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Stromberg Adjustments? Is that even possible?

Posted by elkluvadore 
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max kluver
fort collins, USA   usa
1970 Triumph Spitfire MkIII "BabyCakes"
I'm back, replaced the rocker assembly, she's running strong again, but a test has shown that the Zenith Stromberg CD150 on my 1970 mk3 is running lean (any manual movement of the air valve stalls the car) How do I adjust the mixture to run a bit richer (plus I've got a bit of lack of power on the roads).

stever70 Avatar
Steve Rice
Atascadero, CA, USA   usa
1972 Triumph Spitfire MkIV "Legal Go Cart"
There is a special tool that yo need to order that allows you to adjust the needle fromt top. Has it always run lean? Are yo sure there is enough fuel getting to the carb? Just my 2 cents...make sure that everything else is working before adjusting the mixture.

I love my little "go-cart" drinking smiley

jasz Avatar
Al Jaszcar
Greenwood, SC, USA   usa
1980 Triumph 1500 "Jaz's Spitfire"
Have you kept oil in the carb? Sometime the rubber diaphram inside the carb can crack causing lean running.


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Tom C
USA   usa
You can adjust the mixture with an Allen key. 1/8 inch I think. Remove the dampner from the top. You have to hold the air valve with your finger so it doesn't turn also.

If it doesn't improve, you may have other problems with air getting past the bypass valve, or temperture compensator causing it to run too lean.

90632D Avatar
Fox Trapper
Various, USA   usa
Biggest problem with the ZS is the emission circuit on the carburetor. Essentially, it's a very large controlled vacuum leak. Easily and frequently screwed up, in which case the runs badly. I'd suggest starting there. At the least, close it off, and bring components on it back into trim one at a time. Lots of gee-gaw do-dads there, take your time.

Float level makes a big difference. Makes a big difference on just about any carburetor, but it's a really big deal on the ZS and SU carburetors. Use it as a tuning tool to adjust total mixture bias. I've found raising the float level up just a little makes a goodly improvement many times with a ZS.

Beware the needle shape. Especially if you happen to see that it's not the stock needle. These cars are old, and many has had a carburetor swapped, and now has a needle that's just not very good for the application.

And there is of course the needle adjustment. Which is backwards to an American. Screw it down to screw it up, screw it up to screw it down.

cokerart Avatar
Bob Coker
Atlanta, Georgia, USA   usa
1973 Triumph GT6 MkIII "Spit-6 Or Dr. Frankenstein"
All the advice listed above is good. The float may be too low (Usually it's too high, but hey...) but you can adjust that fairly easily if you remove the carb.
As well, if the needle is bent, you could have an issue.
The ZS tool is critical for dialing in the mixture. You can use an allen wrench, but you'd have to remove the vacuum bell to make the adjustment. With this tool, it is done with the bell on.

Gerry Adams
Lincoln, Nebraska, USA   usa
I am having similar issues with the original water cooled Stromberg on a newly purchased 1978 Spit. It started well but ran with backfiring when I got it. First thing I did was take off the carb and put on a newly rebuilt one (also water cooled). No change in performance. Then, I color tuned it and wow, it ran great.

BUT, now I need your help!
If I adjust the idle to 700-1000 when warm, it just won't start in cold weather. If I adjusst the idle and throttle for cold idling, then it races at 3000rpm when warm.

Also--if you adjust the carb using the TOOL (I have it) should you again Color tune it immediately following?

I am trying to keep the car original but I do have a manual choke Stromberg that work great and so I am fighting temptation to swap!

90632D Avatar
Fox Trapper
Various, USA   usa
Did you carefully study the baffling and reversed idle speed and high speed idle adjustment? It's not as clear as it seems. The obvious idle adjustment, isn't.

Gerry Adams
Lincoln, Nebraska, USA   usa
I'm back to reading the Haynes manual. You're response made me realize I was using the wrong adjustment for the idle. Every stromberg is so different that i do get confused and one water-choke has the older temperature compensator, while the other one (stock) has the white plastic housing over the fast idle screw. They don't have comparible idle screws. I hope i won't have to make adjustments inside the water choke jacket.

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Paul Rezucha
Alameda, CA, USA   usa
Can anyone tell me where to buy the adjustment tool. I saw it once someplace but cannot find it again.

Dickie B Avatar
Dickie Brewer
Clover, South Carolina, USA   usa
1973 Triumph Spitfire MkIV "Rose"
1982 Chevrolet Corvette "Buddy"
1991 BMW 850i "Rocket"
2005 Nissan Frontier V6 "NIZMO"
VB has it.

cokerart Avatar
Bob Coker
Atlanta, Georgia, USA   usa
1973 Triumph GT6 MkIII "Spit-6 Or Dr. Frankenstein"
Everybody has that tool:


SpitBits (Item #33)

TRF (Item CAT1)

Rimmer Bros.

James Paddock, Ltd.

Anthony Kurilla
Las Vegas, USA   usa
1978 Triumph 1500 "Wiggles"
1996 Ford Ranger Pickup "Theresa"
I just leaned out my carb as my plugs were mighty sooty. I got the tool and was surprised how much I had to back it off to stop the soot from forming on the plugs. I have no idea what was going in the PO's head cuz it was so rich running. I am going to run it for a few days after work and see how things seem, but so far things are much better.

1978 1/2 Spitfire

Paul Rezucha
Alameda, CA, USA   usa
Good to know! Did your car run much better? More pep? Mine, as is, does not have too much pep. I should get the tool in a couple days and try it! Thanks!

Anthony Kurilla
Las Vegas, USA   usa
1978 Triumph 1500 "Wiggles"
1996 Ford Ranger Pickup "Theresa"
Mine had pep just hella-bad gas mileage. I hardly drove around the block in the hood cuz I am still not trusting it for longer jaunts. I have had it about a month and it was not even running when I got it. Still alot of work before I will be confident in driving it to work and around town.

1978 1/2 Spitfire

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