fiesta mk 3 oil breather pipe mystery

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Sat 13 Jan 2007 15:33
fiesta mk 3 oil breather pipe mystery - milkyjoe
hi, if i have the engine ticking over at normal operating temp and then if i squeeze the oil breather pipe betwix thumb and index finger the revs increase
slightly is this normal? surely a squeezed pipe is not doing its job but the engine rev increase surely denotes more efficient combustion or am i missing something in this equasion?
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Sat 13 Jan 2007 20:50
fiesta mk 3 oil breather pipe mystery - mfarrow
I'm guessing the 'blockage' increases the crankcase pressure which means the piston has to do less work to get to the top of compression.

I'll try it on my car if I have the chance.

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Mike Farrow
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Sun 14 Jan 2007 14:12
fiesta mk 3 oil breather pipe mystery - none
Well, I'd guess that the engine is a bit worn. On older carb fuelled engines, the idling mixture was adjusted with the breather system in place. The adjustment then took into account the crankcase fumes passing into the inlet manifold, also, any minor air leaks in the breather system were 'adjusted out' with the mixture screw. If the breather system is disabled (squeezed) after adjustment, the idling mixture will change, and so will the idle speed.
Worn engines create more crankcase pressure and fumes than unworn ones, and the effect is more pronounced.
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