Lean on 12psi and over
Turbo Mini Forums

With the lovely weather at the weekend, I got the car out and went for a drive...

As with all things turbo I got the urge and pulled over, off came the bonnet and the boost was wound up. The engine has now cover a few huundred miles and I am confident its been run in enough now. So 10psi came, and I pulled over again.....

The boost was upped to 15 psi, but as boost gets over 12psi the AFR goes over 15. The needle is currently a BDD.

The engine spec is;

1293cc
omega 10cc, 1mm below deck
BK450 gasket
MED FIS 31/36, 28cc chambers
GT1752
Avonbar phase 2 cam

I hope its just the needle is way off and nothing else is wrong!


Thanks, Al

im documenting what i am doing with my needle as i go, bdd is a good base needle but as you have found doesnt give alot of fuel up top, i found it to be about 8psi before going lean
so i would say it is the needle
i would also recommend against the avb high boost needle / bca it is way way of in mine at least far too rich

Edited by Brett on 12th Mar, 2012.

Yes i moved to the darkside

Instagram @jdm_brett

I actually moddified the needle slightly whilst at slark with the 998t so that may account for the 12psi rather than 8.

The other thing i have noticed is that it goes lean as you re apply the throttle, its just a little hesitant, and the afr shows 16 some times. Its never been on boost with that happening. its from idle etc. maybe the part lean pipe is the cause of this??

Cheers!

no the lean pipe wont cause this i think,

some engines are happy to be fueled with a standard BDD like mine, i was sort of lucky to dial it in just on the screw it goes that way sometimes

if you havent i would fit an extra spring to the one you have in the carb twined to geather its sort of a frig but works.

you may be able then to get it on the adjustment screw ..........if not you will have to profile it at the correct range on the needle, use a pillar drill and some 600 wet and dry .....go steady though
and try the adjusting srew to dial it in also after modding

best power and where the fun is its ......12.5:1 AFR
hope this helps

Could you not try a base needle of bca iam sure that's just a little richer than the bdd mite be a good starting point & iam sure the avonbar high boost is a profiled bca iirc

Avonbar high boost is a bca, theres a slim chance of there being a needle on the market that will be right, you have to profile your own.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

I found that mine would go lean with the part throttle lean off pipe connected.

Make sure you have enough oil in the dashpot and that the piston moves inside the chamber smoothly.

I recently had a fueling problem similar to yours and one of the above fixed it.

In the 13's at last!.. Just

Be had a BCA in the upside down skip. We put a valve in the part thorttle lean of as it would go lean transitioning to boost on higher boost, but Ok on lower boost. The BCA needle was still rich pushing 25psi down it's throat... still made good power though...

When i get home ill stick up a graph of the bdd, bca and my current needle so you can see how rich it really is i found it very lean on pulling away though

Yes i moved to the darkside

Instagram @jdm_brett

Try this website
http://www.mintylamb.co.uk/suneedle/

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

I need a new needle for the clubby too. BCA is way too rich for it so it seems.

If something is worth doing, it's worth doing half of.

here we are,
these are actual measurements of the needle thickness measured every 3mm
i have searched the entire list on the link benny put up in the past, i have a rough idea of the shape i need but nothing off the shelf comes as close as the BDD i am still leaning out higher up but have a boost creep problem to sort before much more tweaking of it the carb will never read stations 14+ due to the mechanics of it so ignore anything after that

Attachments:

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Edited by Brett on 13th Mar, 2012.

Yes i moved to the darkside

Instagram @jdm_brett

thanks Brett, thats very useful.

I can't fully understand the leaning out with more boost. As the fuel pressure rises to counter act the additional pressure from the turbo - unless the additional air flow needs more fuel than the needle/carb can deliver?


I have ordered a BCA from Somerford today, which i'll try before the rolling road.

I know Richard minivan had a lot of trouble with his BCA and caused more trouble than its worth. but you never know!!

the rising fuel pressure is just to keep the float bowl filling, the needle still sorts out the fueling

Yes i moved to the darkside

Instagram @jdm_brett

Then it's the needle... That's a relief!

Have you seen turbo tels thread on fettling needles? It's a good read ans just shows how many variables there are.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

I am running a standard (BDD) needle with the Avonbar high boost spring (Green?). I also have a valve in the part throttle weakening hose - closing this down got rid of the hesitation as it comes on boost in the low-mid rev range - but totally blocking this hose off made it too rich. The fueling is still not right - I really need to get an A/F guage to figure out what it is doing!

1971 Austin (Healey) Sprite - running turbocharged since 1993
My Car thread: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=448825

Yes i moved to the darkside

Instagram @jdm_brett

Edited by Brett on 14th Mar, 2012.

Yes i moved to the darkside

Instagram @jdm_brett

My car was far to lean on a standard BCA, so I had to file it down loads. Funny how some cars are fine with higher boost on a stock BDD ?

WWW.TURBO-MINI.COM

I suppose there Are So many variables though, engine to engine;

Turbo type, intercooler, intercooler hose diameter, inlet manifold, inlet throat size etc etc.

Be interesting to see what needles the 200bhp+ boys are using...

Edited by almichie on 14th Mar, 2012.

Mine was way to lean with std bdd I've got the avonbar high boost bca & is a bit rich top end but better than being lean plus iam sure when I get the boost set to 15psi it'll not be as bad