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
>
IF your car has a working positive crankcase ventalition system
then the answer is quite simple... You already stated that your car was
running abit on the rich side. When you opened the crank-case to the
atmosphere you allowed O2 (oxygen) in to the crank-case, this O2 was then
pulled in to the combustion chambers via the pcv valve. This added O2 was
just what the car was in need of, and the engine thanked you and showed
it's joy in finally reaching an air/fuel ratio that was somewhere close to
correct by increasing in rpm.
Lex
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