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MG MGA - HS6 Carbys..what needles?

I'm running HS6 carbs on my Oselli 1950cc engine. Can anyone advise on what needles I should be using? I'm not sure what the standard needle is, but it seems as if the engine is running very lean (pinging on load). BTW, it is not the timing...this has been fully checked out.
Gary Lock

Another thing to consider doing is putting in stronger springs.
A Bowie

Gary,
How do your current needles compare to those used on the twin cam, which used the same sized carbies?
Mark Wellard

Looking at the MG special tuning manual, they recommended SY 0.100 needles and light blue springs.
A Bowie

Gary
Don't get caught out putting heavier springs in to cure this, you'll lose any advantage of having the 1 3/4" boys
The SY needles combined with the light blue springs are a good all round choice
I have used this combo a few times and they really do work well-----
examples-----
1800-.030" over-big head, big cam, ramtubes ,no airfilters, fairly free flowing exhaust
result--mixture pretty well spot on but with big bore lcb manifold and short ,out the side exhaust it went borderline lean but ok
--
1950--big head and big cam, ram tubes with big sponge aircleaners, big bore lcb exhaust with big bore muffler and pipe out to the back-----result---almost perfect mixture everywhere
---
1974cc---same spec as above basically
result---good strong mixture everywhere but maybe just a tiddle on the rich side on absolute full hook at the top end of the rev scale---but---these engines tend to like it a little on the rich side when you're working them hard over a longer period so ok
------
Mt two bobs worth would be---on your 1950 the SY needle-light blue spring combo, will be good--but--If you are intending to run air filters, make sure they are nice free flowing ones and a decent size and make sure you have a nice big free flowing exhaust. If either of these aren't up to the job the SY's/L.blue --could--go a tiddle rich
But still a good safe combo to start off with---they are a good choice
Cheers
willy


William Revit

Probably not a welcome comment - but why are you running HS6 carbs on a 1950cc engine?

HS4s will give better torque (cos of increased gas speed and hence atomisation) and won't strangle the engine at WOT unless it is producing over 140 bhp.

Chris at Octarine Services

Thanks for all the advise.
Chris..because I had a brand new set given to me!
Gary Lock

This is worth a read.

https://www.bookdepository.com/How-Build-Power-Tune-SU-Carburettors-Des-Hammill/9781903706749
A Bowie

Gary how did you get on with this?
A Bowie

Andrew, thought I'd try and get the book you mentioned, but not at over A$140.00! All of the "experts" around the globe say that the standard BBW needles should work fine. I'm about to start playing with the dashpot oil thickness, trying 20W for a start.
Gary Lock

https://www.abebooks.com/servlet/BookDetailsPL?bi=22498617198&clickid=QKA1z-yJox8h0sx3VgXFj1WGUkmxF8UM9wmBww0&cm_mmc=aff-_-ir-_-259877-_-77416&ref=imprad259877&afn_sr=impact

Updated version; $30
A Bowie

Gary, BBW needles and 6 carbs !! I'm running those on my 3.9 V8. Giving 200+BHP BBW is classed as a "Rich" needle for the 3.5 even. SY are even richer!!
You need to get on a rolling road and get the fueling checked out throughout the rev range, it will be money well spent. Guesswork costs a lot in needles, as well as time especially if you start polishing your own. Thickening the oil only slows the piston rise. The damper is there to give the fuel chance to catch up with the lighter air when you press the throttle it doesn't affect the mixture otherwise.
Allan Reeling

Allan
BBW would be ok on a 3.5 for sure but way too lean up in the revs on a 1950
Gary
Dashpot oil only comes into play during low speed acceleration
If you put thicker oil in to overcome a lean situation it will only fix it at low speed,
It will still be lean up in the revs where things melt
Be safe--
SY and blue springs--Make sure you get the springs-Your carbs have probably got red fitted which are too heavy for your application-It will go like a jet-and will either be right or a little rich depending on your setup but a good safe starting point
Lot cheaper than a new engine
willy
William Revit

Willy,
Would it not be better to start with BBW then, and polish them towards the top end of the needle to match the SY? But would still get on a rolling road!
Allan Reeling

Allan
Yes and no -- A lot of fiddling and measuring to file them down and match them when you can just buy them, they're readily available and not expensive--he'll need springs anyway
I don't know what needles Gary has, but if he has to go and buy some it's better to err on the safe (rich) side ,get some results and and work back from there
100% agree with rolling road tuning for needles---saves a lot of trips up the road
If Gary's car is that lean that it pings, it's got a very short life ahead of it if it doesn't get a heap more fuel into it
These motors tend to perform better with the mixture really strong in the top half of the rev range when being worked hard
willy
William Revit

This thread was discussed between 01/08/2017 and 15/08/2017

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