Does anyone with more knowledge than me care to take a stab at making a recommendation for a needle selection for my street driven Sprite?
Engine Spec is:
1293cc
Kent 276 cam
1.5 roller rockers
12G 1316 smog head slightly ported
Header w/single box exhaust
Pertronix
Dual HS2's w/K&N single box air filter
Fixed or swinging needles?
Is everything else set up correctly Howard? (knowing you i am sure it is)
What springs and needles are you running now?
Stock rich for a Cooper S fixed was M.
The standard needle was an AN, the "rich" needle was an H6, maybe that would be a good starting point? What are you running now?
These are fixed needles. I do not know which needles were in the carbs, as they both broke off as I was trying to remove them. First time I can remember having that happening. I more than likely have some spare 1-1/4 pistons to put into service, otherwise these will have to be addressed on a lathe. I cannot see any markings on the springs either. And for the record, the compression ratio is approx 10:1.
M is the fixed rich needle for a Cooper S and i believe red springs.
Make sure the throttle shafts have no play as HS2's are notorious for wearing out the bodies and spindles and creating air leaks.
Joe Curto is a wealth of SU knowledge and he also sells anything SU. He manufactures an oversize shaft for HS2's saving the body or not having to insert bushings.
His contact information is joecurto.com or 718 762 6287.
Rather then stick with the HS2's, I'd pop a pair of HS4's on it.
Is the consensus of opinion that this engine spec would support a pair of HS4's?
Yes it would. Add yourself some velocity stacks and you're in bussiness.
X 3 With the engine spec you have think you could run HS4's on it.
Don't know if anybody's read this yet - I added some colored text highlights, but the original link is there for those who want the original article.
http://browsemags.com/mini-magazine-may-1-2013/982-su-carburettor-tuning.html (http://browsemags.com/mini-magazine-may-1-2013/982-su-carburettor-tuning.html)
This article has some really great information regarding dampers.
I have that article saved some where, but it is always good to revisit some of the articles.
There are some interesting threads about AFR, SUs and proper running on some of the other forums. While I believe having data is important and I run installed wide bands in two of our cars and have an Innovate stand alone meter, knowing what to do with the data is just as important.
While messing around with the car that has an HIF 44, I was curious where the lifting pin mode of adjustment would place the AFR. While this HIF does not have a lifting pin, I am able to lift it with a piece of wire. It seems when set by this method the the lambda ended up being .96.
I have not had a chance to go back and revisit this and try out the MK1 needle tool.
Terry
I've never had success with lifting the carb piston; it always ends up far too rich for me.
I have been working with the Peter's new MK I Forum SU needle tool, not really new at this point, but still new to me.
I know it has the ability to make suggestions, but I have not got that part sorted yet. The comparison part is very easy.
I need something between a BDK and BDL.
If you file your own custom needles, you'll love the 'Advanced' page.
Here's an 0.090" AAA needle with just a tad taken out of the middle. I typed in some figures in the 'Filed A/F' column until I achieved a (measurable) new dimension. The plot illustrates the difference, and the 'Needle 2 % column' shows me how much I'm 'functionally' removing.
is Rich at the top of the scale or the bottom
On the graphic plot, 'rich' is to the top.
As we look at Needle 1, the first column is the dimensions in tenths - fat end first. Second column is the annular area in sq. thousandths, third column is the comparison of Needle 1 to Needle 2 as a percentage.
The 'Index' column is the needle position number as visualized fat-end up. The 'index' number is also adjustable to the working range of the carb, as SU carbs cannot utilize the entire length of their needles (always have a bit remaining in the jet'), so after position 13 or so, the tip of the needle is just ballast displacing fuel in the jet.
'Needle 2' data mirrors 'needle 1', and the resulting graphs are logically plotted with the fattest position 1 to the lowest left and thinnest uppermost right.
The interesting thing is that if you look at the 'modification' made by filing off/reducing the diameter from 0.0785"at position 4 to 0.0780" (removing 0.0005"), there was a 3.8% increase in annular area - more fuel allowed.
Likewise, removing 0.0015" at position number 6 gave us 7.3% more. Quite a lot! :-\