• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)

TR6 Stromberg CD 175 Carb Tuning


Senior Member
Country flag
Another Stromberg question again: OK, I know there has been a ton of material generated on these carburetors but I can't seem to find the answer to my question. I have recently downloaded the buckeye technical information and plan on going through each detail within the next few days. Although my TR6 runs very well, my question concerns the piston lift method of determining rich vs lean settings. With the engine properly warmed, I have attempted to determine if my carbs are running too lean or too rich by performing the piston lift method as described in my Bentley manual as well as other manuals and videos. According to this information as the piston is lifted approximately 1/4 inch, the rpm will either increase (indicating too rich) or decrease and shut-down (indicating too lean). In my case, these carbs always decrease and want to quit when the piston is lifted. I have adjusted each needle valve IAW the manual (turning it clockwise) to enrich the mixture. At full adjustment travel clockwise, there is no effect on the carbs and they continue to decrease RPM and will shut try to shut the engine down. Tonight I tested the car with both carburetors enriched as much as the adjustment would handle (to the full stop) and the car ran well as usual. I pulled the plugs and found normal conditions with a slight amount of carbon buildup at the base and within the threaded portion. I'm starting to think there is something such as an "o" ring that has failed in both carburetors causing this lean evidence. A part of me wants to leave well enough alone and continue to take plug readings but another voice is telling me there is something that is not correct and I had better fix it before I end up doing damage.

This is a freshly rebuilt cylinder head with new exhaust valves. All valves have been adjusted and checked. The ignition system is properly tuned and fresh including wires, plugs and timing. The fuel is fresh with the highest octane I could find in my area (91). The mechanical fuel pump is somewhat new and is working as advertised. The fuel filter is new. There is no problem with fuel flow. What point am I missing?


Yup, 1/4" is way too high. I gave up on the "lift the piston" method and instead went to reading the spark plugs which in itself was a learning experience.


Senior Member
Country flag
Thanks for the help. I don't know why I couldn't find that link earlier but it certainly helps. I'll head back to drawing board later today and re-visit the adjustments.

Geo Hahn

Country flag
There are several methods for assessing mixture - among them the lift-the-pin, examining the plugs & Colortune (viewing the spark). I use all three but in the end rely on looking at the plugs to see how I did.


Jedi Trainee
Country flag
If your carbs are too lean, the car will probably run hot. The best advice I can give you is to leave everything alone when the car is running well. Stromberg CD carbs have a limited amount of possible adjustment and they are very reliable once initially set up. If you just can't keep your hands in your pockets, give the carbs a little shot of cleaner spray every now and then.


Country flag
I think if you put the needles in the middle of their adjustment range you'll be fine.
Put about 300 miles using fresh spark plugs on that setting, avoiding prolonged idling and and trying keep the engine in the 2500 rpm range as much as possible during that time, then remove the spark plugs for evaluating.
That's what I suggest to those who send me their carbs for rebuilding.
Since there is only 1/8" total adjustment range, setting the needles to the middle will make it necessary to deal with only 1/16" in one direction (either up or down) if further adjustment is even needed.
For all practical purposes, the middle is 1 and 1/4 CCW rotations of the needle adjustment screw from fully CW.

Geo Hahn

Country flag
I'll add (because I just went through this) incorrect float height can make tuning difficult. Worth checking if the usual methods don't seem to get you where you need to be.
Similar threads
Thread starter Title Forum Replies Date
L Stromberg 175 cd question Other British Cars 5
R Zenith Stromberg CD 175 float replacements? Triumph 3
M stromberg 175 cd? Triumph 5
M stromberg 175 choke cable? Triumph 2
M zenith stromberg 175 cd Triumph 24
M zenith stromberg 175 cd. Triumph 7
H Zenith Stromberg CD 175 Too rich Triumph 7
Brooklands Air Filter for Stromberg 175's Triumph 3
E Stromberg 175 idle Triumph 2
H stromberg 175 carbs Jaguar 1
S TR6 Stromberg Bypass Valves - Question Triumph 11
T TR6 My '74 TR6 Zenith Stromberg Carbs Float Bowls Leaking Gas Triumph 11
T TR6 Carb Vacuum Port- TR6 Zenith-Stromberg Carbs Triumph 2
M General MG stromberg carb MG 5
Sarastro TR4/4A Stromberg linkage question Triumph 4
SherpaPilot TR6 Stromberg War, Finally Success Triumph 2
R TR2/3/3A Stromberg vs. SU carbs [discussion/advice] Triumph 17
D Stromberg Dash Pot Screws Jaguar 3
Merlin63Tr4 TR4/4A Cracked Zenith-Stromberg float assemblies Triumph 13
steveg Online SU and Stromberg needle database with comparison charting Austin Healey 2
R J-H Stromberg carb connections? Where do they go? Other British Cars 2
R GT6 Carb Floats for Stromberg 150 . Triumph 5
B Zenith Stromberg O ring question Other British Cars 8
K TR4/4A Stromberg..."coupler" that links vacuum outlet to diff vacuum line is N/A? Triumph 3
K TR4/4A Stromberg question. Triumph 13
M TR4/4A Stromberg CD175carb query Triumph 7
RickB MGB Stromberg on my 80 MGB - fast idle this morning MG 6
RickB MGB HS6 or HIF4 bolt right on in place of Stromberg? MG 6
Zimmycobra TR4/4A Zenith Stromberg questions Triumph 13
M TR4/4A Stromberg ? Triumph 4
L zenith-stromberg carbs Lotus 11
P TR6 Tr6 stromberg carb gas leak from starter valve bolt shaft Triumph 5
G Stromberg cd150 question Spridgets 1
TR6BobNF General Tech Midget Stromberg 150 Adjustment MG 8
Airfix Wedge TR8 Zenith Stromberg carbs slow deceleration Triumph 1
W Weber/stromberg air cleaners Jaguar 3
dklawson Early Stromberg Floats - 150CD Triumph 5
bighealeysource Stromberg carb help needed for TR buddy Triumph 8
W Zenith stromberg carbs Jaguar 3
J stromberg float source or x referance Triumph 2
D TR6 76 TR6 Stromberg Air Valve Triumph 2
H Stromberg Carb Sync and adjust Triumph 6
T Stromberg Triumph 22
sundown 175cd stromberg carbs Triumph 4
JPSmit Stromberg Carb Question Triumph 15
R TR4/4A Tr4a, Stromberg float setting Triumph 6
regularman I found the fix for the stromberg on the 1500 Spridgets 6
A XKE Series II Stromberg Carb Upgrade Jaguar 4
C Stromberg carbs Triumph 8
R TR4/4A Tr4a, Stromberg rebuild Triumph 6

Similar threads