HS6 Carburetor

[Steve Huneck]

Well, once again I am looking for a little advice. I just purchased a new set of HS6 carburetors for my BJ7 from SU in England. They are not exactly the same as my originals. There is an additional tube coming out on the manifold side of both carbs. On the rear carb it is next to the vacuum advance connection. My guess is that they are for some kind of synchronization, but I cannot find a reference to this anywhere. The only other thing is that the parts manual has the carburetors as part number AUC 981 and the box they came in has AUC 981T marked on it. I am sending an email to SU, but while I wait for them to respond, I thought I would try the forum. Any thoughts or comments are appreciated.
Thanks,
Steve

 

[Johnny]

Don't know why there would be any additional tubes. Here's a photo of my HS6 carbs prior to rebuilding. I believe the carbs are as original.

 

[Steve Huneck]

That is how my originals look as well. Here is a picture of the new ones:

 

[Michael Oritt]

Those are balance tubes and you simply put a piece of hose between the two.

I use these same carbs on my Elva Courier (MGA 1600 cc. engine) and have a brand new unused, shiny polished spare set for sale, complete with intake manifold though for an MGA head.

If anyone is interested please contact me privately.

 

[Randy Forbes]

Nope. Check out the Moss Motors catalog for late 60s-early 70s MGBs, and you'll see that they're tied together with hoses and a *Y* adapter, connected to either a PCV or the top of the rocker box.

In fact, using that criteria, you can order all the parts to need to complete the circuit.

Frankly, that will be much neater and cleaner than running the hose into your aft air filter.

 

[Michael Oritt]

Randy--

Was that addressed to me?

If so, I do not run them into either air filter, merely have a piece of 1/4" clear plastic hose going from one to the other. See in the attached photo that I have my carbs oriented so that the tubes are facing outward and give the hose a better lead away and up from the heat of the engine and exhaust manifold which sits just under the intake shown.

The intake manifold shown is a tubular Maniflow which I switched to early this year to replace the Aluminum factory one. It solved several problems for me--it made the removal of carbs mounted on the intake manifold much easier as there is better access to the nuts on the inner studs, and it got the rear float bowl out of contact with the steering column which was always a bear when pulling/replacing the carbs and manifold as a unit.

Also there was the promise of 3-4 bolt-on horsepower because the Maniflow allegedly had better airflow into the combustion chambers, and who could pass that up. There does seem to be a slight increase in power, esp. at the top end though I had to come down two needles leaner to get it. This seems contraindicative: More air yet less fuel, but that is what was proven during several sessions on the track.

These are my "main" HS6 carbs--the spare set I have for sale are equally as nice and are brand new but come with the MG AL manifold. Contact me if interested.

 

[Randy Forbes]

Michael, not <span style="font-style: italic">really</span> directed at you, just to point out what I believe the intended purpose of those ports to be. I'm not saying that they can't function as a balance pipe (or didn't intend to sound that way if I did).

But, if an engine required a balance pipe, surely the carburettor manufacturer would've relied on the engine manufacturer to supply it; aka, the intake manifold.

I'll admit that my exposure to SUs has diminished considerably over the years, but I did order a set of the "new" replacements for one of my MGBs perhaps ten (10) years ago. While I thought I was ordering the pre-68 versions, they did in fact have those same emission intake ports, used to siphon off the crankcase pressure blowby back into the intake tract for incineration.

In my case, I had some dozen or so MGBs sitting around to root parts from, so I could easily set up the post-68 (partial) emissions system to use the ports effectively.

On the other hand, the original poster could block the ports with plastic vacuum plugs, or remove the tubes completely and use lead plugs. But since they do exist, why not use them to vacuum off the crankcase gasses from the rocker box?

 

[GregW]

Hi Randy,
I got this off SU's site. I think #15 in the diagram is what you're referring to.

 

[Randy Forbes]

Yep, that looks just like it. On the Bs, the lifter galley cover has an oil/mist separator (gauze) built into it, plus you can see the elevation difference, so sucking up licquid oil wasn't a problem (no matter how bad the rings were).

I don't know, if it were my setup (on a Big Healey), I'd probably give it a try. At least the oil vapor would be going into both carbs equally, instead of just the rear one.

 

[Steve Huneck]

Thank you gentlemen - If I have this straight, I believe I can just connect the carbs together and get back on the road. Another option is to re-route the hose off the rocker valve cover from the rear air cleaner to a 'Y' connection connected to both carbs. Please let me know if I have misunderstood anything.
Thanks,

Steve

 

[GregW]

Hi Steve,
I would be tempted to do the Y adapter first, remembering to cap off the air filter once you've moved the hose from the original fitting. Second would be to just cap off the carb fittings.

 

[Johnny]

Hi Steve,
I would be tempted to do the Y adapter first, remembering to cap off the air filter once you've moved the hose from the original fitting. Second would be to just cap off the carb fittings.

Greg, do you think this would be a good time to put a PCV valve inline with the Y adaptor?

 

[Randy Forbes]

Hi Steve,
I would be tempted to do the Y adapter first, remembering to cap off the air filter once you've moved the hose from the original fitting. Second would be to just cap off the carb fittings.

Greg, do you think this would be a good time to put a PCV valve inline with the Y adaptor?

It would be the perfect opportunity.

 

[Steve Huneck]

Gentlemen - I have just heard back from SU and they stated that for my car the brass tubes should have been replaced with plugs, and have asked that I send the carbs back so that they can rectify the problem. But as I live in Canada this becomes complicated and expensive, duties, taxes, freight, food for the huskies, etc. But while I work this out, the 'Y' connector idea has me intrigued. What are the advantages to the "Y" connector/PCV valve set up?

Steve

 

[Johnny]

Steve, as I see it the one advantage is that you're spreading the crankcase pressure and valve cover ventilation over both carburettors, and doing so without "dirtying" up the rear most air filter. Sounds like a good idea to me. The only disadvantage is how do you route the hoses and where do you place the PCV valve?

 

[Randy Forbes]

Steve, as I see it the one advantage is that you're spreading the crankcase pressure and valve cover ventilation over both carburettors, and doing so without "dirtying" up the rear most air filter. Sounds like a good idea to me. The only disadvantage is <span style="font-weight: bold">how do you route the hoses and where do you place the PCV valve?</span>

Using Greg's illustration as a guide, connect the side cover port to one (1) side of the "T" atop the rocker cover, as original. From the other side of the "T" run a suitable length of hose to a generic PCV (root through the "HELP" product line at your local auto parts store to find one with appropriate hose barbs). From the side of the PCV that you can suck air through (but not blow through) run another short piece of hose to the "Y" adapter, and then to each carb.

From the "T" to the "Y". you'll undoubtedly need to transition the hose size smaller, so be creative, keeping a streamlined appearance in mind. Idealy, you would find a PCV with different size barbs (on the correct ends, of course) and likewise, transition smaller at the outlet of the "Y" adapter. If you're good with tubing and can weld, you'll arrive with an elegant solution all your own (but be prepared to fend off requests for more, once word gets around).

EDIT: I forgot to mention, use ONLY rubber hose intended for emissions system, as it is a smaller wall thickness (neater looking) yet still impervious to oil liquid and vapor.

 

[Steve Huneck]

Thank you very much, I think I'll give it a try. I have a feeling it is not quite right now anyway. Currently the hose runs from the crankcase to a T, where one side attaches to a non-terminated hose, the other side goes to the valve cover and then on to the rear air filter. So, off to the parts store. Thanks again.

Steve