PETROL FILTERS

I read with some interest the report on the Coast to Coast Run by Keith Sherwin in the August edition, in particular the bit about main jet blockage. I too had this problem last year, having put WW 1591 back on the road after 30 years in hibernation. Even after thoroughly washing the tank out, it would only run about 5 miles before spluttering to a halt with one jet or the other blocked with rust particles from the tank. Investigation revealed the filter in the bottom of the carburettor (bronze 22FZ,) to be full of evil looking brown gunge and the copper gauze itself was disintergrating, allowing all manner of junk to pass through.

Since we were leaving for Gaydon 97 rally next morning, a solution was required FAST. A new filter was needed. An in line filter was considered and rejected because:

I. It is non-original and such a modern appendage it looks quite wrong under an Austin Seven bonnet.

2. It costs money.

3. The shops were shut.

At this moment Norma walks into the garage with a cup of coffee and I show her the problem. "Well, I've just made this coffee using a filter, could this be made to fit." Possibly - I have to think about this. Just then my eyes glanced upon an SU petrol pump on the shelf and it occurred to me that they used a tubular filter very similar to the Zenith. Removal of the SU filter showed this was indeed the case. Early SU filters were copper gauze, but this was a more modern one made as a one piece moulding in some sort of plastic, very slightly longer and smaller in diameter than the Zenith. It was also a bit coarse. The holes in the mesh being bigger than the hole in an Austin Seven idling jet.

The original filter was dismantled by unsoldering. A useful tip here is to heat the filter to melt the solder, then drop it onto the garage floor when the shock breaks the solder into tiny globules and the components fall apart cleanly. The length of the SU plastic filter was reduced to the same as the copper gauze from the Zenith "original" by careful grinding (keeping the ends square), but it could easily be done with scissors. A coffee filter paper was then cut to produce a rectangle .2" X 4" and rolled up into a tube which was inserted into the shortened SU filter. Rotation of the SU filter against the wrap of the paper produced a tight coil ofjust three turns, with 3/16" sticking out of each end. This bit sticking out was now cut into 1/8" strips to make a fringe at each end of the filter. The fringe was bent back against the outside which increased the outside diameter just enough to allow the original Zenith end caps to be a tight push fit over the new filter. Reassembly of the curburettor with this new paper filter proved easy.

Experience to date with this mod over 3,000 miles has proved most satisfactory with no further jet blockages to date. The filter, however, has become choked with debris occasionally. This is easily dealt with in under five minutes by changing the paper, a stock of which, cut to size, is now part of the tool kit.