Technical Articles

Harley Carburetor Overhaul Kits

JAMES GASKETS manufacture all the gaskets and seals required to service the Linkert, Bendix and Keihin carburetors fitted as original equipment to Harley-Davidson motorcycles from 1936 through to 2006 when the carburetors were finally phased out.

We have chosen a carburetor from either end of this 60-plus year spectrum which we will completely overhaul using the James gasket kit for the specific carb selected. Any hardware required to bring this carb back to as-new condition will be selected from the Colony inventory held at Redgrave Motorcycles.

A Linkert was chosen as a good all-round example of the early carburetors. Linkerts were fitted to all H-D 80”, 74”, 61” and 45” engines up until 1965. The earliest application for these carburetors appears to around 1930; up until then Harley was using Schebler carburetors which were very similar to the early Linkerts. We will concentrate on the Linkerts produced from 1936 onwards and in particular the M74B fitted to FLs and FLHs from late 1951 until 1965.

The carburetor is the plain tube type with a venturi and a discharge nozzle which draws fuel from the float bowl. This is metered by two jets, one for low speed and one for high speed.

The extreme simplicity of the Linkert is obvious in this exploded view of a typical Linkert.

These are all the pieces supplied in the various James Gaskets carburetor kits. The gaskets and seals are of the very best quality and are suitable for today’s fuel.

New needle and seat with correct washer ready to be installed. The thickness of the washer used to seal the seat against the floatbowl is very critical as it affects the height of the seat in relation to the rim of the float bowl.

The fuel filter will have a new Colony strainer added to complete this section of the carb.

If necessary complete fuel filters are available from Colony and stocked by Redgrave Motorcycles in three versions for accurate restorations of the various year groups.

The new float bowl gasket in place. At this stage the carb is going back together after being completely dismantled and cleaned. Throttle shaft bushings have been replaced and sized.

With the venturi, main nozzle and retaining spring back in place, and float correctly adjusted, the float bowl can be installed with the new copper washer furnished with the James kit and a new Colony float bowl nut.

If the venturi is damaged or there is some doubt as to whether it is the correct venturi for your project carburetor, Redgrave Motorcycles has a full range of new venturis for all popular Linkerts.

Generally the float bowls will need to be left slightly loose to gain optimum alignment with the fuel line after the carb is tightened up to the inlet manifold, The float bowl nut can then be snugged up. This particular model has two small dowels that locate the needle and seat section of the bowl in the centre of the carb body. The fuel filter will need to lined up with the rigid fuel pipe before it can be tightened for keeps.

The completed carby ready to be installed with some Colony hardware.

Starting in 1948 Harley-Davidson furnished an insulator block with the Linkert carbs. This is the reason for the second four-bolt manifold gasket supplied in the kit, one either side of the block. The inclusion of the insulator block and the second gasket meant longer screws were required. These hex-headed screws come with a slot as well and can be run up with a screwdriver then tightened with a 7/16” socket. These special screws are available from Colony.

Correct air cleaner screws and a fresh set of lock-plates are another Colony specialty and will be used to hold the original air cleaner in place.

First fitted in 1990, the CV carbs are the last style of carburetor to be fitted to Harley-Davidson motorcycles. These are a particularly good carburetor and are much sort after by owners of earlier models.

The CV carburetor is a constant velocity style with gravity feed and a float operated inlet valve and features a variable venturi. Rather than a choke like the Linkert, the CV has a fuel enrichment circuit for starting

After washing and inspecting, the carburetor can be reassembled with the components from the James Gaskets #27006-88 carburetor kit.

The new needle, which comes in the kit, can be dropped into position and the float can be slipped into place and accurately adjusted.

Adjusting the float level. With the carburetor body held at an angle between 15 and 20 degrees to a horizontal surface, the setting should be 0.413”—0.453” from the float top the float bowl surface.

Diagram : Page 4-17 ‘91 and ’92 Softail service manual.

Exploded view of the CV carby.

The float bowl can now be installed as soon as the new moulded seal is pressed into its retaining groove.

A new diaphragm, spring and boot for the activating rod, as well as two small O-rings, are required for the accelerator pump.

The diaphragm for the vacuum piston is not included with the overhaul kit and if damaged must be bought Genuine. This one was in perfect condition and was simply cleaned and reinstalled with the piston/slide spring and needle assembly.

This completes the service of the Keihin CV carburetor, a very straight forward procedure with no machining required, just a thorough cleaning, some minor adjustments and careful assembly using the quality components from the James Gaskets kit.

If you’d like more info on James or Colony products, call Richard at Redgrave Motorcycles: 02-9484-9900.

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