Thread: How to set mixture on Stromberg carbs?

Some time back I scanned this book on tuning Stromberg CD carbs and have posted it on my website:

http://p38arover.com/misc_files/Tuni...CD%20Carbs.pdf

Thanks for that, p38arover. Those notes are for the older type carby with the bottom jet adjustment screw (like the ones i removed). The tuning process sounds similar, but i still can't quite picture the method of lifting the air valve 0.8mm. Those notes mentioned something about a piece of wire... Anyone done this?

You lift the piston - when I had stromergs they were fitted with a pin that could be accessed from the side and you could lift the piston with your finger.

If the later units don't have this pin I guess you could use some stiff wire (like welding wire) to lift the piston, with the air cleaner branches removed - may need to pull the dampers before hand.

You just get a small screwdriver and stick it in from the mouth of the carby.
Revs rise while up OK
Revs drop or stall too lean.
Turn needle adjuster to adjust (BTW its the weight of the adjuster that upsets the mixture while adjusting so you check before and after not while doing it, and also try a nd support the weight with your hand)
Rev and hold at 2500 or so for a short time and let settle between adjustments.
Regards Philip A

Thanks, PhilipA

Thats what i needed. I was thinking about accessing the piston from above, down the hole. Completely missed the fact that the piston is visable when the intake is open (i've got LPG, so it looks a bit different).

Thanks guys

All the info here is good. A couple of things though - I had twin Strombergs in a Volvo years ago, and found that the mixture needed to be leaned out to the point that there was barely detectable rise of revs, when lifting either of the pistons at idle. (I checked this with a Colourtune sparkplug! There's a blast from the past!).

I don't know about LR Strombergs, but on my 1972 Volvo, there was no mixture adjustment nut on the bottom of the carby. One needed 3 little tools to move the jet, which was an interference fit in the carby body. There were 2 screwable press things, one for the top and one for the bottom, and a spacer to go in the carby intake between the jet and the piston. This allowed purchase on the top of the jet assembly to raise or lower the jet to adjust the mixture, using either the top or bottom tool. I may still have these somewhere, I think. My Volvo was running very rich, so that it stalled in heavy traffic on hot days, and the dealers didn't seem to be able to get it right. I therefore purchased the tools myself - end of problem!

These "semi-adjustable" carbies came in with the first of the emission controls in the late 60's early 70's in Europe & US.

Cheers,

Lionel

Well, i balanced the carbies using the hose-in-intake-and-ear method and was suprised how easy it was to set

Lifted the pistons a little and no change. Lifted then a lot (4mm) and the revs dropped slightly. All this with no mixture adjustments

As mentioned, i set the needles so they were level with the bottom of the piston (that is, the little washer is level, not the bottom of the needle base). Could it be that this has provided me with the exact mixture setting? Or have i done something wrong?

PS: The car really goes now, sounds better and idles better - just from balancing the carbys

Originally Posted by Bulldog

Well, i balanced the carbies using the hose-in-intake-and-ear method and was suprised how easy it was to set

Lifted the pistons a little and no change. Lifted then a lot (4mm) and the revs dropped slightly. All this with no mixture adjustments

As mentioned, i set the needles so they were level with the bottom of the piston (that is, the little washer is level, not the bottom of the needle base). Could it be that this has provided me with the exact mixture setting? Or have i done something wrong?

PS: The car really goes now, sounds better and idles better - just from balancing the carbys

I would say you've got it spot on! You are lucky that you have not had to move the jets themselves.

The hose idea is not bad for the idle adjustment, and if it's running well, then leave it.

Cheers,

Lionel