design - Land Rover section

 

Land Rover FAQs

 

QUESTION - There are several kinds of Rochester single barrel carburetors. How do I know which one to pick?

REPLY - The best is a Rochester B series from a 1952 or '53 Chevy truck equipped with a 216 Cu In 6 cylinder engine or a model 228 Zenith which is a modern update of the old Zenith 28 carburator.  Both the Rochester B series and the Zenith 28 were used on early Chevy six cylinder engines.

The Rochester:

Here's some carb numbers:

 

7004600

1949-1953 Chevrolet trucks with 216ci engine

 

7002051

1950  cheverolet trucks with 235ci engine
manual choke

 

7004468

1950-1951 cheverolet trucks with 235ci engine
manual choke

 

7004468

1953-1957 with 236ci engine

 

7007181

1950-1951 cheverolet cars with 235ci engine
Automatic choke

 

7003863
7003864
7002051

1951 with 236 ci engine

 

7004476

1952 with 236ci engine

 

7005140

1954 - 1956 with 261ci engine

 

NOTE: These are not all the numbers

Rochester B series
Rochester B Series carburetor

The Rochester B series carburetor originally came as a tall version designed to have the air filter clamped to the top of the carb.  The Land Rover 'L' shaped tube clamps nicely to this design.  Starting in 1957 the B series was redesigned incorporate a new low air horn design, to facilitate lower hood styling.  The stock Land Rover  tubing from the air filter will not fit this carb. 

The B series were manual choke and were standard fitment in Chevy trucks.  The BC series is the same carb but equipped with a automatic choke and came as standard fitment to Chevy pas sanger cars.

The Rochester B series carburetor with long neck came on three sizes of GM six cylinder engines, the 216, 235 and 261.  Each size engine used a different B series carburetor with a different size venturi.   The 216 engine is closest in size to the Land Rover four cylinder engine and has the smallest venturi diameter.  Larger venturi carbs work less well in the off idle and mid RPM range.

As near as I can tell the 216 was used on chevy trucks up to 1953.  The 235 was available on Chevy trucks 1950 through 1953 (maybe longer)  and the 261 1954 to at least 1957.  I'm limited by the issue date of the Rochester documents I examined.

You will need to reduce the size of the main jet.  50 or 52 is a good starting point if you are near sea lvel or 48, 49 if you are above 5000 feet altitude. The best way to pick a main jet is to put the car on an exhaust analyzer.

The Rochester is a simple, easy to rebuild, relatively inexpensive carburetor that provides an increase in fuel flow over the Zenith or Solex carbs. With a low restriction air filter, you should notice a slight HP increase on the open highway. This will be most noticeable on hills. Properly jetted, you should see very little fuel mileage loss if any. In my 109 I was getting an average of 16 MPG on the open highway (50-55 MPH). The float valve placement allows this car to work well under off road off camber situations. The main jet is mounted in the top cover making it immune to stirring up an sediment in the float chamber.  That is a problem with Webers.

Fitting the Rochester:

The series B Rochester is almost a direct fit to a Solex equipped LR engine.  The Zenith is turned 90 degrees to the Solex so the base adaptor will need to be removed and you will need to fiddle with the linkage. You will need to elongate the mounting holes at the base of the carburetor a little for a proper fit.

The early Rochester B series carburetor has a hole in the base.  This is the direct manifold vacuum passage which operates the sustained power system. This system provides additional fuel for sustained high speed operation or increased road load power It also helps with fuel economy. The bottom line here is that you do not want to cover this hole with a gasket.

Rochester base gaskets have a cut out slot going between this hole and the throat of the carb at the base. The Land Rover carb base gasket does not. Use the Rochester base gasket, NOT the LR carb base gasket.

Most auto parts stores carry a thick fiber spacer that fits between the Rochester carburetor and the intake manifold. This spacer helps keep the carburetor from getting too hot and vapour locking. It also provides an air passage between the hole in the base and the throat of the carburetor. Use this fiber spacer instead of the Land Rover spacer.

If you can not find the fiber spacer you can use three Rochester carb base gaskets stacked together on top of the Land Rover spacer to provide insulation and space for the vacuum flow.

I mounted a little nylon cable clamp to one of the screws securing the top plate of the carb. This cable clamp holds the choke cable housing in place.

From experience I have found that metal vacuum tubing between the carb and distributor vibrates and breaks when you drive wash board surfaces. I switched to a rubber tube vacuum line to solve this problem.

The carb is set up for a threaded tubing vacuum advance line. I ended up running about an inch of copper tubing from the carb, compressing a compression ring near the far end then running the vacuum tube over the compression ring & copper tube to the base of the carb. It seems to seal the vacuum effectively.

The stock air cleaner does not flow enough air for the Rochester to reach its maximum HP potential. If you wish to see extra HP from the Rochester you will need an air cleaner with a higher flow rate such as a K&N, or aftermarket filter with a paper element. However the K&N does not filter well enough for sustained use in a high dust environment and paper filters become clogged quickly under those conditions.

I recommend a high flow paper element filter or K&N be used for pavement driving and that you switch back to the stock oil bath air cleaner when driving off the pavement If you leave the stock filter in place it doesn't take long to make the switch and your engine will stay healthy longer.

Fittings on most if not all versions are 1/8" NPT.

Maintenance

Carb rebuild kits are inexpensive and readily available at almost every auto parts store. Carburetor specialty stores generally have a selection of main jets for this carburetor.

There is a pressure valve inside the carburetor body that consists of a steel ball and a spring. There is a metal rod across the top of the opening to keep the parts in place. A rebuild kit comes with a new ball and spring. Be advised that the spring rate is different than the original and replacing it can cause problems. Leave this pressure valve alone if you can when rebuilding the carburetor If you need to open up the passage reuse the old spring.

Float level (base of carb top to bottom of float, carb top upside down) = 1-9/32" using Rochester float gauge M-250.  Bend float arms to adjust.

Float drop (base of carb to to bottom of float, carb top right side up) = 1-3/4" using Rochester gauge BT-93.  Bend float tab at float valve to adjust.

The original Rochester factory part numbers for the gasket kit is 7004085 and 7009311 for the repair kit.  A current rebuild part number is 7004363.

 

The old car manual project has the manual for the B series Rochesters used on the 216 engine

The service manual for early B series Rochesters is also on line.

 

Zenith 228:

The Zenith Model 228 is a modern version of the Zenith Model 28 carburetor which was used on GMC 6-cylinder truck motors from 1946 until 1962. These engines came with either the Rochester B series or the Zenith 28 carburator.  The Zenith Model 228 is a current production carburetor made in Bristol, Virginia.   The Model 228 has a manual choke, comes in four throttle bore sizes and features interchangeable venturi sleeves. For ease of tuning, Zenith offers a wide range of jet and power valve sizes. It comes with throttle levers and air filter adapter that allow it to cover most of the original one barrel carburetors.

The Zenith 228 has a 1/8th pipe thread inlet and the same base fitting as the Rochester B series above. 

Rochester and Zenith comparison

228 specifications from the Zenith web site

REBELRODZ MAGAZINE - December 2009 issue

 

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