Try unplugging it and see if any difference, this can often show a difference, albeit with more smoke coming out of the exhaust.
I have one of the early Ron Tuning boxes (used) which increases the power(BHP)and is easily fitted, many reviews on Forum.
£40 inc P&P. Obviously it isn't going to give you the 160/170BHP the maximum safely available from this engine, but it does make quiet a difference to either the 115 or 131BHP engines, if yours is the lower power unit, this can be brought up to the 131BHP spec again quiet easily. Raistlin (Paul)for one may be able to add more to this as will others.
"My lovely car now sold onto a very happy new owner.
I still love this marque and I will still be around, preferred selling to breaking, as a great runner and performer"