What is the difference between these two and also to UM?
The UM is the stock needle. Then the UB UE and finally UP in order of increasing richness. All are near identical through the idle stage, M, B and E are similar until about 40% from idle than each is proportionally richer than the one before UP is richer farther towards idle and increasing richness toward the power end. I’ve used them all - Um is too lean, can lead to lean surging at sea level, B and E are similar, you probably wouldn’t notice a difference - maybe at higher rpm, and UP is definitely noticeable in mid range.
Here’s some photos off an online needle chart I use. Hopefully you can see them 
Here’s a handy chart tool you can play with yourself to see different needles:
Im using UE and it offers good power but takes 31/2 turns of jet to idle vs 21/2" book setting’’'are you saying UP offers more mid range power?
Terry,
I am using UB’s in my Triple SUs and they seem fine.
With your experience do you suggest UPs would be best for a standard 4.2 litre configuration??
Dennis
69 OTS
ALL HD8 needles are identical at the idle stations…
2 Likes
Does this match other people’s experience?
I haven’t put many miles on my car, and I haven’t stuck my AF meter on it, but it has UM’s in it, and seems ok.
Where would the lean condition occur…up high, I assume?
Yes. I’ve been recommending UB or UE needles for 15 years or more as better than UM for modern fuel. With UM is is impossible to set mixture correctly at both idle and higher speeds/loads. If set for best idle, it will be seriously lean at highway speed. If set for best highway performance, it will be sloppy rich at idle. UB is better on some cars, UE is better on others. Each car is different.
Good feedback, thank you.
What is the best source for UB and UE needles these days? I assume the recommendation is to get the Burlen brand needles?
A number of people have reported surge on this site. It occurs on my car typically at slower cruising speeds at steady throttle. A lot depends on your altitude, I’m at sea level, and the gas you use. Gas with an ethanol blend is a problem. I know UM’s are lean from testing them on a dyno.
UP needles. It’s rare that you can make a single change to an engine and feel the difference. UP needles are significantly richer in low to mid range, so the torque curve is fatter in the range you accelerate in. I’m not speaking of full throttle, I’m speaking of the type of throttle you give the car as you pull away from a stop, and shifting at 4k.
You will also notice a reduction in fuel economy.
Any comments on UO? I used a set from Joe Curto for years but I put back the UMs recently.
I installed a two channel lambda gauge with fast sensors so that I can finally work this problem with hard data. UM’s are definitely too lean for E85. I was completely blindsided by how poorly they worked, and how impossible it was to adjust them. I expected that if they were just set richer at idle, they’d be fine throughout the range. But no, it’s impossible to set them rich enough. At this moment, I’m running UO’s, just because that was the only alternative needle set I have on hand. The UO’s are actually easier to adjust, but too rich. There just isn’t enough adjustment range to get them above 13:1. But the car really, really likes to run rich. If you haven’t tried a richer needle, you’re going to be surprised.
I’m going to be trying UX’s next, which are slightly leaner that UE’s in the mid range, and slightly richer at the top end.
I installed a two channel lambda gauge with fast sensors so that I can finally work this problem with hard data. UM’s are definitely too lean for E85. I was completely blindsided by how poorly they worked, and how impossible it was to adjust them. At this moment, I’m running UO’s, just because that was the only alternative needle set I have on hand. The UO’s are actually easier to adjust, but too rich. There just isn’t enough adjustment range to get them above 13:1. But the car really, really likes to run rich.
I’m going to be trying UX’s next, which are slightly leaner that UE’s in the mid range, and slightly richer at the top end.
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Where are you getting your needles?
SNG seem to list everything other than the UM as “special order”, Joe Curto seems to have pretty limited stock, and I’m not confident that Moss are selling Burlen needles.
I was originally planning to order them from Burlen in the UK, but the cost of shipping was quite high. I found this place on the web:
They’re in San Diego. Although the price for the part is higher, they ship first class mail. Hopefully they’ll come through with the parts.
Crazy, I’ve lived here all my life, and I’ve NEVER heard of that place. Thanks.
UO’s are a bit leaner than UPs in lower to mid range, but much richer at the top end. Better power at higher RPM, wouldn’t have the fat torque of a UP mid range. They are quite a bit richer than a UE and a bit richer than UB. Their curves are all similar the UO just gets richer and richer.
I never heard of them, either. Never seen them mentioned here or on any other forum. We’ll see.
is there a way to tell which needles are in the car now ?
Hi,
Not sure, but a good dyno and an AFR map from idle to 5.500rpm would tell you how they perform.
Because of change in fuel available (98E5 in Europe) I changed from UM to UB, I bought several sets just in case, but for my ex Ser 1 2+2 the UB’s worked great, the UM’s were a bit too lean with current fuel above 3.000rpm with WOT.
238 DIN HP at 5.200rpm IIRC and ca 230 Nm from ca 1.200 rpm onwards, I did post with pics about this 10 years ago. 
Cheers!
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