My thoughts as well.
There is a lot more to SUs than where the piston is sitting at a certain time.

I thought I would repost part of my first post to highlight a couple of points.


And I will stress again.....I simply do not have anywhere near the knowledge nor the electronic/computer aptitude to do it.
But I still say it can not be too hard to do.
The magnetic/Hall Effect probably is not the way to do it, however I think SooperDooper Mick could do it. By his history of posts, he seems to have the knowledge and gumption for it.
I am more surprised by the fact that given the everlasting fondness that people (me included) have for the SU that this has not been done before.

My car runs twin 1.25s and I also have couple laying about so I can work that out.
So if a bell needs modifying, all one would need to do is run the modified bell
and its mated piston to determine the needle and then switch back to the original bell and piston.
The big advantage is that everytime you make a small modification to the engine eg change airfilters,
new exhaust, switch carbies or even change location or any little mod
you can very rapidly find the exact tuning or determine whether the mod was effective, without going to a dyno.

I would guess that it has not been done because it won't work.

Morris, you know and I know that is not true. By way of example....
How long has the shoe been around......a thousand years..maybe longer?
Did you know the left and right shoe was invented only a 120 years ago.....
so why didn't they do it earlier? Left and right doesn't work?

Twenty years ago velcro was going to replace shoe laces....

The height of the piston and the amount of fuel entering the engine are related but not fixed. You can have the piston all the way down and be very rich at the exhaust, changing the needle will not fix that. It is the way it works.
All you will find when you try to map it onto computer is that the SU is not a very accurate way of getting fuel into an engine.
You need to log temperature of both the engine and outside the car.
You need to log air pressure.
You need to log revs vs piston height.

There is too many variables for it to work the way you thing it will.

Nevertheless having a computer work it out has to superior then watching a stick through a windscreen.

Computer tuning? Easy! You just need BMC service tool 3718G1708...

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Dave - 64 Nurburg White Morris 850 & 67 Morris Mini Deluxe (Bro's Car)
Previous Rides - 62 Morris 850 (Sold '03 - Now 'Lulu-62') & 76 Clubman S (Sold '99 - SFW-863)
+ Too many other classics

I wanna know what that bloody big wheel did on that computer....

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

It's a twin wheel.....so it's for when you want to go left and right at the same time....you know the feeling

Morris is dead right, knowing how much or how fast the piston rises is only a minor part of tuning, without knowing what the fuel/air mixture is it is a pretty useless bit of info, the mixture is controleed by the profile of thee needle along with the rising of the piston and the throttle opening position, all only control a part of getting it right. The n as has been stated you also need to know the temps and the ignition advance and the RPM, without knowing all this knowing how much the piston is rising is pretty useless, it does not tell you if the mixture is any where near right and the only ways of saying how right it is, a horsepower read on a dyno and a sniffer in the exhaust or many timed runs over a given distance with a mobile data reading setup

I still have an old repco engine anyliser (they forgot to pick it up when I got a new one for my shop many years ago) and pretty much that is what you need to tune cars, it doesn't do the job just lets you know if what you are doing is working but it fails to give you a read of HP so maybe one day I will build a home made dyno, it probably only cost a few hundred $ nothing fancy just a simple roller to load the drive up doesn't have to give any real HP readings just a comparison that its getting better or worse

The tune machines are cheap as, have seen them on ebay for a couple hundred bucks

_________________
Roundies and Clubbies(except vans) are both ugly that is why I have Midas and a van
1293 Mini Midas Bronze,1275 Clubman van

yes it`s all well and good attempting to use a computer to help tune an SU to suit any given engine...

& it`s all well and good attempting to use a computer to sort the correct mixture for your engine at any given rev, throttle position, engine & ambient air temp & ign timing & exhaust length & inlet length & manifold shape, vale timing & vlave lift & & & & & &

OH,,, that`s right,,, it`s already been done

i think they call it an "ECU" & funny enough it`s been fitted to almost all new cars for (at least) the last 15 odd years & theyre even maikng them better & better every day

But the funny part is that i havn`t seen any of those late EFI systems fitted with a carby piston

Strange as it may seem , the people who actually know what they`re doing in the world of automotive engineering , be that mechanical or electrical (or electronic) have deemed the carby piston to be a thing of the past, & is actually detrimental to an efficient inlet system these days,,, the late motor-bike carbys hung onto them for as long as they could, enveloping the piston into their later EFI system in an attempt to smooth the power curve out,,, but alas they gave up on the idea with the introduction of even better computer programs & computer aided equipment

However,,, in saying all that,,, i do feel that there would be some merit in trying to sort this type of "tuning aid" & i`m all for it in fact,,, because lets face it,,, if i could spend way less time tuning a mini,,, & be paid way more for it because i can show a customer how much wizz bang electronic tuning equipment i`ve had to fork out mega bucks for (like that BMC tuning tool in the pic above) then i could totally baffle all my customers into thinking that i actually knew what i was doing & then of course the $465,000 that i can charge them to tune their mini would obviously be money well spent in their eyes yeah???

OH,,, doesn`t it work like that???

Why do people want to have their minis tuned perfectly for the cost of a pie & an iced coffee???

HHHmmmm ?????

I would have though that SU would have created the "perfect" tuning tool for SU carbs,,,, OH!!! they did,,, it`s called --->>>

wait for it


it`s nearly there


ok,,, here it comes


---> knowlege, experience, time & a big bag full of mixture needles, piston springs & magic dampener oil

But hey???? even after all that it the problem ends up being a bung set of points

ok,,, not funny,,, try not to blame me tho, i`m very tired, worked my butt off at speedway all night , from both cars getting smashed up in the first heat,,, complete front & rear ends ends replaced on both cars, mega other crap all stuffed up in the proicess,,, just to have both cars banged up again in the first few laps of the feature race.

some nights we should just kick back, have a drink & not bother racing hey???




I`m off to Byron tomorow,,, hope my surf board doesn`t break

Who`s in charge while i`m away then???

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Please re-read the first post, slowly.

Are we talking about ambient air temp or engine temp?
Ignition advance and timing would only have to be in the ball park to
get the engine running and fine tuned as it needed to be.
RPM.. I presumed that would be a given.
The whole point of this exercise is to devise a better method than squinting
through a windscreen looking at a stick bobbing about.
Oxy sensors have been about for years and are readily connected to laptops. Why not use a sensor to read piston height and connect that to your laptop.
And then have a little program that draws up a needle profile for the car.
Some people are just making it far too complicated.
Thankfully some people are on to it.

That's exactly what I'm trying to avoid, Matt.... exsperience....takes too long to get. "Experienced" just another way of saying "Lots of mistakes"

Sorry to hear you had a bad night, even worse when you really never got started.