Tri-Carb Modification

Austin Healey 3000 Tri-Carb Setup & Camshafts.

This page is intended to give some help to those like myself who are interested in tuning the AH 3000 engine for road use. The information is based on my own research and findings, and neither myself nor the Austin Healey Club UK can take any responsibility for the accuracy of the information, or any consequences of it’s use.

The 3000 engine effectively appeared in four different guises relating to camshaft and carburetor specifications:

AH3000 Model Standard Engine Setup

Model 3000 MKI 124bhp 3000 MKII 133bhp 3000 MKIIA (BJ7) 132bhp 3000 MKIII (BJ8) 148bhp
Camshaft timing 230 degree duration 230 degree duration 240 degree duration 252 degree duration
Carb setup 2 x 1.75″ HD6 (0.100″ jet) 3 x 1.5″ HS4 (0.090″ jet) 2 x 1.75″ HS6 2 x 2.0″ HD8
Needles Std-CV; Weak-SQ; Rich-RD Std-DJ; Weak-DH; Rich-DK Std-BC; Weak-TZ; Rich-RD Std-UH; Weak-UL; Rich-UN
Dashpot spring AUC 1170, Type A-Green, 12oz AUC 4387, Type A-Red, 4.5oz AUC 1170, Type A-Green, 12oz AUC 4826, Type A-Red/Green, 11.25oz

Modified Engine: 3 x HD6 (1.75″) Carbs

The use of three HD8 2″ carbs is well documented, all three having the same needles (UH) and dashpot springs as the standard setup. However, I have not been able to locate any data for triple 1.75″ carbs. In my case, the attraction of this setup was that I already had the two standard HD6 carbs and a set of standard MKII inlet manifolds. These manifolds can be opened out from 1.5 to 1.75″ diameter but no further. Fitting triple 2″ HD8s requires larger, after-market, manifolds.

The following charts my experiments with different carburetor settings, first on an engine fitted with a BJ8 profile cam, then on my second engine with a Denis Welch DWR8 cam; details of which are given below. Both engines have a branch exhaust manifold fitted whilst the second engine also has an alluminium head and Omega forged pistons.

3 x HD6 Carbs with BJ8 camshaft (252 deg.)

Needles Dashpot spring Comments
CV (MKI Std needle) AUC 4387, Type A-Red, 4.5oz Rich low/mid range causing plugs to foul
SQ (MKI weak needle) AUC 4387, Type A-Red, 4.5oz OK but a bit flat in the mid range
BC (MKII Std needle) AUC 4387, Type A-Red, 4.5oz OK
TZ (MKII weak needle) AUC 4387, Type A-Red, 4.5oz Very flat low/mid range

3 x HD6 Carbs and a Denis Welch DWR8 camshaft (278 deg.) (see camshaft data below)

Needles Dashpot spring Comments
BC (MKII Std needle) AUC 4387, Type A-Red, 4.5oz A bit rich, lumpy low range, blackish exhaust
BC (MKII Std needle) AUC 1167, Type A-Yellow, 8oz* Good, most satisfactory combination
SQ (MKI weak needle) AUC 4387, Type A-Red, 4.5oz Good, a bit lumpy low/mid range on part throttle
SQ (MKI weak needle) AUC 1167, Type A-Yellow, 8oz* Good
TZ (MKII weak needle) AUC 1167, Type A-Yellow, 8oz OK, smoother low/mid range, low power
RK AUC 1167, Type A-Yellow, 8oz Feels a bit rich, sluggish
TL AUC 1167, Type A-Yellow, 8oz OK some slight misfire at low speed part throttle. Poor when cold.

* Using a straightened paper clip through the breather hole in the top of the dashpot top and a bit of masking tape to stop it sliding under it’s own weight, a full throttle blast indicated that the piston was reaching it’s full travel with this spring.

In conclusion, I found the BC needle to be best with the BJ8 camshaft, and the SQ needle best with the DWR8 camshaft.

The following chart below gives a comparison of the annulus area for each needle, i.e. the area between the needle and the jet, at each stage of the needle travel. The measurements are equalised at position 2 which is about the idle position. For needle data go to this Triumph site by Teglerizer Engineering

Tricarb needle

Austin Healey 3000 Camshafts:

mm ins btdc abdc bbdc atdc
AH MKI 8.054 0.3145 230 5 45 40 10
AH MKII 9.35 0.368 230 5 45 51 21
AH MKIIA 9.35 0.368 240 10 50 45 15
AH MKIII AEC865 9.35 0.368 252 16 56 51 21
Piper BP270 10.16 0.400 272 29 63 64 28
Kent AH2 10.44 0.411 278
Denis Welch ENG656/7 9.35 0.368 268
Denis Welch DWR8 10.9 0.430 278 33 65 63 31 requires pocketed block & 0.15″ valve clearance
SC Parts SC6614 11.48 0.452 300 50 70 75 45 Requires Webers (note as MGB Race AEH770)