Don’t break the bank balance with throttle bodies. We’ve found the cheapest solution to performance fuelling — here’s how to fit bike carbs to your classic Ford
There was a time when a fuelling system was cheaper than a second-hand engine. Nowadays, a new pair of 40 mm carbs and an inlet manifold can almost be as expensive as a set of throttle bodies or an aftermarket fuel-injection system.
One alternative solution is to fit a set of motorbike carburettors. This is a popular solution for inline four cylinder engines with four inlet ports in the cylinder head. A set of four carburettors from a Honda Fireblade, Blackbird, Kawasaki ZX, Suzuki Bandit or Yahama R1 for instance, can be fitted using a suitable inlet manifold, which is manufactured by a number of specialists including DanST Engineering.
Budget for under £200 for a suitable inlet manifold, £100-£150 for a set of carburettors and another £100-£200 for an air filter, manifold gasket, motorbike fuel pump and cables (choke and throttle).
So what are the benefits of four bike carbs? A more responsive throttle pedal, easier maintenance and straightforward cold starting with a manual choke are some of the answers. You won’t get more performance over a pair of Webers, but they are often cheaper, just as reliable, more fuel efficient and easier to set up.
The following pages cover stripping down and modifying Yahama R1 carburettors and fitting a set of motorbike carbs to an engine. The information acts as a general guide, so it’s worthwhile speaking to the specialists we’ve mentioned for specific advice and parts on your own Ford. Set aside a weekend to complete all of the work shown.
Buying bike carbs
A set of motorbike carbs should cost between £100 and £150 from motorbike breakers. Try to buy the backing plate for the air filter box, because it can be used as a template to make your own air filter. When buying second-hand, look for accident damage. Check the throttle and choke linkage operates freely and the butterflies close together (the spindle may be bent if they don’t close together). Ensure the plastic diaphragm covers are not cracked because a cracked cover will affect the operation of the diaphragm and needle inside, causing uneven fuelling.
How to fit bike carbs
With the old carburettor(s) or fuel injection system removed (including the inlet manifold), fit the new manifold with a new gasket or in some cases, a bead of sealant.
Most bike carbs are secured to the inlet manifold with fluoro-lined silicone hoses (the lining is suitable for petrol). These can be fitted onto the carburettors first and retained with narrow band hose clips.
The carbs and hoses from the last step can now be manoeuvred into position and fitted onto the inlet manifold. Secure them with more narrow band clips. Jubilee clips are not suitable as they will foul the throttle linkage.
Connect the choke and throttle cables, the throttle position sensor (if fitted) and fit an air filter.
Throttle and choke cables
Use a bicycle brake cable for the throttle cable. Ensure it has a solderless nipple to connect to the accelerator foot pedal. If the throttle cable fouls the underside of the bonnet where it’s connected to the carbs because the angle of the connection points upwards, fit a 90-degree throttle linkage connection from the R1, which can be sourced from a motorbike breakers yards or a Yamaha dealer. A manual choke cable needs to be fitted, which can be operated from inside the car. Use an old choke cable and sleeving.
Fuel pumps and regulators
The fuel pump that accompanies the motorbike carbs is often worth using. For instance, the Yamaha R1’s electronic fuel pump contains an interrupter pump to stop the fuel supply when the carbs are full, so you don’t need a fuel pressure regulator. If you want to fit a new fuel pump, a cheap solution is a Facet pump and Filter King pressure regulator. Check the maximum fuel pressure for the carbs -— the R1 is 3 psi. You will also need to fit an inline filter between the petrol tank and fuel pump and use 8 mm fuel lines throughout.
Words and Photos Rob Hawkins
For the full lowdown on how to buy and fit bike carbs, check out the March 2017 issue
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