Tuning a stromberg 150 CD Carb advice please?

[VYO 372M]

I'm replacing the Solex carb on my Herald 1200 with a stromberg 150 CD carb from a Herald 13/60 this weekend coming but need a little bit of advice.

I've copied the below text from a stromberg manual but am unsure of one point, after initial setting has been acheived, do I still need to hold the air valve down on the bridge in the throttle bore to carry out any final adjustments on the mixture setting using the underside jet or can I just turn the jet?

Stromberg manual text

The idling speed itself is governed by the setting of the throttle-stop screw. While the idling mixture is controlled the jet adjusting screw in the base of the carburetor float chamber and when the idling speed is being set or adjusted these two controls must be used in conjunction with each other. Engine speed is set in the idle position by the throttle stop screw while the jet adjuster determines the richness or otherwise of the fuel/air mixture.

To set the idle speed the air cleaner and damper must be removed and the air valve must be held down on the bridge in the throttle bore. Using a coin the jet adjuster should be screwed up until the jet is felt to contact the underside of the air valve, at which point it should then be turned down again three full turns. By doing this you can establish a working position for the jet.

With the engine at normal running temperature the idling speed should be set by using the throttle stop screw to a speed of 600-650 rpm and by careful and gradual adjustment of the jet adjuster, vary the mixture until the engine runs with a smooth regular beat.

To check the final setting, lift the air valve a very small amount – no more than 1/32 inch and if the engine speed rises appreciably, the mixture is too rich, if it stops the mixture is too weak. If the setting is right, the engine speed will either remain unaltered or may drop very slightly.

Turning the jet adjusting screw clockwise will weaken the mixture, turning it anti-clockwise will make it richer.

Steve

[sprint95m]

Steve, I am puzzled. Is that the instructions for a CD150 or some other Stromberg?
All the CD150s I have seen can't be adjusted by a coin, but need a special tool (which is only a few Pounds to buy).
Said special tool is easy to use.

You can use a Colourtune to set the mixture.
I normally assess the carbs' settings by examining the spark plugs after a decent long run.
It is sensible to renew the carb's diaphragm.

[jeffers]

The early 150 cd can be adjusted with a coin, 1p does me fine. The mixture adjustment screw is set into the bottom of the carb. I have two on my GT6 (even though as MK3 it should have the later 150 CDSE I believe)

I should think just turning the jet should be fine.

Regards
Jeff

[Jon Tilson]

Strombersg come in 2 flavours...early and late.
The early ones let you adjust the mixtire by turning t he nut underneath. Far too simple and clever so it had to be changed.
Enter the later type which is a slotted tubed dog thingy, to stop the piston rotating and tearing the diaphram, and a long alen key that goes down the tube in the dog. You stick the tool down the bit where the damper goes, wiggle it til it engages on the piston and then try and engage the alen key in the jet /needle screw. You then turn the alen key to move the needle up and down.

Utterly horrible and well worth the weigh in ally value are these later 'bergs. You can get a single SU off a dolly 1300 that will work a whole lot better. There are also several other holes and tubes and bimetal strips and o rings that can stuff you up as well. Many a stag or early 'mite runs like a camel because of them.

Of course others will disagree...but those that know, know I'm right.

Jonners

[sprint95m]

Sorry for the earlier post, I had incorrectly thought that a Herald 13/60 would have a carb of the same design of an early
2000 mark 2 (CD150SEV). Those carbs with external jet adjustment were only available for a relatively short time on the
2000 mark one which predate the 13/60 I think.

Anyway, I have checked the SU Carb. Company's web catalogue and the good news is that the Stromberg you propose to use, Steve,
is the simpler design without the potentially troublesome temperature compensator (SEV), so Jon's sarcasm is misplaced in this instance .
I note that some discerning folk including Talbot, Volvo and Saab were using Strombergs well into the 80s.

[VYO 372M]

Sorry for the earlier post, I had incorrectly thought that a Herald 13/60 would have a carb of the same design of an early
2000 mark 2 (CD150SEV).

No problem Ian.

Thanks for the advice, it is a reconditioned carb bought from Canley Classics, so it should be ok.



The main reason I decided to go for a Stromberg 150 CD is because you can get a herald 1200 manifold adapter which bolted straight onto the cars existing manifold saving me having to change the manifold as well. I've had a couple of Herald 13/60s which have the early Stromberg 150 CD carb fitted and have never ever had a problem with them, hence my choice of carb for my 1200.

Steve