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Old 10-28-2011, 08:14 PM   #70 (permalink)
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Join Date: Jun 2011
Location: Essex UK
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Update 008
This update covers one of my biggest hurdles in the frame construction process, the relocation of the carburettor to fit within the engine compartment. I’ve chosen to show the stages of fabrication before completion to illustrate the challenge and possible solutions.

Here is how the engine currently fits in relation to the seat and frame. The carb must fit below the frame bars and allow for a filter to be fitted. The incoming (cold) air comes from below the footbox section and the intake port is located on the top of the cylinder head.

The new port will be constructed from TIG welded sections of aluminium and a short section of original casting.

I’ve already made my “tube” by turning out the centre of some suitable aluminium bar stock, and then cutting short angled sections with which to “lobster back” the gentle curves between carb and head.

So the goal is to fabricate a new inlet port, locating the carburettor low down, facing forward into the incoming airflow. This is necessary to keep the carb position away from the drivers legs and outside the compartment for noise and safety reasons.

There are some obvious problems with this solution – the longer tract length and the vertical distance. The inlet tract will be approximately 200mm longer than original. This will have an effect upon throttle response and the engine torque curve, but I hope that the effects will not be severe. The vertical section should also have a negative effect, but its not clear how large this will be, mainly because this type of system is rarely employed. The effect on driveability will probably be masked by all the other changes to the vehicle making it difficult to evaluate. These problems are temporary in any event, eventually the system will be redesigned to allow fuel injection as part of the “stage two” power upgrade.
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