I opened the airbox today (on the way to take the motor out) and I saw that the rubber trumpets had been cut short (I dont know what normal ones look like besides in the parts catalogue).. it seems a normal trumpet has two horizontal ridges and then the final edge / opening... mine has been cut off at the second ridge (ie shortened by about a third). I spoke to the guy who owned the bike before me and he said they found that it increased the HP slightly which is possible because it seems that the full length ones would sit very close to the air filter. My concern is that I have a 1970 Alfa with side draught webers and I know that the length of the trumpets can affect performance (I cant remember which way around at the moment but the length which gives high rpm performance negatively affects low rpm performance... ie its a trade off)... Has anyone shorterned their trumpets on their bike? Is this a recognised NC mod... any negatives? (one positive is that I see the one trumpet wasnt seated properly and was reducing the carb inlet size so maybe a little better flow to come).... BTW the previous owner said the bike ran 59 HP this way

It is not a recognised mod and you are right to be concerned that they are not going to be ideal for your bike.

The length of the trumpets does affect their "sweet spot" - shorter has a better high revs performance.

The "HRC" carb settings for the bikes has a very short trumpet and various other vital settings to make it work - no airbox for starters!

Some full length trumpets would make your bike better I am sure.

Thanks.. is it still possible to buy full length / new ones? If so where?

Drop me an PM if you want some full length NC30 trumpets, I've got a spare set. Can have them on their way to you om Tuesday