Here's some info on plugs, very general in nature.

Have you ever wondered what makes a plug "cold" or "hot"?

It actually has nothing to do with the spark itself. The spark on a hot plug is not hotter, per se, than a spark on a colder plug. What is hotter or colder is the temperature range at which the tip tends to stay after the engine is warmed up. This is determined by the rate at which the electrode and ceramic stem conduct heat away from the tip where the spark and ignition of the compressed fuel/air mix is happening. A look at the cylinder end of a plug reveals a recess, like a castle moat around the ceramic stem and electrode. Simply speaking, the deeper the "moat" is, the slower heat is conducted away from the sparking tip and into the body of the plug. A really hot plug has a very deep moat, a really cold plug has a shallow moat.

The reason plugs are offered in a range of heats is to be able to match them to the thermal characteristics of a particular engine. Desired is a plug tip temperature hot enough to burn off crud, so the plug doesn't short out via the crud or foul, as they say. If a plug is too hot at the tip, it could cause damage to the plug itself, or possibly the piston crown. In a trials bike this is very rare, as they are not run wide open for miles and miles. For this reason you can run just about any plug in a trials bike if you are in a pinch. The very hottest commonly available plugs will rarely, if ever, do anything bad to the bike. The exception would be if you have some other problem with the bike, such as a very lean condition, an air leak, or way too much oil in the gas, which will - surprise! - make the bike run lean and be more likely to ping.

If you have problems fouling plugs, feel quite free to stick in one of the hotter ones available, like an N12YC Champion (higher numbers are hotter), or a B5ES or BP5ES NGK (P here means the plug tip is extented more, and lower numbers are hotter). Unless you plan to do some road racing with your Beta, don't worry about it. There is no point, however, in putting in a really hot plug unless you are having problems with fouling.

Ever had a problem starting your trials bike, where it took a bunch of kicks to light it off, whether or not it is hot or cold? One possible fix for you is to reduce the plug gap. Out of the box, most plugs used in trials bike come set at about .030" or about .7 mm, or more. Some trials bikes have ignition systems that do not produce enough energy at kick-starting RPM's to breach this gap all of the time. Regap the plug to .020 to .025" or .5 to .6 mm. This may fix your mystery starting problem.

My new Fantic uses an inky dinky european racing plug not available in any auto parts store. It's the usual 14mm thread, but the body above the thread is much smaller than usual. Thankfully, my `96 Fantic is jetted very close to perfect stock, which has been a big surprise to me. I wonder how long that dinky plug will last?

-CJ