How to tune for air filter - Jerking on mid throttle!

[stephenpolhill]

Hi. I bought a cone air filter (K&N style from a mini) for my standard 1098 with the HS2 carburettor. I have fitted it and tried to tune accordingly. It really does pull well when I am flooring it, and she idles well however on mid throttle, ie driving normally, theres small bursts of power and its rather jerky which is enough for me to consider removing it. Has anyone else fitted a cone air filter/induction kit and had this experience or any advice on how to tune.
I would greatly appreciate it

Steve

[mike.perry]

Mark the position of the mixture screw and then try a small adjustment, a couple of flats eitther way. If it does not work you can go back to the original setting. Alternatively it could want a different needle

[alex_holden]

You probably need to change the needle, as the mixture nut only adjusts the mix at idle. There's a program called WinSU that might help you find a starting point.

[MarkyB]

Surely the mixture nut adjusts across the whole range as it alters the relationship between needle and jet?

Only changing the needle will effect the mixture at a particular point.

[chrisryder]

i've found 'minits' a mini specialist, really helpfull with needle selection. i just gave them a call and told them what i'm running and they told me what needle and what spring i'd do best with... i got the needle and spring from elsewhere mind you... but they were very helpfull!

[alex_holden]

Surely the mixture nut adjusts across the whole range as it alters the relationship between needle and jet?

You're right but what I meant is it's difficult to adjust the carb under load without a rolling road, so you normally adjust the mixture nut to get the right mix at a (fast) idle. If you then find that it performs poorly at other throttle openings that suggests the needle profile is wrong.

[millerman]

Has anyone tried emery cloth to reduce diameter of needle where the perceived weaker setting is occurring, if so any tips on how to determine the correct area

[stephenpolhill]

One helpful MMOC member I have been mailing suggested the needle, I just wanted to keep my engine totally original with just an airfilter but I assume that isn't so possible. Also having just seen my fuel bills I think I will pop it in the other Minor under engine restoration we have so that can be messed around with. I can't drive on lighter throttle with the filter as its dead jerky!
It is a shame because under full throttle the noise is stunning! Especially in underground car parks..
I will certainly ask those guys at mini for advice with needles when i get to it so thanks alot for your help!
Ill go enjoy the noise on my way home..

[mike.perry]

The K&N filter is presumably more efficient than the standard unit and lets more air through therefore causing the engine to run weak. This may be more noticable at certain throttle openings.
Therefore my suggestion of adjusting the mixture may well solve the problem and if it does not you can return to the original settings and it has not cost you anything.
The trouble with reprofiling the needle is that you lose the reference point and if you get it wrong you cannot go back.
http://www.mintylamb.co.uk/suneedle gives you needle comparison charts

[bmcecosse]

What oil do you have in the carb damper ? Try some 3 in 1 - but if it's still 'jerky' then try 10W40.

[stephenpolhill]

Damn!. Just got in from changing it. She seems to be running amazingly smoothly now with the original filter on. I think I will use all your advice for the other car ;)