37 replies to this topic

[thebullet]

Hi all, when I fit my twin carbs, the current single HS4 has a breather connecton from the carb to the back of the block.

These twin carbs have no breather connections at all so do I just not connect it anywhere? surely can't just leave an open pipe can i?

Cheers.

[Tupers]

You can just stick a small air filter on the end of the engine breather.

[thebullet]

Dont they spray oil everywhere?

[Tupers]

No if you're piston rings are in good shape the breather will just be releasing hot air and a bit of oil vapour from the sump.

[thebullet]

http://www.ebay.co.u...896279983049519

So one like this?

I will have to get one, I guess you just remove the pipe and attach it to the round tube that attaches to the block?

I read they are better than the pipe to the carb body?

Cheers for the replies.

[Tupers]

Yep that'd do the job.

I believe the engine breathers had to be linked back into the carbs originally to stop potentially harmful oil vapour from being released into the air. While this does the job it's not best for performance as you're essentially mixing oil vapour with the inlet of air a fuel into the engine. If you look at the engines on stuff like Miglias and Se7ens they run 3 or more breathers into an oil catch tank with a filter on it to help keep the pressure in the crankcase down.

[thebullet]

Ah so, it is the best thing to do? I wouldn't need a catch tank though I don't suppose.

Many thanks for the replies will get one as soon as I get these carbs on :)

[thebullet]

Read more into this, sounds like it is a bad idea to filter them, what other options do I have? Y piece it to somewhere?

[The Otter]

If it's viable for you, then you could do what some of the old HS2 setups had and add a PCV valve in on to a connection on the manifold. Kind of hard to explain, maybe a quick google will help you understand, but yeah that's what I did on my twins because my carbs didn't have any breather connections either, and I asked a similar question to you a while back, here's a link to the thread, http://www.theminifo...s-on-twin-hs2s/

Here's a picture of what it looks like fitted to the car, you can see the top of the PCV valve is the shiny round thing in between the carbs (ignore the bonnet hinge being used as a tent peg )



Sven.

[Ethel]

That "clacker valve" is one solution, the other way the factory did it was to feed the breather into the air filter casing. The issue is if you connect it to the inlet manifold, you don't want to feed full manifold vacuum to the crankcase when the throttle is shut.

[thebullet]

Hmm really not sure, I can't change my hs2 twins now, might have to just get one of them filters!

[Yoda]

Filters or a catch tank is the more common solution, but the PCV valve is the ideal solution. Ethel, my understanding is that the PCV valve is better to be fed out to the air filter than direct to the manifold, this then eliminates any manifold vacuum to the crankcase, but then OEM PCV valves usually feed the manifold or the carb after the venturi, so i dont really see an issue with the manifold type. and surely the valve is there to prevent this happening anyway?

I may be wrong, so feel free to argue the point.

Personally i would free air the crankcase through a filter or feed it back to the airfilters somehow.

[bmcecosse]

Keep the single HS4, but put it on a GOOD manifold with no hot spot - it's better than the tiny twins........ You MUST suck the fumes away from the breather or you will have oil leaks/nasty smells/oily mess -and the fumes are carcinogenic..... These silly little 'breather filters' are just madness. If you really feel you must use the tiny carbs then get a later one with a breather in the side - or drill a hole and fit a tube !

[Yoda]

You best let all the big agricultural machinery manufacturers know about this because they all run a pcv valve to free air.

[thebullet]

Hmm this is difficult!

I wanted twins to go with my 12g295 head.

I don't want oil all over my engine!



Here is a picture of my twin carbs, I used to have the opening on the manifold but blocked both of them off.

I need to think about this.