Title: Stromberg 175 CD-2S Overhaul Author: Rob Created Date: 3/18/2015 7:49:19 PM Keywords. Re: idle mixture adjustment on the stromberg 175 cd-2 Post by MichaelDesna ยป Mon Aug 31, 2020 2:53 pm Thanks for that info, Mark, but I think that the problem may be something that John was talking about and I want to try to check the diaphragms first before changing the needles out, both of which I know nothing about at the moment.
Zenith-Stromberg carbs were original equipment on classic cars such as Jaguar, Saab, Volvo, and others. North American-bound Triumph and MG sports cars were also fitted with the Stromberg.
Carb ID
The size and type of Z-Stroms are given in numbers and letters. For instance, numbers CD125, CD150 and CD175 are sizes relating to the choke diameter (1-1/4', 1-1/2', and 1-3/4'). They all look very much alike, but details such as throttle linkage will change from car to car.
One style is the variable-venturi side draft carburetor. Inside the carburetor, there is a piston connected to a needle which slides inside the fuel jet. This is in contrast to the more common fixed-venturi carb, where varying air velocity in the venturi alters the fuel flow.
Constant-Depression (CD) Carburetor
The vacuum-operated piston has a long, tapered, conical metering rod. This rod fits inside an orifice, which allows fuel into the airstream as it passes through the carburetor. The movement of this piston controls the amount of fuel delivered, depending on engine demand. As the tapered needle rises and falls, it opens and closes the opening in the jet, which regulates the passage of fuel.
Leaking Carb
A carburetor gas leak generally starts after a car has been sitting for many months. Fuel sitting in the carburetor evaporates, causing the float to drop and the valve to open.
Another cause of gas leaks is the needle valve not closing when the chamber is full, which allows it to overflow. You'll want to check both the float chamber gasket and the O-ring around the sealing plug in the bottom of the chamber.
Jaguar XKE Carbs
The 1967-1975 Jaguar E-type with the 4.2 engine were factory-fitted with a pair of Zenith-Stromberg carbs. These were emission-calibrated to meet U.S. air-quality standards. The loss of horsepower was offset by having a cleaner-running engine. (Note: 1971-1975 Jaguar V12 engines used two pairs of Z-Stroms, which flanked both sides of the engine.)
Because this car had sat in storage for years, the gasoline in the carbs turned to varnish. First, the carbs were removed, all the while taking notes and pictures on how they reassemble.
Rebuilding A Zenith-Stromberg
No special tools are required to remove and disassemble the carbs, but there are special tools needed to tune them. A service manual is essential for Zenith-Stromberg rebuilding and tuning.
Once disassembled, the pieces were chemically cleaned.
Soak the Carburetor
If you need to rebuild a really old and dirty carburetor, invest in a gallon can of Berryman's Chem-Dip. This stuff will dissolve the old dried-up remnants of fuel and remove any sludge. Be careful though, it will also eat plastics, puff up gaskets, and remove paint.
Shop: Berryman Parts Cleaner with Basket
Once the chemicals were done dissolving the dirt and sludge, the fuel bowl was lightly scraped and cleaned. Air passages were blown clear with compressed air.
A little brushing from a nylon brush will help clean things up. Rinse the carburetor and parts with water and dry with compressed air.
After soaking it, you'll still need to run something through the small passages to clean out the stubborn junk. You'll be surprised at how much stuff comes out of the ports.
Shop: Carburetor Cleaner Brushes
More cleaning followed, and then the carb rebuild kit followed. New gaskets, diaphragms, seals and o-rings were installed. It's nice to have a second carburetor to use as a reference as you're disassembling the other, but keep in mind that front and rear carbs can be different from each other.
Replacing The O-Ring
There is a small star washer and screw that keep the assembly from coming out. Once the nut, washer and metering needle are removed, the piston is empty inside. Clean the inside and outside thoroughly. The new O-ring sits on the needle adjustment screw. The replacement O-ring may be made of Viton, which holds up better to oil than conventional rubber.
Diaphragm Alignment
Upon re-assembly, note that the piston has an alignment tab and groove. The inside rim of the diaphragm has the matching tab. Making sure you don't have it upside-down, line up the indents to correctly seat the diaphragm.
Oil The Carburetor
To prevent erratic and sudden movement, a small amount of oil sits in the carburetor dashpot to dampen the piston. If there is no oil in the dashpot, the engine may be difficult to start. The engine will probably not accelerate quickly, because there is no enriching during increased load (accelerator pump function). It may also cause a lean stumble and accelerated wear. Conventional engine oil can be used.
You cannot overfill a Zenith-Stromberg carburetor with oil.
Read: 1968 Jaguar XKE Restoration
Zenith-Stromberg 175 CD2 SE units were used on 1970 140 series models, and on. Read the instructions and study the exploded view of the carburetor. Screw and locknut on my Zenith Stromberg 175 CD-2 carburetors? Could wish to know about these carbs, a lot more than in the manual!
As far as I know the MGB always had the ZS with a float bowl plug, but I could be wrong. Have you tried any Triumph sites? TRs used many variations of the 175CD-2. If you need a replacement stock carb I've got a spare one. You just have to supply the heat mass for the auto choke. Eric Triplett 'Electronic ignition, the greatest thing that ever happened to carburetors.' 1968 High Compression Engine, Dual SU HIF-4 Conversion, Peco Header and Exhaust, Pertronix LU-147, MSD Blaster 2 Coil.
Advanced Distributors Re-Cruve 45DM.
