How to overhaul a Stromberg carburettor

Here you can get How to overhaul a Stromberg carburettor, Removing the dashpot and piston, Adjusting the float and Stromberg CD3 ect.

The Stromberg carburettor doesn’t have a daily service schedule, but should be cleaned about once a year. Replace worn parts as necessary. Dirt which has penetrated the filter , and residues from chemicals in petrol build up inside. Needles and jets wear out after a couple of years’ use. The rubber diaphragm may become holed – and even a small hole causes loss of engine power. because the hole enlarges, the engine will eventually do no quite idle.

Remove the carburettor from the car to wash it. Keep it upright to avoid spilling petrol, then empty it safely. Clean all parts except the diaphragm by rinsing during a dish of petrol.

Removing the dashpot and piston

Unscrew the damper from the highest of the piston chamber – commonly called the dashpot . Pour the oil inside it away. Mark the dashpot top in order that you’ll refit it to the chamber an equivalent way round. Remove the screws and take off the highest carefully, ensuring that the piston spring doesn’t catch then drag out the piston.

Check that the diaphragm, which can begin once you remove the piston, isn’t stuck down around its edge: it’s easily torn. Lift out the piston, pulling it straight up so as to not bend the needle in its base. Note that on the diaphragm edge there’s a tab that matches into a squeeze its seating on the chamber base.

After reassembly, refill the dashpot with multigrade engine oil to just above the level of the brass piston inside the tube – or you can obtain a special SAE 20 oil made by the carburettor manufacturers.

Replacing the jet needle and diaphragm

A badly worn jet needle features a groove round it, but less severe wear is invisible. Wear does, however, affect performance, so replace the needle every few years. There are many needle sizes: make certain to urge precisely the right one. Remove the needle by loosening the grub screw within the side of the piston.

To remove the diaphragm carefully undo the screws of its retaining ring. Lift off the retaining ring and diaphragm. Hold the diaphragm up to the sunshine and check it minutely for the tiniest hole. if it’s become perished, hard or misshapen, renew it.

Be sure to suit the new diaphragm the proper way round and therefore the right high . there’s a tab on its inner edge that matches into a recess within the piston. Take care to not get oil or petrol on the diaphragm, and to not nick or tear it. Loosen the grub screw to free the needle. The diaphragm is held on by a ring and four screws; do not nick the rubber with the screwdriver as you remove them. Pull the diaphragm gently and hold it up to the light to show any pinholes.

Dismantling the float chamber

Before removing the float chamber, pull the adjuster stop off the jet with pliers. Note that emission-control models (See Adjusting an emission-control carburettor ) don’t have such a stop. Take out the six screws securing the float chamber. you ought to then be ready to lift the chamber off — but the sealing ring round the jet may make it stick. Pull carefully: a pointy jerk or twist might damage the float. With the chamber removed, pull out the float pin to free the float.

Older models have a pin that you can usually remove with your fingers. If it is stiff, gently prise it out sideways with a thin screwdriver. Emission-control models have a pin set in clips: lever it out carefully with a screwdriver. The float needle valve is screwed into the base of the float chamber. It is in one piece and cannot be dismantled for cleaning. If it is worn it must be replaced. If the float needle valve is blocked you may have to replace it.

Adjusting the float

A float is maladjusted, or is leaking in order that it not floats properly, causes persistent flooding of the carburettor. Shake it – if fuel splashes inside, it’s leaking and must get replaced. If adjustment fails to cure the flooding, that too involves a replacement float and a replacement needle valve.

With the carburettor upside-down, measure the height of the bottom of the float (now at the top) above the edge of the body. The height should be 16 to 18mm long for a hollow float or 18.5 to 19.5 mm for a solid float.

Adjust the float by bending the tag that touches tho needle valve, or by fitting a thicker or thinner washer under the valve. With the carburettor inverted, measure the height of the float above the body edge. Bend the tag to adjust the float height.

Removing the jet

Do not remove the jet of an emission-control model (See Adjusting an emission-control carburettor ): a special adjusting tool is required for its castellated adjuster nut. don’t even turn it: this alters the mixture. Clean it in situ by washing with clean petrol; blow it clear with a foot pump .

Remove a standard jet by unscrewing the holder, employing a spanner on the lower of the 2 hexagonal parts. don’t move the jet-adjusting screw, as this may alter the mixture (See Adjusting a Stromberg carburettor ).

Lift off the jet holder and pull out the jet. Wash the jet in clean petrol and blow through it with a foot pump to clear it. Check the rubber ‘0’ ring round the jet holder for signs of wear or cracking. A failed ring will allow petrol to leak from the float chamber. Lever off the ring with a pin or thin screwdriver; take care not to scratch the surface. Roll the new ring on over the holder.

Adjusting a Stromberg CD3

The CD3 carburettor features a fixed jet, and therefore the needle is loosely mounted within the air valve, or piston, in order that it centres itself.

You need a special tool to reset the mixture, which is completed by altering the peak of the needle within the piston. The tool may be a long L-shaped hexagonal Allen key which matches inside a thick-walled tube. Its maker’s part number is B20379. To use the tool, remove the dashpot damper and insert the tube in its place. Turn the tube until a pin on its side falls into a squeeze the air-valve shaft.

Push the Allen key to the bottom of the shaft and fit it into the needle adjustment. Before you turn the Allen key, hold the outer tube of the tool firmly; otherwise the air valve can turn and tear the rubber diaphragm.

Tune the carburettor with the engine running at working temperature, within the same way like the CD and CDS. For this carburettor, turn the Allen key clockwise to lift the needle and thereby enrich the mixture and anticlockwise to lower the needle for a weaker mixture. Take care to not turn the adjustment too far, or the needle can come loose from the adjuster. The range is merely about two full turns.

If you discover you’ve got to form quite a small adjustment, avoid losing the needle. begin the duvet of the carburettor and scoop the air valve, holding it by its shaft so as to not damage the diaphragm. Then set the needle during a midway position with the Allen key. The right position is when counting on the needle fitted – the washer round the needle or the groove in it’s flush with rock bottom face of the air valve.

Reassemble the carburettor and adjust the needle – ranging from now – no quite one turn either way. After each adjustment is formed , run the engine at about 2,000 rpm for ten seconds approximately to clear the additional fuel which tends to urge into the manifold once you are making an adjustment.

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