The early models have three outputs from the fuel tap to each carburetor. The later models have one output to a rack mounted manifoil distributing the fuel to the carbs.

There are three fuel filters. One for the main tank and one for the reserve tank. The last one is in the bottom and can easily be maintained and cleaned.

How to test the function:

The valve in the tap is vacuum driven. Here is a simple test setup to verify its function:

I’m using a syringe to make the vacuum for opening the valve. I let the denatured alcohol stay in the upper syringe over night to be sure there were no leakage at the ON postion. When moving the lower syringe the vacuume open the valve and it all works fine. Please watch the video:

If the fuel tap is not working you can strip it down, clean and replace parts (if you can find a new part).

I swapped some parts from the later model, but most parts are different. I was only able to swap the bottom filter + the gasket.

The bottom filter:

Looks like the filters are the same on all models.

Petrol tap switch:

The gasket behind the cover is different on J-K models compared to later models. Don’t waste money and buy the wrong one.

This is the correct type of gasket for the J-K model. The hole at the center is smaller on the early models + layout of the channels are a bit different too. You can’t swap the gaskets from later to old models.

If you have a leakage, the tension of this spring located under the cover can be the issue. If the movement of the arm feels to loose, bend the spring a bit to make a better tension to the gasket.

How it all works:

ON postion:

Main tank will flow to the vacuum valve (as the arrow on the picture in the middle show)

RES postion:

The RES will flow to the vacuum valve.

PRI postion:

The RES will flow to the PRI (direct to the carbs bypassing the vacuum valve)

Vacuum valve:

If you open the vacuum valve, be sure to assemble correct. The hole in the diaphragm have to fit to the gasket and hole shown in the picture above.

Replace the o-ring in the valve if needed.