Comparing Pattern Parts with Old Genuine Ones

Just over a year ago, I fitted new inlet rubbers to my Kawasaki Z650. They were pattern ones, but bought from a reputable dealer and supposedly high quality.

A year later, the bike just doesn't want to start. When I drained the carburettor float bowls, there was quite a lot of fine debris in the petrol that came out, which I identified as being due to the fuel hose being partly perished.

Then I saw the state of the inlet rubbers, a year after I fitted them and with the bike still being an ongoing restoration project not yet fully on the road. I was shocked !

Luckily when I sorted through and catalogued my backlog of spare parts, I found a set of rubbers I'd forgotten I had. After about 15 years of sitting in a shed in their original packaging, they are still soft and flexible. The contrast between these NOS (New Old Stock) and the more recently made pattern parts is incredbile.

All photos by me

When I flex the pattern ones, their failure is even more obvious.

Although I can't feel the damage going through to the inside, I'm fully expect that they'll be leaking air.

I'm not a scientist, but I have a strong suspicion that the ethanol in modern petrol (I use E5, but it's still 5% ethanol) is responsible for destroying rubber it comes into contact with. I've now managed to get some lead replacement fuel stabiliser, so I really hope that helps preserve rubber parts.

The conclusion is clear; genuine Kawasaki parts, even very old ones, are better than modern copies as long as they are stored correctly. I might buy one or two new genuine ones to see whether their current standard of manufacture is as good as their original standard.