Landyfella
Active Member
Thx very much
Chris
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Thx very much
Chris
TheMegaMan
Well-Known Member
Connecting the pipe to the breather on the rocker cover makes sense if the port on the carb is *before* the throttle butterfly. The purpose of this would be to feed any surplus pressure/fumes from the rocker cover back into the inlet air stream to burn it rather than having to clean it up in any way (or just vent to atmosphere, and potentially be more polluting).
However, from the photo of the carb, it looks like the port/pipe is *after* the butterfly, ie. next to the inlet manifold. In this case, when the engine is running, it'll be pulling a vacuum when the butterfly is shut, and if this is connected to the rocker cover breather, you'll be sucking a lot of air through into the manifold (bypassing the carb) that's likely to really screw with your idle mixture.
So I'd say that @Bobsticle is probably correct, and it's a vacuum hose intended for a brake servo. If you don't have a brake servo, blocking off the pipe would be an appropriate thing to do. I've used bolts for exactly such a purpose.
Adam
However, from the photo of the carb, it looks like the port/pipe is *after* the butterfly, ie. next to the inlet manifold. In this case, when the engine is running, it'll be pulling a vacuum when the butterfly is shut, and if this is connected to the rocker cover breather, you'll be sucking a lot of air through into the manifold (bypassing the carb) that's likely to really screw with your idle mixture.
So I'd say that @Bobsticle is probably correct, and it's a vacuum hose intended for a brake servo. If you don't have a brake servo, blocking off the pipe would be an appropriate thing to do. I've used bolts for exactly such a purpose.
Adam
Landyfella
Active Member
Thx, much appreciated. funnily enough I was thinking about adding a servo. is it difficult? What buy one from a later car? If so which one and will I need to modify the wiing?
Thx.
Thx.
TS2304
Active Member
I am no expert, and happy to be wrong, but on my S3 2.25 the brake servo hose goes direct to the manifold and the carb bottom pipe connects to the breather system. Certainly that's how it was when I got it over 10 years ago and pretty sure the set up is standard - looks that way from the manual at least (pic below). On mine you can see the brake servo pipe heading off bottom left to the servo unit. Breather pipes to outlet on the metal breather case and bottom of carb (which is a zenith).
But as I say - no expert; could be wrong but it's worked well for me with sweet idle and gases all in required range.
But as I say - no expert; could be wrong but it's worked well for me with sweet idle and gases all in required range.
TheMegaMan
Well-Known Member
Well, it seems I'm no expert, either!
I've just been out and looked at mine, and you're quite correct that the brake servo pipe connects to the manifold directly.
But the rocker cover breather on mine only goes to the elbow on the air inlet to the carb. I do have the carb adapter that the diagram shows, but the hole on that is simply blocked off with a bolt. I guess the port on the bottom of @Landyfella's carb is equivalent (I don't have a port like that on the body of my Weber carb).
I'm guessing this was a modification to more recent engines (post '77) to somehow help with emissions, but I really don't understand how this works. It looks to me just like it's bypassing the throttle, albeit with a small bore pipe that might restrict the airflow enough that it's tolerable. You don't usually want any air leaking into the manifold after the carb, and connecting this up to the breather seems to be doing exactly that.
Ah well. But I would still say the easy thing to do and keep it simple is just to block it off. My '82 Landy also passed it's MoT emissions test without the breather-carb pipe fitted. Maybe a PO has simplified my installation.
Adam
I've just been out and looked at mine, and you're quite correct that the brake servo pipe connects to the manifold directly.
But the rocker cover breather on mine only goes to the elbow on the air inlet to the carb. I do have the carb adapter that the diagram shows, but the hole on that is simply blocked off with a bolt. I guess the port on the bottom of @Landyfella's carb is equivalent (I don't have a port like that on the body of my Weber carb).
I'm guessing this was a modification to more recent engines (post '77) to somehow help with emissions, but I really don't understand how this works. It looks to me just like it's bypassing the throttle, albeit with a small bore pipe that might restrict the airflow enough that it's tolerable. You don't usually want any air leaking into the manifold after the carb, and connecting this up to the breather seems to be doing exactly that.
Ah well. But I would still say the easy thing to do and keep it simple is just to block it off. My '82 Landy also passed it's MoT emissions test without the breather-carb pipe fitted. Maybe a PO has simplified my installation.
Adam
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TS2304
Active Member
To be fair mine is like that because that’s what it was like when I got it and I went with the ‘if it ain’t broke’ approach! Not always the best way to go with series considering what POs may have done I grant you but in this bit at least I’ll keep it til it breaks then put more thought in to it!
