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What needle should I be using?
Posted: Tue Sep 17, 2013 8:06 pm
by katy
Car is a ‘61 2 door, engine is a stock 1275 with standard manifolds as shown in the BMC manual, page AA.6, items #154 and 155. The carburetor is an HS2, the crankcase breather on the timing chain cover is connected to a spacer block between the carburetor and the manifold. IIRC there is a 1/16” orifice on the hose fitting.
Currently there is a GX needle in the carb, and I have a spare V3 needle.
Just wondering what would be the optimal needle to use w/this setup.
Not necessarily one of the ones I have, I can order one if need be.
Thanks, Ken
Re: What needle should I be using?
Posted: Tue Sep 17, 2013 9:15 pm
by bmcecosse
The 1275 was never fitted with a single HS2 - it's FAR too small..... It's too small for the 1098 engine also! So I'm afraid you will just need to try what you have, and form an opinion about mixture strength at all the different stages of the needle... I urge you to seek a larger H4/HS4/HIF38 carb - it will run SO much better.....and an AAA needle will then be a good starting point. Are you aware of Minty Lamb?
http://www.mintylamb.co.uk/suneedle/
Re: What needle should I be using?
Posted: Wed Sep 18, 2013 5:27 pm
by katy
Well it runs good w/the GX needle, lots of power, except it seems to be too lean at low RPMs, doesn't like to idle below about 800 RPM. Any idea what the idle speed should be on this engine? I would like it to idle at around 500.
When we bought the car it had twin HS2s on it, and the exhaust manifold was broken with missing pieces. I had a chance to get (not easy in this country) a set of 1098 manifolds w/carburetor, so that's why it ended up with a single HS2.
Re: What needle should I be using?
Posted: Wed Sep 18, 2013 7:16 pm
by bmcecosse
To be honest -a well set up single HS2 is as good as the twins...IF it can be separated from the power robbing hot spot where the inlet manifold is attached to the exhaust. You should be able to get it to idle at 500 - but (sorry can't remember) do you have a breather connection direct to the inlet manifold - to suck away fumes??
Re: What needle should I be using?
Posted: Thu Sep 19, 2013 3:14 pm
by katy
the crankcase breather on the timing chain cover is connected to a spacer block between the carburetor and the manifold. IIRC there is a 1/16” orifice on the hose fitting.
Re: What needle should I be using?
Posted: Thu Sep 19, 2013 3:28 pm
by bmcecosse
Yes - I thought so, that will be drawing air and id probably the reason for relatively fast idle. I doubt it will admit enough air to be causing the weak mixture mid range. But check also for throttle fully seating (is the cable slightly loose) and for air leaks at the throttle spindle if the bushes are worn. You can easily enough richen the mid range mix by simply filing the needle in the area you think is weak. Since it's a single carb - you can just file a flat in the 'weak' area - or if you like spin it in an electric drill and gently apply emery/wet-dry paper to remove a little metal...