I almost too embarrased to ask, but what do the pre-chambers do? Do they go bad or wear out? How can you tell? What are the symptoms of a bad pre-chamber in a running engine?
Zane

One thing they are supposed to do is spread out the fuel.. ours have 7 tiny holes through which the injectors are supposed to shoot the fuel out...but the precombustion chamber is where the glow plug resides... so it can help ignite the fuel on the way out into the combustion chamber when the engine ( especially the cylinder walls)are cold and the compression is low due either to worn rings or slow cranking speed...( the rate of compression affects the temperature the air gets to as the result of the compression stroke).
Bad mileage and hard starting are some of the problems which will result from a problem in the preCChambers.... they can get blocked with carbon build up, they can have pieces of glowplug drop into the cavity...
I have a carb Briggs and Stratton engine from pre WW2 which has one also....