Carb needles - AAE vs. AAA

I've read somewhere about the key differences between the two, but can anyone give specifications? I'm running the AAE needles, and I believe I need a richer profile for my intake setup. I have velocity stacks with 4 inch round filters on the end. I have turned down the jets to where there is no sputter at cruise and not too stinky at idle. The lift pins also verify that the mixture is close. Problem is when I get above 3500 rpm the motor seems to run out of gas :( - maybe it's her way of saying I don't need to push any harder and thus prolong her life?!? I get really good throttle response and strong pull from 2000 to 3500 rpm, but it seems like I'm hitting a wall above that. The timing is spot-on - I just rebuilt the dizzy - and the advance curve is close to optimal. I know when you change to a K&N filter it is recommended that you change to a AAA needle. Am I describing the reason why you should do so? Is it in my head or do I make sense?

If your sucking more air you need to go to the AAAs... If your adjust for good idle the the other end will suffer...reverce is the same... AAAs will get you both ends correct.. (if you are sucking more air that is..)

I just realized that a simple search would have answered this question. It's just been running around in my head all day at work and I had to ask... :)

You could probably benefit from using an SU needle comparison program. There are several available, such as WinSU, Paul Tegler's website, or the Excel-based SUSearch spreadsheets (which I wrote and you can download from my website - check Google).

The AAE needle is a leaner needle than the AAA, especially under higher throttle conditions. So the AAE is not the needle for you if your high speed/throttle description is correct. The ABD needle is much closer to the AAA profile, but still a little leaner than the AAA. I tried the AAA needle in my MGB, which does have free flow air cleaners and exhaust. I found the AAA needle to be very good, but a little rich (there are few needles richer than the AAA). The ABD needle was a better fit for my setup (the ADB needle is also very close to the ABD). The stock MGB needle was too lean. Your results may be different - that's part of the fun.

The only real way to properly tune your needle profile is to install an air/fuel oxygen sensor in the exhaust system and use an air/fuel meter to measure how rich or lean the engine is running under various operating conditions for a given needle. Otherwise you must use much more crude seat-of-the-pants methods, which really aren't that precise though they are better than nothing.

I hope you are successful in selecting the right needle for your SUs and have a lot of fun in the process!!

That's exactly what I was looking for Konrad! Thank you!!! I heard you could "roll your own needles" and I may attempt to do just that with this information. I have a spare set off AAE's and a light grinder wheel. This will be fun to do and fun to test. Best part will be explaining my project to my fellow engineers here at work!

Give Joe Curto a call. Provide a discription of your setup and it'll put you in the park.

<<I heard you could "roll your own needles" and I may attempt to do just that with this information. I have a spare set off AAE's and a light grinder wheel. This will be fun to do and fun to te>>

Kas Kasner, former Triumph Competitions Manager, is reputed to have once said, "Any fool can make an SU needle. The incredibly hard part is making two."

Don't try it Brian. A BIG waste of time there.

Look at the actual construction of the needles. They are stepped every tenth of an inch and so very precisely so that you can't even feel the transitions. It is doubtful that anyone nearby has the precision equipment and/or skill to machine a new profile let alone the six dozen that you will need to play with on Saturday afternoon.

A much more interesting and less frustrating way to spend your time would be to use a dynamic comparator such as WinSU and look at the graphs for several needles all at once. Then pick a set or two and try them out. If you make an improvement with them note the conditions (throttle opening, cam profile and timing, engine load, RPM, aid density, temperature, yad, yada, yada) and try to figure out where the needle would be in relation to the jet opening under those specific conditions. If you feel that you could do a bit better with something a little richer at that point find a needle that has a profile that will give that to you at that particular rise position. Vice versa, if you need to go a little lean under those circumstances.

At fifteen to twenty bucks a needle, you can't afford to screw around too much, but the testing and investment is part of the price we pay for such fun. :-)

BTW: It goes much faster if you have access to a dyno and you know exactly what you are doing but that probably isn't in the cards for most of us.

Jack.

Thanks for the comments guys. As usual your wisdom outweighs my youthful enthusiasm! I guess I need to save my pennies for a set of ABD and AAA needles..

For those who really want to do it the hard way, there is a great description of the 'needle altering technique' in "How to Build and Power Tune SU Caburettors" (SpeedPro Series by Des Hammill)

Uses a drill press and calibrated/marked fine abrasive paper.