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Pierburg 2B5 / 2B7 Carburettor Information

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Old Mar 17th, 2013, 13:54   #1
OldBlueVolvo
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Default Pierburg 2B5 / 2B7 Carburettor Information

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

Attached Images
File Type: jpg ApplicationTables.jpg (78.3 KB, 42 views)
File Type: jpg carb specs.jpg (253.5 KB, 42 views)
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Old Mar 17th, 2013, 14:07   #2
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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.

Attached Images
File Type: jpg ChokeSleeve.JPG (66.6 KB, 41 views)
File Type: jpg AssembleChokeCam1.JPG (50.0 KB, 41 views)
File Type: jpg AssembleChokeCam2.JPG (49.0 KB, 41 views)
File Type: jpg AssembleChokeCam3.JPG (53.6 KB, 41 views)
File Type: jpg 2ndThrottlePlay.JPG (99.9 KB, 41 views)
File Type: jpg Throttle Body Gaskets.JPG (38.3 KB, 41 views)
File Type: jpg Throttle Body Screw.JPG (63.4 KB, 41 views)
File Type: jpg FastIdleGapFront.JPG (66.3 KB, 41 views)
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Old Mar 17th, 2013, 14:15   #3
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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.
Attached Images
File Type: jpg ReassemblePumpInjector.JPG (27.7 KB, 41 views)
File Type: jpg MeasureFloatHeights.JPG (51.8 KB, 41 views)
File Type: jpg FullLoadNozzleGap.JPG (72.5 KB, 42 views)
File Type: jpg SetDechoke1.JPG (50.4 KB, 42 views)
File Type: jpg ClearanceA.JPG (67.4 KB, 41 views)
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Old Mar 17th, 2013, 14:27   #4
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Float Chamber Gasket Template (not to scale)

  • Volvo p/n: 237957
  • Material: Abil Gb, made by Elring
  • Thickness: 0.8mm
See photo attached.
Attached Images
File Type: jpg Float chamber gasket - monochrome3.jpg (51.1 KB, 3 views)
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Old Mar 17th, 2013, 14:49   #5
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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.
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Old Mar 24th, 2013, 07:46   #6
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Default Pierburg choke system

Dear Mr. OldBlueVolvo,

My name is Imre Budahazi and I write to you from Hungary. My english isn't perfect, sorry about this. I bought a Volvo 740GL saloon last summer, and I have some problems with the car's Pierburg 2b5 (or 2b7?) carb. The car has very good condition. The first owner was the government and the biger part of the life of the car was spent there. After the driver gone to retire bought this car from the bureau. When he pass away, the car was waiting for new life and new driver under a tent for 2 years. This is when my story starts.

After the buying the car had some contact problems and ignition failure, therefore I changed the complete ingnition system. After I had been sucked for a long time with the hot start valve. The pipes were holey, and the car was stopped after every 10 kilometers, with indication of run out of gas, but the tank was fullfilled. I couldn't recognise the problem, because I didn't know what is the hot start valve. I used cars with carb since 10 years, but that cars has more simply carbs (like weber or solex). Then I get the black Haynes book, and I throw this valve away. The Volvo was never stop again.

Then come the winter and the Volvo give me new indicates. It won't like to start at the mornings. I had to push many times the throttle pedal, turn the ignition key for approximately 1 minute to start the engine, and hold the throttle pedal as long as the water gonna be hot. I disassemble the carb, and I see the complette choke system has a big failure. The vacuum unit is broke, the choke rod is lost, and the upper connection of the rod is also broke.

I ordered the new rod at the Hungarian Volvo HQ, but it still not arrived. I think it never will.
I buy a new vacuum unit at the ebay, but it's a part of the Pierburg 2b4 (for BMW). I hope it will be ok for my 2b5. My problem is, I can't order or buy the choke parts anywhere in the world, and i can't fix my carb.

My question is, where can I buy the parts? I saw you are very experienced about this carbs renewing and repairing method. I would like to ask your help, please. If you have these parts for sale, I would like to buy. I can pay it via paypal or bank transfer. Or if you can recommend a kind of shop I will very thankful!

I wait your answer!

Best regards,
Imre Budahazi (Bonecrusher)
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Old Mar 24th, 2013, 13:02   #7
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Mine's got a manual choke Weber now - it works.
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Old Mar 24th, 2013, 18:50   #8
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Quote:
Originally Posted by Volvorama View Post
Mine's got a manual choke Weber now - it works.
I think this is a good idea to change the Pierburg to a Weber. Where did you buy the adapter for the intake manifold?
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Old Mar 24th, 2013, 19:24   #9
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Hi bonecrusher, I would agree that replacing the carb with a new one would probably give the best results. I provided the info in this thread mostly for those who would like to keep their cars totally original but also for historical interest. If you are interested in the weber carbs then you can buy a kit for about £250+VAT here: http://www.webcon.co.uk/shop/shopdis...=411&cat=Volvo

There is one listed for with and without EGR. The kit includes the manifold adapter. The choke pull isn't very good so I have used a turn-to-lock choke in the past.
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Old Mar 24th, 2013, 20:17   #10
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Thanks for the useful reply and the shop address! I wouldn't like to spam your topic, but one little thing left. I think if I buy a brand new carb to my car I prefer the auto-choke system. Have you got experience with this kit with the electronic auto-choke?
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