Rev counter problems

[Justin1969]

Hello to all. Here's a strange one to me. I wonder if anyone can shed some light on this. I've just started up my elan after it sitting for around 6 months. Started 1st time.
Once started there was a buzzing noise coming from the instrument panel. This lasted 2 or 3 mins. Once engine warmed up I began to rev the car a little. The Rev counter stuck at 5 - 6 revs. Reving again it started to work again. This happened after a few revs several times before I turned it off.
Any ideas anyone to point me in the right directions??
Thank you in advance as I know I always get great advice here.
Regards Justin