I see... kinda.
I must admit I've never noticed a lower rev limit in first or second (or neutral, come to that), but the speedo sender does feed the ignitor unit as well as the speedometer itself and I can't think of any other reason for it to do so… there's no ram air system that might justify modifying the advance for example.
If this is the device then it looks as if it requires the speedo sender to be in place anyway (presumably doubles the frequency of the pulses or something) this will make any speedometer read wrong which would be why they say it's not for road use.
I must admit I've never noticed a lower rev limit in first or second (or neutral, come to that), but the speedo sender does feed the ignitor unit as well as the speedometer itself and I can't think of any other reason for it to do so… there's no ram air system that might justify modifying the advance for example.
If this is the device then it looks as if it requires the speedo sender to be in place anyway (presumably doubles the frequency of the pulses or something) this will make any speedometer read wrong which would be why they say it's not for road use.