Pierburg 2B5 / 2B7 Carburettor Information

[OldBlueVolvo]

I started writing a manual for the Pierburg 2B5 / 2B7 carburettor a few years ago but didn't get very far with it. I'm not going to do any more work on it so I'll post up the photos and details I collected at the time. Hopefully someone else will take the baton and finish it? Feel free to post any info/photos/whatever related to this carb in this thread. It is quite possible that there are some errors that need correcting, so please post any corrections.


1 Vehicle Applications

The Pierburg 2B5 carburettor was fitted to the 740 models that had the B230K engine, during the 1985 and 1986 model years. Note that Volvo model years run from October to September. For example, the 1986 model year ran from October 1985 to September 1986. The Pierburg 2B7 carburettor was fitted to the 740 models that had the B230K engine between 1987 and 1990. The B230K engine in this period was known as the 'heron' engine and may sometimes be referred to as a B230KH to differentiate it from the earlier B230K engines. For completeness, a full list of the carburettors fitted to the 740 model is tabulated below. The Swiss variant of the 2B5 had different jet sizes to the 2B5 used elsewhere. Also the 2B7 had slightly different jetting to the 2B5 variants. Some of the differences between the 2B5 and 2B7 are that the 2B5 had a fuel return connection whereas the 2B7 did not. Also, the 2B5 utilised a 2-stage choke pull-down diaphragm whereas the 2B7 utilised a 3-stage choke pull-down diaphragm.




The above tables show the carburetted 740 models. There was also a carburetted version of the 760; the B28A. It used a single SU carburettor (volvo pn: 1269717).

2 Carburettor Specifications

[OldBlueVolvo]

6 Carburettor Reassembly

Once all of the components have been cleaned and checked for damage and wear, the carburettor can be reassembled.

If the choke assembly was dismantled then begin by reassembling it. Slide on the metal sleeve as illustrated below.



Assemble the fast-idle cam, spring, and bushing.



Put the fast-idle cam assembly on the metal sleeve and insert the choke shaft. This operation is a little tricky as the little plastic crank must be fitted to the choke shaft at the same time.



Attach the choke carrier with the three slotted cheese-head screws and ensure that the spring is fitted correctly.



With both throttle levers in their rest position (idle position), measure clearance Z on the secondary throttle plastic lever. It should be between 0.1-0.5mm. If it is out of specification it might indicate that the plastic lever is worn where it rubs against the primary throttle metal lever. Wear in this area can be filled with a suitable filler. After making any repair on the plastic lever, remember to check clearance Z again. In order to correct the clearance, bend back the metal forks.

Pull the plastic secondary throttle lever clockwise (releasing the lever should cause it to return by action of its return spring). Now measure clearance Y. It should be between 0.15-0.85mm. Correct clearance if necessary.



Make a sandwich of gaskets, in the order gasket-insulator-gasket, and place it between the main body and the throttle body. Fix the two bodies together using the single screw underneath the throttle body.





Open the primary throttle and rotate the choke lever until the fast-idle screw butts against the sixth step of the fast-idle cam. Measure the clearance between the primary throttle lever and its idle stop screw. This clearance is called the 'fast idle gap'. Note: Do not adjust the idle stop screw to modify this clearance. If the clearance is not within specification, adjust the fast-idle screw.

[OldBlueVolvo]

Reassemble the pump injector if necessary. Renew the small o-ring.



Push the pump injector into the main body.

Push the accelerator pump assembly into the main body so that the plastic bearing is flush with the mating surface. If the spring pushes the plastic bearing out then renew the bearing.

Fit new needle valves to the upper body. Check that the new needle valves are free to move up and down without any resistance. Refit the plastic floats using new pins.

Check for side to side play in the floats. Renew the float if the play is excessive.

Measure the float heights.



Screw in the two main jets.

Place the new float chamber gasket on top of the main body and carefully lower the upper body onto it. Screw in the four upper body screws/fasteners. Don’t forget to fit the ID tag to one of the screws.

On 2B5 carburettors without EGR, blank off the vacuum port to the left of the idle mixture screw using a rubber nipple cap.

Renew the o-rings for the idle speed and mixture screws and screw them in until they just seat. Then back them out a few turns. The correct size of o-ring is critical.

Screw in the three jet / air correctors at the top of the carburettor.

Check/set the distance between the full load enrichment nozzle and the choke flap to 0.5mm +/-0.75mm.



Fit the choke link rod.

Check/set the dechoke. To do this, begin by wrapping an elastic band around the choke lever and upper body to close the choke flap, as illustrated below. Now fully rotate the primary throttle lever to open the throttle. One should see that the choke flap is forced open slighly at wide-open-throttle. Measure the choke-flap opening with a drill shank. It should be 5.7 +/-0.5mm. A 6mm drill would suffice if a 5.7mm drill is not available. To adjust the clearance, loosen the primary throttle spindle nut and slide the de-choke cam up to increase the de-choke, or down to reduce it. Afterwards, tighten up the nut and re-check the clearance, then remove the rubber band.



Fit the choke diaphragm with its inlet hose and reducing jet but do not connect the other end of the hose to the base of the carburettor yet.

Open the throttle roughly half way to allow the fast idle screw to be placed on the seventh step of the cam, and release the throttle lever once that is done.

Measure the clearance (A) between the choke diaphragm plastic rod and the choke lever. It should be 0.75 +/-0.25mm. If necessary, adjust by bending the small end of the choke lever.



Check the setting of the choke diaphragm.

Connect the choke diaphragm inlet hose to the base of the carburettor.

Screw in the fuel cut-off valve.

Push the accelerator pump link rod back into its bushing on the throttle lever.

Refit the secondary throttle diaphragm.

Screw in the centre bolt at the top of the carburettor.

Attach the hot start valve.

[OldBlueVolvo]

Float Chamber Gasket Template (not to scale)

• Volvo p/n: 237957
• Material: Abil Gb, made by Elring
• Thickness: 0.8mm

See photo attached.

[FossilFish]

Thanks for the info and taking the time to post all the above, its all too technical for me but good to know that there are folks around who are clued up.

[cumbrianmale]

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