French racing blue aks400, left hooker, roundish light coloured logo on side heading west thru Eastergate, West Sussex just after lunch yesterday....

D reg blue and cream D*lly heading west on the A27 between Brighton and Eastbourne this afternoon.

I saw Mike in MVG in Littlehampton earlier.

All the heady power produced by 85psi of compression in 425cc pushing me up the road @ unbelievable speed!

Tailwind?

No - beans on toast!

And do you think 80-90psi compression is normal for a 425...? I'd have expected more...

When in doubt, have a look at a site discussing old motorcycle engines?

"There is a direct connection between compression ratios and the pressure thats read with a "gauge in the plug hole". Why wouldn't there be? Low ratio, low ultimate reading, High ratio, high reading. If this were not true how could a 18:1 diesel have 400 psi of compression? According to published tables,a healthy 6.5:1 CR should have 110 psi, 7:1-120, 7.5:1-130, 8:1-140 and so on. Always remember the throttle is to be wide open, as it varies the inlet air and therefore the compression. Also the speed at which you spin the engine should be spirited, as say the idle speed. This gives a truer reading of actual running, and shortens the time of leaking, the condition that would exist if the motor was really running."

In my experience, anything below 100 psi indicates that it's time to dig out the spanners and your wallet...

Thanks Ken, didn't know how to calculate psi from the CR. Yup I enheedened your prior advice -hot engine, loose tappets, open throttle, spun over with fully charged battery & good starter motor.

Will pull down the 2 'out of use' 425s I have and examine their bores etc. before putting money in Roy's pocket

Friday @ 1330 on M25, spotted a grey/cream 2cv traveling anticlockwise near junction 11 (Woking).

2CV on antiques road show as we speak......