Define the right heat range

Although some people may not agree, to define the right heat range of your spark plug is essential for the good performance of your Puch Maxi. The general rule I love to use is, the more rolls per minute your Puch is processing, the colder the heat range needs to be. 

Which heat range your current spark plug has, is always mentioned on the spark plug. However, each manufacturer uses it’s own way of defining the heat range. For example, in case of the NGK spark plugs, the rule is:

  • the lower the number; the hotter the heat range
  • the higher the number, the colder the heat range

In case of the spark plugs of Bosch, it’s the other way around:

  • the lower the number, the colder the heat range
  • the higher the number, the hotter the heat range

How to define the right heat range for your Puch Maxi?

After doing a lot of research and asking a lot of Puch experts their opinion, we created a short tabel with the type of cilinder, the heat range, the brand and the indication mentioned on the spark plug. This will help you a lot to define the right heat range of your Puch Maxi.


Cilinder Warm / Cold Heat Range NGK Bosch
50cc Warm 5 NGK B5HS Bosch W8AC
50cc fast Warm






Bosch W7AC

Bosch W5AC

60-70cc Normal 7 NGK B7HS Bosch W5AC
70cc fast Cold






Bosch W4AC


Is this really so important? 

Yes! To show you the importance of it, I will share you my own experience. A few months ago my Puch Maxi was having troubles at full speed. When I was driving at full speed, my Puch maxi made a ‘stuttering’ sound. Really bizar and probably not good for my beautiful lady.

This was during summer and autumn. When winter arrived and the temperature dropped significantly, my Puch Maxi didn’t even start anymore (drama!). This came as a big surprise, because my lady always started in a few seconds. So I tried several things… But the problem only disappeared when I defined the right heat range and I changed the heat range of my spark plug. And guess what, my Puch maxi didn’t start because of the fact that I was having the wrong heat range! I replaced it with a Bosch W8AC (which is a warm spark plug) and it started immediately. In addition to that, the stuttering at high speed was also gone. So yes, to define the right heat range is important :-).



Don’t be stupid, do the investment

After doing a lot of research, I noticed that a lot of people experienced serious damage to their engine because of not using the right heat range. So don’t be stupid and spend of a few euro’s / dollar’s on the right spark plug and avoid this kind of trouble now or in the future. If you define the right heat range of you spark plug today, I can guarantee you that you will avoid a lot of trouble later.


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