AFM CO trim query

[Ozstyle]

Hi,
just thought I would check my throttle pot and AFM CO trim values as per the RPI web site. Throttle pot was out a bit, adjusted fine. Checked the CO trim and it was out a fair bit (3.1 V). Tried adjusting the screw on the side with allen key - screw turned easily but absolutley nothing, no affect at all on reading - (double checked instructions and connections).
Has anybody else come across this, did the factory fix the screw to stop tampering on some cars?
Just to add, Griffith 500, late 94, 5AM AFM and the car runs fine apart from very mild shunting at low revs, spark plugs mid brown in colour, no indication car is running rich.

Ozstyle

[Ballistic Banana]

Cant remember adjusting mine before only ever had to do the throttle pot. But have heard of them being cross threaded easily before, hope thats not the case. Does it wind down all the way? ( prehaps count down how many turns you do so you can return it).

BB

[pupp]

Mine (97 Chim) adjusts with a screwdriver and little movements seem to make a significant difference on measured outputs (and to running). The screw is on the upstream side of the AFM (ie facing the windscreen), fairly low on the AFM body

[Griffter]

You might find you have to turn it many times before you see any change - then the change can happen fairly rapidly. Mine was oringinally set to 0v and the car ran fine. No-one seems to have the definitive knowledge (or at least is prepared to release it) as regards exactly what this adjusts, and what effect it has on fuelling under what conditions.
Hence I have just booked a RR session to fiddle with it and find out!

[Cider Andy]

I'm sure you will have, but have you connected the meter to the correct terminals? It's the outside ones, the two furthest apart.

And this might seem like a silly question, but are you sure there is an adjustment screw? I have two 5AM meters, one has the casting undrilled, there's no screw.

[Ozstyle]

Thanks for the replies,
I've sorted it. I took the AFM off and had a good look, turned the screw a good few times clockwise but it just kept turning did not tighten up, also unscrewed it anticlockwise but just did the same. However I could hear something going on inside the AFM. Plugged it back up and checked the reading, now reading 0.00 V down from 3.1 V. I just turned the screw anticlockwise about 1 turn or so and adjusted to 1.8V as per RPI site instructions. I think I must have loosened something up whist turning the screw. Started the car up, it ran fine and seemed a little bit smoother but will go for a run tommorrow to see if it made any difference. So if anyone can't get any movement in the CO trim reading might be worth trying the above. I did notice a number engraved on the bottom of the AFM(same style as vin plate) - makes me think TVR do something to these AFM units but dont know what or why.

Ozstyle