Hi all,

Just after a couple of ideas on tuning my engine:
1098 with approx 10:1 CR
Modified 202 head with bigger valves
I’d estimate it’s probably making 75hp
Innovate wideband with exhaust tip sensor

So I started with:
Used Red springs
Used M Needles
Penrite SU damper oil

With this it was way too lean at cruise (15-17:1) and also too lean under throttle (14-15:1). I added a couple of flats on the jet to make it richer, but it was still way too lean overall.

I then changed to a new AH2 needles. Now under throttle it’s perfect (13.5:1 dropping to 12.5:1) but still having issues with the cruise being too lean (15-16:1) and is a bit rough. I added a couple of flats richer on the jet, which brought the cruise to an acceptable mixture where it was driving smoothly, but this made the idle and full throttle too rich.

I’ve done a heap of reading up and came up with a couple of options but wanted some feedback as it gets expensive trying needles!
Needles richer at the bottom end but similar at the top to AH2 - I think #3 looks like a good choice?
Change to heavier yellow springs

Any other advice is welcome!

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Download winsu Great program to compare needle profiles

It doesn’t work on apple computers by the look of it.

All the other needle combos suggested by Vizard for a tuned 1100 are all leaner than what I’ve got now

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Get it in on a mates pc Dont trust its suggested needles for engine build , but the compare needles is real good

I have a very old SU Midel catalogue that lists "Popular Performance Applications" including Mini 1100 with 2 X 1 1/4: D6 (rich); D3 (std); GV (lean); blue spring.
Austin Healey Sprite Mk3 (1100cc) used AN (std) blue spring.

Is the damper oil really necessary? I have found good old SAE 30 grade was fine.

Thanks Bill. They’re all much leaner than the M or AH2

The #3 is listed as 1071 Cooper S rich mixture and looks a bit richer in the zone I need.

I’m just a bit confused really as these needles are normally used on a 1275 Cooper S and they still aren’t rich enough for my engine. Perhaps the air speed is less through the carb and therefore not sucking enough fuel during the cruise conditions



It’s listed as ISO68 or 20W. I don’t have any SAE30 and I could get this from the local parts shop

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Hi Timmy

I think the change to a heavier spring is worth a shot (keeping control of your revvy motor)
I ran #3 needles in twin HS4s in a mild 1275 and they worked well- but it ended up slightly better with 6's. Keep an eye on your AFR when in Wide open throttle for a long period ( > 30seconds). - watch for slow leaning out just when you don't want it.

Try number 4 I wouldnt change springs at this stage

When ya got cam like 296 and head that was done stupid to impress The motor has little vacuum and the jet needs screwing way down just to idle.Then you take off just above idle and it goes way too rich with 4 CP4 MME BG .Put AH2 in and the off idle richness is gone but the motor needs the BG or MME up top .And the needle you need dont exist.DB went close

Thanks Ian, a generous member has offered to lend me some needles including an AJ, and HV3. These look to be a bit richer at the bottom end where I need it, so I’ll give them a go next and see where we go from there.

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Mine are HS4 . The bigger carbs just made my lack of suction worse . Just remember when you move the jet/ needle it affects everywhere . You can dump more fuel in at open throttle power and it wont matter as much.The bit coming off idle is very tricky to get right.
I got micrometers , a drill and 1200 wet and dry and ended up with BF profile that got close and it still has a bit of a lean spot that i havent fixed. Its over the top as a road car but it can be fun .You have to be a mad scientist lol

I've found a yellow spring is too heavy except in hs6 sometimes.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Kev I put the triples off a 202 XU1 onto a 186 torana Being a bigger motor you would think would run rich nope .
It ran lean from the lesser sucking effect That motor had like an RE13 type cam and a sensible modified head.
The heavier springs or oil hold the piston down so that the suction effect on the hole and needle is greater.