A new needle adjusts the fuel flow to make the final mixture more rich (lets more fuel into the carb). Since the upgraded air filter setup allows more air into the carb, the needle usualy must also be changed to allow more fuel into the mix to keep the engine form running lean. More fuel + more air = more HP.

According to my Haynes Performance Manual a true "Stage 1" upgrade is generally the upgraded air filter/needle plus the upgraded exhaust (lots of people delete the catalytic converter if one is installed - gives 8-10BHP right there, but you might have emissions problems if your state does yearly testing) and last usually an upgraded exhaust manifold. Some places sell just parts individually while others sell full "Stage 1 kits" with everything. I haven't done one yet on my car, but it's definitey on my list, both for asthetic reasons (the OEM air filter on my car looks awful as does my rusted-out exhaust) as well as performance (I need a bit more HP even on my 1275).

 

If your Mini has 1 or 2 SU carbs, the needle is the ingenious but hard to scientifically tune method used to control the amount of fuel that goes into the engine as you press and release the accelerator.
It is a tapered piece of metal that looks like a big needle (hence the name). As the throttle opens, the needle's sleeve moves to a thinner part of the needle, letting more fuel past. Because there are so many combinations of tapers at the 12 different "station" on the needle, there are somewhere over 500 different SU needles available. Many will make your car run like crap. Some will make it run ok. A few will make it run great.
I have read that the only way to tell which needle with improve your car is with an air/fuel meter, tach and patience.

 

A stage 1 is a bolt-on upgrade, usually a larger carb (e.g. 1-1/2" SU), K&N type cone filter, better inlet and exhaust (e.g. LCB) manifolds, and pipes and muffler box(es) out the back (e.g. RC40). The needle change is required to change the mixture to account for the better inlet air flow. Its my experience that the needle change on top of the stage 1 hardware made a HUGE difference. As I recall, that brings a stock 998 up to about 54 hp.

 

Correct me if I'm wrong, but from your descriptions, it sounds like stage 1 is mainly to help the engine breathe better, allowing it to effectively burn more fuel? So what's stage 2 and 3 like? (I like these educational talks that are on my novice level)

 

There's a program out there called WinSU that will get you in the ballpark. You can also post up your specifications on Minimania.com and folks there will probably offer up a good bit of suggestion.

Stage 3 is usually different carb (or two), cylinder head, etc.

Here are a few for 'ya to take a peek at.
http://www.minisport.com/classic-min...-products.html

 

Stage 2 is a head swap - usually bigger valves - such as 998 head to 1275 12G940 head
Stage 3 is a head swap w/bigger valves and more and/or bigger carbs.
Stage 4 involves cams, cranks, innards.

References: Mini Performance Manual (Mundy) and Tuning the A Series Engine (Vizard)

 

So stage 2 and 3 increase capacity, which means more fuel and oxygen can combust per stroke? Is that right?

How's the cam work?

 

Before you go further down the road to madness, know that Stage 2 and above upgrades really start to get into the big $$. Stage 1 has the benefit of (relative) simplicity and fairly low cost for a noticible performance enhancement (or so I'm told by those that have done it), but as you pass Stage 2, the curve starts to grow steep, indeed.... Just fair warning.

Classic Minis are more about fun, dynamic handling for most folks but like any other machine if you're ready to invest serious resources then you can shoot for equally serious results. If you choose to go that direction, just be sure to document well so we can live vicariously through your check book.

 

1275 period.

 

I had an a/h sprite with a 948 and some upgrades (sidedraft weber etc) anyways it did what I needed it to do and I got around pretty well if I kept the RPMS up. But this was all back roads driving with speed limits from 30 to 45 (tops).

I would recommend the 1275 with a syncro'd gearbox, it sucks to not have first gear syncro'd!!