A Stromberg carburettor The Stromberg CD carburettor, like the SU (See ), is a constant-depression carburettor, hence the CD. The two work in much the same way, but the Stromberg differs in having an air valve - commonly called the piston - surrounded by a rubber diaphragm in the dashpot.
The size and type of a Stromberg are given by numbers and letters. Numbers such as 125, 150 and 175 are sizes: they mean a choke diameter of 1 1/4, 1 1/2 and 1 3/4 in. The size makes no difference to the way you tune the carburettor.
Types include CD, CDS, CD2S and CD3, all used on older cars made before anti-pollution laws demanded emission-control fittings. Later types with emission control have the letter E, as in CDSE and CD2SE. Tuning methods vary according to type, but Strombergs are not stamped with their type marks. Information in the car handbook should help you to identify your type.
Air cleaners. Leave the air cleaner in place if you can, so that adjustments are made with the carburettor as close as possible to its normal working condition. However, this may not be possible, depending on the car, the type of carburettor and the adjustment being made. Before starting to tune the carburettor, check out all the other systems such as sparkplugs, contact-breaker gap and the ignition timing (See ). Although valve clearances seldom need resetting between major services, always check them before attempting to tune the carburettor. Check, too, that the damper tube is topped up with oil to within 1 in. (6 mm) of the end of the rod.
Use ordinary multigrade oil or the special SAE 20 oil made for the purpose by Zenith (the makers of Stromberg carburettors). Tune with the engine running at working temperature. Adjusting the gap Adjusting the gap The fast-idle stop screw opens the throttle when the choke is pulled out. There must be a gap between its head and the choke cam when the choke is pushed home.
The CD and CDS have different cold-starting devices, but the adjustment works in the same way. Set the gap according to the car-makers recommendations - usually about 1mm.
Some Strombergs have a two position screw to limit the use of the choke according to the season. It has a spring under its head. Set it with the spring compressed for summer and the tension released for winter (only necessary in freezing weather) Tuning the CD, CDS and CD2S. If there is no pin, lift the piston with a screwdriver. If there is no pin, take off the air filter and lift the piston 1/32 in.
(1 mm) with a thin screwdriver. Listen to the engine note while you do so. If the mixture is correct the engine speed should rise slightly for a moment, then return again to normal. If it rises and stays fast the mixture is too rich. If the engine dies when the pin is lifted, it is too weak.
Switch off the engine before adjusting the mixture, and check that the jet needle is central. Remove the air cleaner, lift the piston and let it fall. If the jet is central, the piston falls with a sharp click. Keep the jet central while you adjust the mixture by taking the damper rod out of the top of the carburettor and pushing a pencil or soft metal rod firmly down the hole to hold the jet in place. Make sure that the jet remains centralised. Use a coin to turn the jet-adjusting screw one-eighth of a turn at a time, waiting each time for the engine speed to settle down.
Screwing upwards weakens the mixture, downwards enriches it. Start the engine and bring it up to working temperature. The mixture-adjusting screw is set centrally in the base of the carburettor on CD, CDS and CD2S models. It is brass and has a wide slot in it.
Although a screwdriver can be used to turn it, a small coin is easier. Turn only an eighth of a turn at a time, then wait about 15 seconds for the engine speed to settle down. Lift the pin again and see whether the engine speed alters. Screw the jet upwards (that is, anti clockwise looking down on the carburettor) to weaken the mixture, or down (clockwise) to make it richer. With the mixture setting correct, the idling speed may now be too fast or slow.
For most cars it should be 850-950 rpm - judge it by ear if your car does not have a tachometer (or rev counter). Adjust the idling speed by turning the throttle-stop screw.
Stromberg Cd 175 Carburetor
If tuning fails to make the engine run properly, the carburettor may need cleaning (See ), or the air filter renewing. Centralising the jet.
Stromberg 175 Cd 2 Manual Pdf
Stromberg 175 Cd 2 Manual
Lift the piston while you adjust the height with a coin. Lift the piston so that the needle is clear of the jet, and screw the jet adjusting screw up until the top of the jet is just above the top of the bridge in the carburettor bone. Use a spanner to slacken the large nut just above the jet adjusting screw by half a turn.
That releases the jet in its housing, but allows it to drop slightly. Wind the jet adjuster up again until the top of the jet is level with the bridge. Let the piston fall back gently so that the needle centralises the jet. Remove the piston damper and hold the piston down with a pencil or soft metal rod slipped into the damper tube. Tighten the jet assembly.
Check several times that the piston drops with a click. The CD3 is a fixed-jet carburettor and you need a special tool to reset the mixture control, which is done by altering the height of the jet needle. The CD3 carburettor has a fixed jet, and the needle is loosely mounted in the air valve, or piston, so that it centres itself. You need a special tool to reset the mixture, which is done by altering the height of the needle in the piston. The tool is a long L-shaped hexagonal Allen key which goes 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.
Stromberg 175 Cd 2 Manual Transmission
Turn the tube until a pin on its side falls into a slot in the air-valve shaft. Use an Allen key to set the needle in a midway position. The right position is when depending on the needle fitted - the washer around the needle or the groove in it is flush with the bottom face of the air valve. Reassemble the carburettor and adjust the needle - starting from this point - no more than one turn either way. After each adjustment is made, run the engine at about 2,000 rpm for ten seconds or so to clear the extra fuel which tends to get into the inlet manifold when you are making an adjustment. If you do not have a revolution counter or tachometer, listen to the engine note. Its pitch should rise a little more than an octave above its normal sound when idling.