Later SU carbs

[JohnW]

My TC has a later pair of swing needle 1 1/4 SU's fitted by the previous owner and I have fitted K and N pancake style air filters. The engine runs fine when it has got up to full operating temperature but until then it needs choke and is inclined to spit back through the carburettors. The mixture is set up using a colourtune and the carburettors are balanced and when fully warmed up runs sweetly. I have richened it up a couple of flats to try and stop the spitting back and it has improved things slightly which is leading me to think it may have the wrong needles fitted. Anyone know what needles should be in the later SU's and are they the same as fitted to the earlier models?

[Tom Lange, MGT Repair]

I believe you need ES needles; slightly richer ones are EM needles. Bew sure your floats are properly adjusted; I still use the old 7/16 adjustment, and it has alway been OK.

Tom Lange
MGT Repair

[Duncan M]

How does it run with the K&N filters removed? I have heard a number of tales about how the H2's do not like K&N filter media because they restrict air intake. Only pancake filters I have ever run with H2's are some vintage Hellings and Stellings with the original perforated steel outer and inner and bronze steel wool type material that gets cleaned and oiled accasionally. See pic. No restrictions with that original media design.

thumbnail (5).jpg (52.95 KiB) Viewed 2244 times

[Steve Simmons]

Do both carbs act the same? It does sound like they may be a little lean. Also have you double checked the timing and valve adjustments? I'm just shooting in the dark of course.

Duncan, those filters aren't rare but that sticker sure is. There are hot rod guys who would give their left arm to have the real deal with the sticker on it. I have a set also, in pretty decent condition. I'm not using them though, so I'll probably sell them off at some point.

[Duncan M]

Steve- the decals are neat, but the real treasures are the intact elements. Those are almost always missing, or toast. Very well made.

[JohnW]

Do both carbs act the same? It does sound like they may be a little lean. Also have you double checked the timing and valve adjustments? I'm just shooting in the dark of course.

Both the carburettor pistons drop the same. I will warm it up and check the valve clearances and check the timing so that can be ruled out and report back, thank you.

[JohnW]

How does it run with the K&N filters removed? I have heard a number of tales about how the H2's do not like K&N filter media because they restrict air intake. Only pancake filters I have ever run with H2's are some vintage Hellings and Stellings with the original perforated steel outer and inner and bronze steel wool type material that gets cleaned and oiled accasionally. See pic. No restrictions with that original media design.
thumbnail (5).jpg

It runs far better with the K and N's than it ever did with the standard factory fit filter (maybe this is because it has later SU's fitted?). I have kept the origonal filter so the next keeper can put it back if they so wish, personally I like good air filters having seen the damage dusty air can do to an engine.

[JohnW]

Have just checked the valve clearances and timing and all is good.
Also have spoken to a very helpful chap from Burlen ( the SU people in the UK) and he informs me that the V3 needles I have are not the spring loaded type but have been adapted (a very common thing to do evidently), they are also the wrong ones for my car. He said I need ES needles (as Tom also said above) and some adaptors to make them fit my carbs.
These parts are now ordered so we shall see how things go when the bits arrive and are fitted.
I wonder how many more things wrong I will find with this car?

[Duncan M]

What do the plugs look like? Did the car come from high altitude? If it runs better with K&N pancakes then you probably have the lean needles. You may end up with the correct richer needles and doing away with the K&N's.

[JohnW]

The car didn't come from altitude, Belgium is pretty flat. The reason it runs better is because the origonal air filter was rammed full of steel wool .............. and I mean rammed, the poor engine was so starved of air. I fitted the K and N's because I have a thing about good filtration and there is no way an origonal type filter would keep out tiny particles of dust. I have seen engines wrecked from poor air filtration and these days there is no escuse for not using good filters (just my opinion).

[Duncan M]

John, as I said early on, most people have found the K&N pancake filters to be overly restrictive in the H2's on the XPAG engine. When you get the correct standard needles it will probably become obvious that the K&N pancakes are no good for this application. Using the K&N pancakes with the standard needles will probably result in an overly rich mixture, because not enough air is getting in, in proportion to the fuel. Note that the Stellings filters I showed above are probably twice as "thick" as your pancakes, and yet the bonnet closes properly without hitting them- on a TC. Only solution is to find filters that do not restrict- and are not foam (good luck) or convert the original air filter housing to accept a modern paper filter. As in the resources section of this site-
http://www.mg-tabc.org/library/T-air-cleaner2.htm

[stephen stierman]

In the technical section is an article about fitting a replaceable paper air filter element to the standard air filter cannister. The instructions are quite clear and the number of the element is given, it fits a Porsche 912 and perhaps a Chevy Vega as I recall. I have done this to my cannister and it works fine and looks right. http://www.mg-tabc.org/library/T-air-cleaner2.htm