22 replies to this topic

[gdcarpenter]

Thanks for combining. Currently have Red spring, the lightest there is as I understand. Do not know of any rolling road facilities in North Carolina, USA.

[timmy850]

Blue is lighter than red.

AAP to AAC is a huge change, AAC is miles richer than any factory needles fitted to Cooper S 1275 engines.

There are lots of different comparison websites and spreadsheets out there for SU needles

A quick google has found a couple of tuning shops with dynamometer/dyno/rolling road facilities in NC

[sonscar]

Surely to achieve the correct profile you need to know exactly where the needle is in respect to the jet as you drive.Without this knowledge you are randomly guessing at the fattness or thinness of the needle.Steve..

[hazpalmer14]

Surely to achieve the correct profile you need to know exactly where the needle is in respect to the jet as you drive.Without this knowledge you are randomly guessing at the fattness or thinness of the needle.Steve..

Yes theres a good topic on tuning needles yourself on turbominis forum. http://www.turbomini...p=vt&tid=159683

 

[gdcarpenter]

Thanks again to all for the feedback.

For the record this is a 998 not a1275. It's essentially a Stage 1 engine as I understand it.

Genuine Cooper Garages 1989 Anniversary Model conversion installed on a new Mini Mayfair in Japan by the dealer. I am sure it is a stock cam as I measured about 0.225 lift on the rocker arm of cylinder number 1 intake valve on original, hand stamped "Cooper", on CAM 4810 head. Understand it to be a low compression 99H block and compression is 150 PSI accross the board. LCB exhaust.

I will order some blue springs as that should hopefully allow the piston to lift a little quicker which should theoretically richen the mixture.

One poster mentioned that the AAP was used on the Innocentin with a 'Blue' spring so that seems to be a good starting point.

Edit: or should I go with a 'Yellow' spring to decrease lift and therefore increase air speed through the carb to richen things up?

Edited by gdcarpenter, 21 May 2020 - 01:27 PM.

[Ethel]

less lift = richer... excluding the considerable effect the needs profile has. 

 

Carbs work on that there Bernoulli effect, the faster the airflow through the venturi the greater the pressure drop to suck the fuel up the jet.

 

The ideal spring will just allow the piston to reach maximum height at peak air flow with the throttle wide open - that allows as much needle length as possible to be used for varying the mixture.

[gdcarpenter]

Update, and perhaps some of the things I have learned will help express my appreciation for your assistance, or help someone else in need. Some slips ups, some "What Caused That", and some stupid things.

Last night just couldn't imagine the needles being that wrong. Have owned her since February and been through her with a pretty fine tooth comb. No hack work and all signs of being professionally maintained and worked on. Actually in amazing condition for 30 years!

Back to the shop today, and back to restarting from square one and not 'Assuming'. First off I was slack in reinstalling the needles into the dampers, not off by much, but not flush. Tidied that up, but noticed what seemed to be fuel residue inside dashpot!

Out of curiosity went to install dash pot covers and one in particular was not sitting right. A while ago I changed my tappet cover breather away from atmospheric venting. I ran it's vent hose into an air sealed oil catch tank and then onto a tee between the twin carb ported vacuum ports. Seems I squished the hose on tight and I guess that once I removed the dash pot cover the hose end crept in and prevented the dashpot cover from sealing/sitting properly. Tie died that up.

While fiddling there thought accelerator cable seemed way to loose. Fun loosening the tiny hex head cable clamp between the intake manifold runners! Tightened up and then thought to check for full throttle opening - nowhere close -what the hell.

Light came on as I remembered yesterday on run, out of the blue, no throttle control and out of gear engine at what. Killed engine and coasted to side of highway. One of the tabs on throttle shaft between carbs had 'popped' out of the slot on the butterfly cam. I 'popped' it back in and went on my Merry Way but thinking she's not giving me all she has to give. Somehow things got out of whack then and I was only getting about 1/4 throttle travel.

Loosened all shaft nuts and eventually choke shaft 'popped' back to where it should be and throttle had full range. Of course I had to go back and readjust throttle cable with that finicky little hex head locking mechanism. Never enough time to do it right but always time to do it over.

Jets back up to flush with bridge and backed off 12 flats, the whole kabbodle of procedure all over again.
So now with a tiny bit of tweaking here's what I am getting.

Idling around 12.2-12.4, in lower gear throttle smash drops her to about 12.8 , in higher gears heavy throttle drops her to around 13.2, happy, happy, happy! Only catch now is at highway steady state cruising she bounces about around 16, but can hit 17 occasionally.

All in all happy she's pretty much doing what she should. Now figure heavier spring out of the equation as that would make her too rich under heavy loads. Seems that one needle richer should get me as close as I can be, any suggestions as to which needle that might be with that the same top/idle diameter. Seems this would richen up cruising a tad and allow me to adjust idle to being less rich.

Thanks again all and hope this helps someone else at some time.

Would AAQ be the next richness up,,and if so hopefully not too much richer.

AAP 890 855 835 811 788 770 760 750 740 730 720 710 700 690 680 670

AAQ 890 855 827 801 775 754 732 718 701 688 672 655 642 625 612 595

Edited by gdcarpenter, 21 May 2020 - 07:52 PM.

[timmy850]

That sounds like it’s much happier now!

AAQ is significantly richer everywhere, especially at the top end. They aren’t given the naming code in order of richness

There doesn’t appear to be any off the shelf needles that match your criteria of being slightly richer at the bottom end and same up top.