Good news, i’m Glad at least one of my suggestions has “borne fruit”.

I would not refit a coarse filter on the pick up - simply fit a generic in-line filter in the fuel line to the pump in a place easy to monitor the fuel flow (use a clear plastic filter) and easy to change if it becomes blocked.
These type of filters are routinely stocked by car parts stockists, accessory shops or motor factors.

The difference between the two Renix units lies in the internal ignition timing map held in the EPROM. The correct version for the B172k (1987 yr.mod.on) engine is indeed the “415” which gives a timing advance of 6deg at a speed of 15 r/s (900rpm) and 14deg at a speed of 42 r/s (2500rpm).
The type “408” hold a map suitable for the B200E (fuel injected 2lt) and gives an advance of 12deg at 900rpm and 30deg! at 2500rpm. giving much further advances across the board.
The lack of a knock sensor in the B172 engine management system leaves it open to damaging high speed “knock” (pre-ignition) which may well be inaudible and could prove damaging - especially causing erosion of the piston crowns.
The type 408 also includes an rpm limiter (around 5600 from memory - though I could well be wrong).

Mac.

Always interested in old renix units which work (!!) but postage from Finland might be pricey. What numbers do you have?

There is a review/summary on here somewhere for the ignition modules. Mainly differing by advance. It would best to keep the same one.

Good trouble shooting!

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The pictures look better on a phone. Need to get the MACster a paid photobucket account.