Q I’ve just replaced the head gasket on my 1991 City. When I had the head off I lapped in the valves and replaced the
seals as you do. Anyway couldn’t help but notice my exhaust valves had a white deposit. I assume this means it’s running lean and cooking the valves? Josh Hagger A A white deposit certainly suggests it is running a little lean, or may feasibly be just poor quality fuel. The most common cause of lean running is fitting a replacement air filter, changing the standard plastic cased type with an aftermarket pancake or cone type. These generally flow a great deal more air than the standard setup, particularly at cruising speeds. Way too many folks fit these filters then try to correct the fuelling by simply adjusting the jet. This is not the way to do it. It really needs to be checked and set up properly on a rolling road, as invariably a different fuel metering needle is required. Jet height adjustment should be kept to an absolute minimum just to tweak idle mixture, not to adjust overall fuelling. We have seen some jets that have been wound down to try and get the engine to run after fitting one of these pancake/cone type filters that they are some 5/8-inch down the jet tube! That’s way too much. If in doubt, get the car set up by an experienced tuner on a rolling road. The initial cost could save you from big bills in the long run.
Your air filter should be set up professionally.