air is needed to replace the removed air. However under certain load conditions the flow can be reversed and the fumes should be directed inside the air filter where the carburetor will suck them in and burn them. Those little filters on the valve cover will only let smells into the cab, get oily and drip on the engine.

[Thomas Perkins]

https://youtu.be/u2p8yubP0eU?si=aHv8Bv_Wmnpcfi8w.....Most people that you have installing Webers are clueless on how everything is connected.Get rid of that A.B.Valve, you can sell it.Your top valve on the TVV is to go to the air filter.Leave it open.They also blocked off your line going to your cannister.Here is a video of my set up.

Edited January 12 by Thomas Perkins

[datzenmike]

Yes, the AB can be chucked if you wish. It reduces the high intake vacuum on sudden deceleration at higher speeds reducing the over rich mixture and preventing that annoying pop pop pop exhaust backfiring.

[7twentyguy]

[datzenmike]

Uuuuuh... no. Get rid of the filter and connect valve cover to the base of the air filter housing using a hose.

 

 

5 hours ago, datzenmike said:

The valve cover fitting should NEVER be closed off. Put the small air filter on the AB valve and route that hose already on the air filter to the valve cover. The reason is that the PCV valve tries to pull fumes out of the engine so filtered air is needed to replace the removed air. However under certain load conditions the flow can be reversed and the fumes should be directed inside the air filter where the carburetor will suck them in and burn them. Those little filters on the valve cover will only let smells into the cab, get oily and drip on the engine.

 

Can't really make it any simpler than that and the reason why.

[Stoffregen Motorsports]

I have plumbed the valve cover breather to a nipple on the underside of the air filter housing. It sucks a tiny bit of vacuum and will eat up all the vapor coming out of the valve cover. I have even tee'd the block breather and valve cover breathers together and run them into the air filter housing.

[Lukehorror]

22 hours ago, datzenmike said:

The valve cover fitting should NEVER be closed off. Put the small air filter on the AB valve and route that hose already on the air filter to the valve cover. The reason is that the PCV valve tries to pull fumes out of the engine so filtered air is needed to replace the removed air. However under certain load conditions the flow can be reversed and the fumes should be directed inside the air filter where the carburetor will suck them in and burn them. Those little filters on the valve cover will only let smells into the cab, get oily and drip on the engine.

 

Gotcha, this is what I was thinking but wanted to confirm it. Thanks so much.

[datzenmike]

2 hours ago, Stoffregen Motorsports said:

I have plumbed the valve cover breather to a nipple on the underside of the air filter housing. It sucks a tiny bit of vacuum and will eat up all the vapor coming out of the valve cover. I have even tee'd the block breather and valve cover breathers together and run them into the air filter housing.

 

But then the PCV won't vacuum the vapors out of the crankcase and be replaced with fresh filtered air.

[Stoffregen Motorsports]

36 minutes ago, datzenmike said:

 

But then the PCV won't vacuum the vapors out of the crankcase and be replaced with fresh filtered air.

Not that the way I described pulls much of a vacuum at all, but pulling a vacuum through the crankcase actually makes power. It will pull the piston up the bore.

 

Pulling air from both vents would also help against oil leaks, as it pulls the crank seals tight.

[Foxhound]

On 1/12/2024 at 3:31 PM, Stoffregen Motorsports said:

Not that the way I described pulls much of a vacuum at all, but pulling a vacuum through the crankcase actually makes power. It will pull the piston up the bore.

 

Pulling air from both vents would also help against oil leaks, as it pulls the crank seals tight.

Wouldn't this create more blow-by past the piston rings?  Essentially lowering compression? I honestly don't know. I'm curious because I'm installing a Weber soon and reeeeally don't want to route my breather to the air filter.

[datzenmike]

On 1/12/2024 at 1:31 PM, Stoffregen Motorsports said:

Not that the way I described pulls much of a vacuum at all, but pulling a vacuum through the crankcase actually makes power. It will pull the piston up the bore.

 

Pulling air from both vents would also help against oil leaks, as it pulls the crank seals tight.

 

Yes but pulling from the block vent only and allowing filtered air in to replace it keeps the engine cleaner. Flushes out the humid gas, water and blow-by vapors. The stock PCV system works perfectly. For a race engine there are some advantages to adding a vacuum pump  and keeping the block at a negative pressure. 

[Stoffregen Motorsports]

100%