Help with carb needle selection

just wondering if anyone has a similar spec to my recent project
3.4 mk2 bored to 3.8. using a B type head ported/polished. inlet manifold polished and carb flanges bored for 2inch carbs. Rob Beere mild camshafts
using HD8’s with 125 main jets with UM needles thermo starting carb. 3.77 diff (car has O/D). free flow 2inch exhaust. no air filter at this point
car starts and runs and it really wants to fly but it runs out of puff round about 3500 rpm. I have richened the mixture to where im about 3.5 turns down on the mixture screws and it has improved things but its not 100% as I can feel the car hanging back.
im tempted to try different needles but not sure of the next needle step. I feel a jump to UO is to drastic but not sure of an intermediate step. would like to hear from anyone with a similar setup
best regards

I had a 420 that did that. I too was running no air filter.
I asked here, and was advised to put the whole filter system back on. Fixed!
It was something to do with the suction over the jet. I think the MKII has a similar filter set up.
Good luck, sounds like a beast!


Go onto the Minty Lamb [or mintylamb] web page and you can compare your two needles with other profiles ,
if you are running out of fuel at higher revs a thinner needle is required from half way to the point.

I had the same kind of trouble , after fitting HS8’s , spent a lot of time setting up the carbs , revved up and tick over was spot on , but on the road it was a pig .
So like you I was adjusting the mixture screws .
Problem is we are more or less guessing what we are adjusting them too !
You would be very lucky if both your SU’s are happy with the same adjustment .
I got a colour tune , it takes the guess work out of what mixture you have !
I was surprised how much mine was out , but the car was running ok
I check it about once a year , engine pull’s like a train :sunglasses:

So did you stay with the standard needles for the 4.2?

With best regards

My Mk2 hsa a 4.2, with straight port head and 2x HD8’s. Free flowing exhaust (1.75") and a custom air box that draws fresh air from under the fender.

UM’s were too lean because of the increased flow, I went to UB’s. They seem good to 4k (that’s as far as I’ve pushed it) though my rear carb is 1 pt leaner than my front carb so that’s kind of annoying.

I have o2 sensors in both pipes to test the mix at idle / cruise / accel.

Many thanks. I have ordered UB’s and UU’s so will give these a try.

With best regards

I found the invoice from Burlen

HS8 needles wont fit HD8

I have BAW and BCC sets for my triple HS8, which are stock for S1 and S2 XJ