Ive recently fitted a fully worked 12G295 head to my 998 (fully ported an polished an increased valve sizes), but i need to richen the mixture as the mixture screw on the hif38 is in as far as it goes and it still wants more fuel. I currently have a AAA fitted and dont know what needle is next up from that on the richer side, so anybody know?
Also, will the HIF38 be on its limits now? Maybe upgrade to a HIF44??
Thanks
Richer Carb Needle Than Aaa
Started by
Iain L
, Jan 22 2011 02:03 PM
4 replies to this topic
#2
Grayedout
-
- Members
-
- 901 posts
One Carb Or Two?
Posted 22 January 2011 - 02:29 PM
Only way to get the ideal needle is a rolling road session where they can tune one to suit your engine exactly. Otherwise you could spend a lot of time guessing!
#3
tommy13
-
- Members
-
- 878 posts
One Carb Or Two?
Posted 22 January 2011 - 03:02 PM
As you may know, SU needles are machined to set dimensions at 12 or 13 points ( stations ) along their length. the first 2 stations are generally the ones in use when the engine is at tickover and these are very similar for almost all needles. I wonder if the butterfly spindle is worn in the body, allowing air to be drawn in?. The float/ fuel level can be checked as shown here,
http://www.sucarb.co...tail.aspx?id=72
There is a needle comparator here which may be of use.
http://www.mintylamb.co.uk/suneedle/
http://www.sucarb.co...tail.aspx?id=72
There is a needle comparator here which may be of use.
http://www.mintylamb.co.uk/suneedle/
#4
Bradfirj9
-
- Noobies
-
- 28 posts
Passed Test
Posted 22 January 2011 - 03:32 PM
You may also want to put your carb mix screw back to the "Standard" setting before trying a new needle, I'm sure someone will be along shortly with that tidbit of info (I don't have a HIF myself, sorry.)
Reason is, as far as I know, the mix screw only really has an effect at idle, the rest of the fueling in an SU carb is governed by the needle profile (please correct if I'm wrong).
Looking at the needle comparator tommy13 has posted, an AAB would seem to be a little richer at the higher stations than your AAA.
On that topic, could someone explain for me if there is any recognizable pattern with the needle names? Do the letters stand for anything in particular?
Reason is, as far as I know, the mix screw only really has an effect at idle, the rest of the fueling in an SU carb is governed by the needle profile (please correct if I'm wrong).
Looking at the needle comparator tommy13 has posted, an AAB would seem to be a little richer at the higher stations than your AAA.
On that topic, could someone explain for me if there is any recognizable pattern with the needle names? Do the letters stand for anything in particular?
#5
bmcecosse
-
- Members
-
- 9,699 posts
Crazy About Mini's
- Local Club: http://www.srps.org.uk/
Posted 22 January 2011 - 04:55 PM
I seriously doubt you need a richer needle - what leads you to that conclusion ? Make sure the needle is set in the carb correctly - shoulder flush with the piston base. As above - the needle choice has no effect when idling, so look for air leaks if it's idling 'weakly'
1 user(s) are reading this topic
0 members, 1 guests, 0 anonymous users
