I'll take a guess... If you had a really really worn intake valve,
opening the valve cover allows fresh air into the cover which could be
sucked into the cylinder on the intake stroke through the intake valve guide.
This would cause the rpm to go up just like having a vacuum leak. ?????
Second guess:
Your breather system is cloggedand opening the valve cover helped breath
a little?????
No, I don't either of those is right. Anyone else want to take a stab at it?
Chris
On Fri, 29 Sep 1995, F. van Dalen wrote:
> I spent part of this summer's vacation in France, trying to keep up with
> with a friend in a Westfield Seven. One day we stood bent over my B's engine
> compartment admiring a knocking sound from what is presumably a worn valve
> guide, when on an impulse my friend lifted the oil filler cap to improve the
> sound quality. What happened then is unspectacular but I just can't figure it
> out: we got a very noticable increase in RPM. How the heck is that possible?
> I had one carburettor running too rich at the time, but apart from the one
>valve
> the engine is performing very nicely. I don't have compression readings, but
> considering the car easily reaches 90 mph I assume compression is OK.
>
> I don't think there is an actual problem here, but I'm just dying to know why
> lifting the cap increases RPM. Any comments welcome,
>
> Frank
>
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