15 replies to this topic

[datsun100a]

Does anyone know of a good guide on modifying su needles? I have searched but only been able to produce the odd vizard comment.

I am running a hiff44 with a itg filter on a 1293 with sw10 cam and mg metro head but I am having serious fueling problems. I have installed a bcg needle, which seems to be the richest I can get and it is still too weak. Pulling out the choke makes it run at the correct mixture but then it is too rich at idle. Any suggestions would be greatly received......

[lrostoke]

try this

http://www.terryhunt...sb/pictures.htm


Although I suspect a rolling road in your case would work out quicker and cheaper. Ideally you need to rig up an O2 sensor so you can see the air/fuel ratio and compare it with needle position.

o2 sensor kits seem to come in around the £160 upwards mark. I was actually tempted fit one just for the bling factor and it being another toy to play with

link wasn't working should be ok now

Edited by lrostoke, 27 May 2010 - 07:09 AM.

[lrostoke]

weird this site seems to convert the link into one that doesn't work

Go to http://www.terryhunt.co.uk

click on mini, then tech tips, then su polishing

[datsun100a]

Thanks for the link. Should have said I have a narrow band lambda fitted with a afr guage. This has been very helpful at telling me I am not getting anywhere......

[Dave33]

I take it you checked float height and piston rises ok?If so is worth making your own if you have the patience to do abit of testing.
sometimes you can spend along time looking for that perfect needle,there are so many of them,and spend alot of money,no 2 engines even with same spec are ever the same.It makes me laugh when i see carbs for sale that are jetted to suit a specific engine spec!
If you have the David Vizard book(if not i suggest you grab a copy),he says you start with a needle taper that you know is too lean ie. a larger needle,then file a flat on one side along the profile,it doesnt matter that its not round as its the amount of fuel thats delivered thats important.It also explains which part will effect which throttle opening,idle and part throttle,midrange and full throttle there is an overlap here of course,you then take a bit off that section and try it(obvoiusly dont go over overloading it till your happy its not too lean).
I had a similar problem to yours on my much modified 1380 in that all throttle openings were ok except just off idle where it just overfuelled,this is where its hardest to set up in my opinion as the combustion is not as easy to ignite due to the amount of air being drawn in,my problems were more noticeable off cam than on.
The camshaft will also have an effect as when its 'off cam 'its very hard to get perfect fuelling.
Mine is a 286 scatter cam with high kift rockers so quite wild,i have never tried the sw10 but its a bit tamer than the 286.
in my opinion rolling roads are only as good as the guy operating them,if its a renowned A series specialist like swiftune or slark then its gonna be worthwile.If they dont have much experience with The A series then dont bother as i know quite a few mini owners who have been to so called experts and they werent very impressed with the outcome.
So either give it a go yourself(worth a go if your this way inclined) or use rolling road that has good rep with A series engines.
Hope this helps you mate
Dave

Edited by Dave33, 27 May 2010 - 11:02 PM.

[bmcecosse]

That BCG needle is way far too rich! A BDL should be near what you need. There must be a problem with fuel flow or carb piston lift! Does the piston rise easily with finger pressure - and fall back with a nice clunk ?

[Dave33]

That BCG needle is way far too rich! A BDL should be near what you need. There must be a problem with fuel flow or carb piston lift! Does the piston rise easily with finger pressure - and fall back with a nice clunk ?

Edited by Dave33, 27 May 2010 - 10:55 PM.

[datsun100a]

Beginning to think it is a fuel supply problem so the carb will come off after mot on tuesday(fingers crossed) If i pull the choke out with the bcg it runs near perfect fueling. The carb has been vizarded but that should not make a huge difference to air flow with a standard mg head. The sw10 cam is very like a 286, if i'am correct so maybe the engine is under carbed but I really doubt it. With all this hassle I am dreading putting on the modified head when it's ready.

