9 replies to this topic

[radgator1]

Still working on trying to get my car started.  Turns out there weren't any needles in my carbs so ordering some now.  But still confused of proper plumbing of the carbs.  I've looked over the technical section on the SU website but can't seem to find the details I'm missing.  Right we have the linkage and choke hooked up right I think but confused by so many ports/hose nipples on the carbs.  We have the fuel line running into a fuel filter then split and one hose to each carb fuel reservoir float chamber.  What I'm not clear on is why one of the carbs float chambers has 2 ports and the other only one?  Is one a vacuum and what is supposed to connect to it?  Also there are larger hose nipples on the body of each carb.  Again, not clear what is supposed to connect to these.  Thanks for helping a beginner.  A picture with labels would be an incredible help but any input much appreciated.

 

Kevin

[iwatkins]

Hi Kevin,

I'm very familiar with the HS4. What you call nipples could mean something else to me. Do you have a camera phone, digi camera or some other means to post pictures?

If so, lots of pics will help. I'm determined to get you running via proxy.

The larger "nipples" could well be the inlets for the engine breathers from the crankcase. If in doubt, put a small piece of hose on these and seal the other end. This will ensure a good vacuum for starters but please we need pics. Or an airfare to you

Do keep posting.

What needles did you order?

Cheers

Ian

[Vipernoir]

The fuel feed comes up and into the float chamber with two pipes - it then goes from the second of those pipes to the other carb.

 

The two larger 'nipples' on the carb bodies are for the closed circuit breathing.

[radgator1]

Thanks Ian.  I went to the garage where my car is today but forgot my darn phone/camera.  I'll get a pic up as soon as I can early next week.  So you can run the crankcase breathers to the carbs or just put filters on them (which is what I was planning on doing) and cap the inlets on the carbs? 

 

Until I can get the pics up can you confirm that it is correct to split the fuel line before it goes to the carbs?  The way one carb has 2 places to connect hose and the other only one made me think maybe you are suppose to run the gas only to that one then run a hose from the second connector to the other carb with only one fuel line nipple?

 

Thanks again for the help.

[radgator1]

The fuel feed comes up and into the float chamber with two pipes - it then goes from the second of those pipes to the other carb.

 

The two larger 'nipples' on the carb bodies are for the closed circuit breathing.

Great man, thanks.  I just posted as much.  Is there a problem with capping that second post and splitting the fuel line like I have it?

[Vipernoir]

I don't see why you can't run it the way you have, but it's a tidier install if you do it 'properly'.

[jaydee]

So you can run the crankcase breathers to the carbs or just put filters on them (which is what I was planning on doing) and cap the inlets on the carbs? 

 

 

There are pros and cons.

Connecting them to the carb is a much better option, oil vapours are extremely toxic and messy.

In some cases twin SUs are a pig to get balanced correctly with the breathers connected though.

Mines have the beathers connected to the air filter.

[Klevdo2202]

[radgator1]

Thanks for the replies and the pic.  Very helpful.

[Stevie W]

Hi,

 

This is a pikky of my twin 1 1/4 SU carbs.

 

I elected to use the Cooper "S" set-up with the "gulp" valve in the centre between the 2 carbs. On the hose connector on the right, I attached a short piece of hose with a plastic "Y" piece then connected each of the 2 breathers (flywheel housing and timing chain cover) to the "Y" piece branches.

This gives you a slight vacuum in the crankcase and helps draw out any blow-by gases. The "gulp" valve prevents any flames from entering the crankcase should there be a backfire through the inlet manifold!!! 

 

Hope this helps!!

 

Steve.