Carburettor vent size

[Chazbee]

I have sourced a late hs2 carb with fume extraction port to improve my current rocker cover to air filter arrangement and was surprised to see how big the hole was given that the general opinion of the forum that anything engine side of the carb.should be restricted to about 3mm . The port into the carb is much bigger than 3mm and as it's situated downstream of the mixing point ie. the jet/piston,I'm surprised that it's so big! Should there be some kind of restrictor in the hole or in the hose?

[bmcecosse]

Maybe someone has bored it out - try it on the engine and see ! How big is the hole in the casting when you look in past the throttle plate?

[Chazbee]

The pipe is approx. 8mm O/D and 6mm I/D and appears to be 6mm bore right through into the carb. I know it has'nt been altered at all because it came off my Mini 40 years ago and has been hiding in my garage ever since!

[bmcecosse]

Well - if it ran on the Mini...unless mice have been at it - it will be fine now.... If not, easy enough to fill the pipe with Araldite - then run a drill size of your choice through. Sure it's not one of the 'economy' carbs that were fitted to Metros for a while ??

[Roni]

On mine there is a plastic push in restrictor in the tube on the carb. When ever I take off the hose it always gets trapped in the hose, so they can easily go missing.

[Chazbee]

Definitely off a 1972 Mini which I had from new!
The plastic restrictor sounds like a possibility but why not just make the I/D smaller in the first place?
Maybe I'll just try it and if it runs OK I'll pull a plug to make sure it's not running weak.

[amgrave]

If the stub tube was a smaller the rubber pipe would not be a tight fit

[Chazbee]

I don't think it would have been beyond SU's capability to make an inlet pipe with a large O/D and small bore if that was needed..

[Chazbee]

Update: I I consulted a SU carburettor specialist who said that the 6 mm tube was fine so I fitted the carburettor this week and it works perfectly. I have a further query -after fitting the new carb I noticed that the float chamber wasn't exactly vertical presumably because the angle of the manifold on the mini from which I obtained the carburettor was a different angle to the one on the Morris. It doesn't seem to affect the performance so I am not unduly bothered but looking at the carb that I took off it doesn't appear that you can adjust the angle. Is this correct or am I missing something-would I have to put the float chamber from my original Morris carburettor on to get it sitting vertically or is it the body of the carburettor that's different.?

[panky]

The angle of the float chamber can be altered with different spacer blocks that sit between the carb body and the chamber available from Burlens I think. But check out the one on your old carb first to see if it fits.

[bmcecosse]

Or -you can just modify the spacer block yourself . " SU Carb Specialist " ???? Who/where ??

[GBond]

My carburetor vent was the same and the car ran well for a while but for some reason the engine apparently spit some oil that managed to get all the way to the vacuum chamber and was blocking the piston.

Made a restrictor and it's been working great ever since.