[mk1leg]

http://www.terryhunt...sb/pictures.htm

[lrostoke]

Is there an echo on here I posted that in the first reply, looks like for some strange reason this site changes the words in the link , so you'll find that link doesn't work.

I posted how to get to the page way back in this topic.

[Dave33]

Beginning to think it is a fuel supply problem so the carb will come off after mot on tuesday(fingers crossed) If i pull the choke out with the bcg it runs near perfect fueling. The carb has been vizarded but that should not make a huge difference to air flow with a standard mg head. The sw10 cam is very like a 286, if i'am correct so maybe the engine is under carbed but I really doubt it. With all this hassle I am dreading putting on the modified head when it's ready.

your motor is definitely not undercarbed if its a hif44,it would probably be easier to set up with a smaller carb.
With regards to the Vizard mods,this will make a big difference fuelling wise,did you do them yourself or was it already done?
What exactly has been done as theres simple mods like streamlining the butterfly and shaft to more extreme stuff like squaring off the bore and streamlining the bridge,if the bridge has been altered this is only designed for circuit racers as you have to run very rich down low so no good on road.
Have you checked float height is as should be?
Let us know and it will help us to help you.
I take it the cam was timed in with a adjustable vernier and not just lining the pulley marks up?
DAve

[datsun100a]

Carb was already done, butterfly shaft and bridge streamlined. Got it set up for mot yesterday so not going to touch it till mid week. Just got the dizzy back from ML so will fit it and examine float height once it passes mot. Was very impressed with the sw10 for emissions, 0.7 c/o2 and 650 hc, just need the brakes to work properly and it should pass on tuesday.

Cam actually timed in perfectly dot to dot, I have off set keys but didn't need to use them. I checked and rechecked it several times as I have never had an aftermarket cam line up dot to dot.

[Dave33]

Carb was already done, butterfly shaft and bridge streamlined. Got it set up for mot yesterday so not going to touch it till mid week. Just got the dizzy back from ML so will fit it and examine float height once it passes mot. Was very impressed with the sw10 for emissions, 0.7 c/o2 and 650 hc, just need the brakes to work properly and it should pass on tuesday.

Cam actually timed in perfectly dot to dot, I have off set keys but didn't need to use them. I checked and rechecked it several times as I have never had an aftermarket cam line up dot to dot.

Bridge streamlining will effect the fuelling alot,this basically cancels out the the 'pump jet action' of the su carb design ,you need to run a very rich mixture to achieve no flat spots at low revs and throttle openings.
This is probably causing alot of the running trouble,if you pull the choke out its runninig rich and this is helping a bit.
This is really an out and out race car mod where it wont matter about running rich down low.
Thats good the timinig lines up,but you can advance the timing up to 4 degrees to get better driveability and bring it 'on cam 'sooner withou losing any top end.
Best just to try it and see how it goes.
Are you using the high lift rocker gear aswell?
is your car using a cat?As emmisions can be up to 3.5 co before 92 without cat, .7co is well lean if no cat.
Have you also checked for any air leaks as this will cause the revs to drop slowly?
Hope this helps mate,but im thinking if bridge has been messed about with this is gonna cause you a big headache to set up for road use.
Dave

Edited by Dave33, 29 May 2010 - 06:23 PM.

[mk1leg]

Is there an echo on here I posted that in the first reply, looks like for some strange reason this site changes the words in the link , so you'll find that link doesn't work.

I posted how to get to the page way back in this topic.

Echo...Echo whats whats that that.................

[datsun100a]

Thanks for that dave. car is only for playing with in my old age! lol

no cat fitted as the car was spi and i removed all that gubbins. will play about a little more before i give in. I like your idea of advancing the cam timing a little so might have an extra winter job......

just running normal rockers heard too much about the 1.5s putting extra strain on the cam.

mot over here lets us have 3.5 co, my old 98 mpi with a highly modded engine and not a cat or injector in sight passed every year. Even though are mot is the same as the rest of the uk we don't suffer the lambda test, not yet anyway!