13 replies to this topic

[babsbrown]

Evening guys

I'm running a weber carb which didn't come fitted with a crankcase breather port.
I tapped one into the inlet manifold which created a huge air influx and weakened my idle far too much.

I've bought a new airfilter which has a port attached, to allow fitment of the breather hose.

Should this provide sufficient to draw the crank case fumes out and relieve the pressure within the crankcase?

I don't want to start bursting seals. The airfilter does also exposed to the outside of the engine bay as it was so tall I had to make a vent in the bonnet.

Thanks, Luke

[Ethel]

That has been used on production cars. An alternative would be to add  a PCV valve, as used with twin SUs.

 

Several modern cars use similar, but much cheaper, plastic versions

[babsbrown]

That has been used on production cars. An alternative would be to add a PCV valve, as used with twin SUs.

Several modern cars use similar, but much cheaper, plastic versions

Excellent, Thanks Ethel

[68+86auto]

As has already been suggested, I would fit a PCV valve between the breather and manifold along with a vented oil cap.

 

There are various options commonly available which have two barbs. The original type is expensive.

Edited by 68+86auto, 13 May 2026 - 11:43 PM.

[timmy850]

If you can, it’s best on a Weber manifold to tap into both runners and T them together before the PCV. If you only use one runner it can effect the mixture on those 2 cylinders

[babsbrown]

Thank you gents, I'm really new to Webers so appreciate the help.

[babsbrown]

If you can, it’s best on a Weber manifold to tap into both runners and T them together before the PCV. If you only use one runner it can effect the mixture on those 2 cylinders

Ahh I never even thought of that. Currently one size is plumbed into the brake servo. I'll have to think of a way to negate that. Unless I can adjust the PCV enough to equal the vaccum demanded by the servo.

Edited by babsbrown, 14 May 2026 - 06:16 AM.

[Spider]

As another option for a PCV Valve, there's many used on the small Jap and other imported cars that are an In-line type that might suit your installation a bit neater, eg:-

https://www.repco.co...yOOnA8C3qWgw4pK

 

(sorry that's an aussie store, but you'll get the idea)

Be sure you're running a vented oil filler cap too.

[whistler]

As another option for a PCV Valve, there's many used on the small Jap and other imported cars that are an In-line type that might suit your installation a bit neater, eg:-

https://www.repco.co...yOOnA8C3qWgw4pK

 

(sorry that's an aussie store, but you'll get the idea)

Be sure you're running a vented oil filler cap too.

That link is blocked on both of my browsers. 

[Ethel]

Reckon it's a regional thing to prevent it getting flooded by spammers.

 

Spider might have meant something like this

 

Audi, Renault & VW use diaphragm versions, closer to the twin SU set up, they all must do a similar job of  shutting out excess manifold vacuum, though some may be at least as much about shutting under turbo boost pressure. If you can suck one shut without busting a lung it's likely up to the job.

[Spider]

 

As another option for a PCV Valve, there's many used on the small Jap and other imported cars that are an In-line type that might suit your installation a bit neater, eg:-

https://www.repco.co...yOOnA8C3qWgw4pK

 

(sorry that's an aussie store, but you'll get the idea)

Be sure you're running a vented oil filler cap too.

That link is blocked on both of my browsers. 

 

 

That's handy !

 Fuelmiser PCV-013.jpg   23.11K   1 downloads

These are for a Toyota Corolla (and possibly some other cars. One side is 10mm, the other 13, I don't know if you guys have Fuelmiser brand parts, but this is a PCV-013

[babsbrown]

Ahh excellent thanks for that. Yes I think fuelmiser predominantly just supplies the Australian Market. But no doubt I can pick an equivalent up locally.

I tested the car today with the crank case breather pipe going into the airfiler. It idles great around 14.6 AFR.

The idle jet will definitely want changing depending on how much, if any the PCV valve will effect air influx, once I install one.

I was hovering about 11.8-12.4 AFR at light cruise so abprutly turned back to avoid borewashing the thing.

[Ethel]

If you feel the need you could always tee into your breather hose for a manometer of some description. You only need 2-3 psi of vacuum

[babsbrown]

Thanks Ethel, and everyone else for their help and suggestions