I bought a '74 Mini 1000 last month and live in Santa Fe, NM at 7,000'. The HS4 SU currently has an AAT needle. I also have an ADE needle which seems to have nearly the same profile. I am predictably running really rich up here.

Can anyone advise as to what needle you are running for similar altitude/engine size? Or have any "formula" for picking a leaner needle? I am looking at an ADN or ADJ but was hoping for some feedback before I pulled the trigger. There does not seem to be a lot of info on this topic online.

Here is how my new baby arrived (the blue one, not the white one!). And what it looked like six months before I bought it - someone else had already gone thru the heartache of doing the metal/rust/paint.

 

Nice Mini! Can't help with your needle choice, but have you checked the mixture? My HS4 has the lifting pin you can push up on to temporarily alter the mixture so you get an idea which way to turn the mixture adjustment nut at the jet.

 

the adjustment nut only impacts idle mix

running mix is determined by the needle

and the only RIGHT way to determine needle is on a dyno and experience

so says MiniWorld for the 10 plus years I've been a subscriber

since finding a Mini smart tech at a dyno place is a wee bit more difficult here in the states as compared to UK

I'd call Seven or MiniMania and talk to them about your specifics .... they are two of the most experienced Mini engine builders in the states . . .

http://www.7ent.com/

http://www.minimania.com/home.cfm

 

I think Capt BJ is partially right, it does affect the idle, but if the mixture (and needle) were right at sea level then since you'll change the starting point of where the needle intersects the jet by moving the jet up or down, it seems to me you've affected the mixture to a degree over the entire range of the needle's travel. I'd lean it out a couple of flats and see how it does first....you may have to adjust the idle speed screw after you do that too. To a great degree SUs are self compensating - as there is less air to lift the diaphragm, therefore it moves the needle less and the mixture is correspondingly leaner....or about right.


like brgpa says, once you've moved the jet up a couple of flats, lift the diaphragm slightly - the idle should raise briefly then drop - if it does that's about right.

 

Dave quotes the basic DIY adjustment plan for any SU

it is pretty much straight out of any of the SU books. I use "SU carburetters tuning tips and techniques", Brookland Books, 1994 edition

It is what they say to do if you can't do it right . . .

But remember, changing something as "simple" as the air filter can require a new needle ....

Call Seven .... what have you got to loose?

 

I use the same book.......and it DOES say that for altitudes over 1800M (5400 ft approx) you will need a leaner needle. I will also say that 7's suggestion for a needle for my engine was way wrong, however my engine was modified so they were just guessing anyway. Unless you have the specifics of this engine (dead stock or modified) all you can do is experiment.


The problem is knowing which one you have so you can progress to the next leaner one.....since you have that info already - go for it. It would be really helpful if you have access to an exhaust analyzer too......other than that you're down to reading the plugs and sniffing the tailpipe


You might post on the 5280 forum (Denver) and see if anyone there has better info too....the Capt and I are basically at sea level.....

 

thanks all; I spoke w/ Ed at Minimania who directed me to Joe Curto (www.joecurto.com); Joe is sending me a slightly leaner needle, AAP. One thing I discovered when I removed the dashpot to see which needle came with the carb (which was brand new, installed by the seller) was that there was absolutely no oil in the carb! I have driven about 15 miles since I have had the car - a reason besides altitude that the carb is acting funny!? I checked fluids when I got the car off the trailer, but did not think to check that . . . .

I will report back when I install the new needle (and dashpot oil) and re-set the carb and timing.

 

Sometimes they also call for a different spring under the dome......

 

I was about to ask if you'd checked the oil in the carb pot .....

the weight of this can make a difference.

Folks use everything from engine to sewing machine oil

I use 3 in ONE

and I take the top end of the carb apart once a year to clean out gunk and ensure the piston 'floats' freely

 

Update; the seller of my car did nice work on the body and paint, but then decided he had too many project and put the car back together w/ a combination of the old parts/motor and some new things. The HS4, alternator and coil are new. But when we removed the plugs, it was obvious that they had been in there for a reaaaalllly long time. Same w/ the distributor - the points are so pitted/volcano that it is impossible to know what the dwell is and the vacuum advance is extremely corroded.

So I have ordered some new items to try to start from zero and get the current 1000 motor running right. In the meantime, we noticed that the jet bearing on the new carb was hanging up at full choke and not releasing when shutting the choke, so I got a new jet bearing and we did a reset on that end, adding a few flats to lean it out - using the existing AAT needle. We also timed it as best we could given the condition of the dizzy. It is running much better now than previously, but I do have the new AAP needle from Curto if I end up changing the needle.

thanks for the help!

 

Pertronix ........