Smiths rev counter reading incorrect. Likely reason ?

[Moto]

Anybody help me with this one.

I put the Vixen on a RR last month and asked them to check accuracy of the rev counter as I was sure it was reading low at max revs. The result is that it is accurate up to 4,000 rpm but then starts under reading on an incremental % until at 6,000 rpm it's reading 5,500rpm.

The unit is a Smiths Ford type RV1 which I understand is not OE.

The unit shorted out and was rebuilt by JDO instruments 18 months ago and upgraded to work correctly with electronic ignition.

I don't know if the incorrect reading fault was there or not before the rebuild.

The car has also since been rewired with the voltage stabiliser becoming redundant and removed - not sure if this may affect it.

The car has a basic Accuspark electronic ignition unit which just replaces the points.

Any ideas on the possible cause as I'm not sure where the right place is to start on this ?

Moto

[phillpot]

Live with it........ Just remember your 'red line' is now 5500

[P100]

I had similar issues with mine..
Because I had just rebuilt the twincam, I decided that I couldn't trust it to give me the correct info when I needed it. I did a fair bit of research and eventually went for a Racetech electronic tacho with a smooth cut rev limiter.
The diameter was too small for the dash cut out so I had the local engineering co plasma cut me a converter ring in satin stainless to allow it to be fitted.
It actually looks good and is nice a clear to read too.

Roy

[startStop]

I'd have a word with the people who did the rebuild.

I think it's often the case that becaue of the movement, a compromie between low and high rev accuracy may be needed. Perhaps they didn't think you'd be redlining?

Dom

[Moto]

I spoke with JDO and they were very helpful. Dom, you were spot on. They can be adjusted for accuracy but at a specific rpm and as a standard this is done for idle, not redlining. So I'll just live with it but at least I now know.

Moto