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TR4/4A Tr4a rpm, with or w/o PCV

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R

Rrbbeerrttoo

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Opinions please,
While investigating fuel mixture problem, I noticed the engine rpm increases to about 1050 from idle speed of 700 when I remove the oil filler cap on the rocker cover. And it increases again to 1300 rpm w/o ALSO the PCV cover and associated guts. Air filters were off. Are these changes in RPM normal? Thanks for any comments. Robert
 
Some change is certainly normal. The PCV valve tries to pull a partial vacuum on the crankcase, so removing the oil cap increases the airflow through the valve, in effect a vacuum leak.

But if the mixture was right, I'd expect it to stumble and lose rpm (even die) with the PCV disassembled. Sounds like you are running rich (which is probably the mixture problem you were looking for).
 
TR3driver,

Ummmh, thank you. Your reasoning sound logical. After all these years I've had only one carb. mixture problem and I could not figure it out....dummy me. Thanks again!
 
Still not sure what I have now.
I believe that the mixture problem may be resolved because the carbs now act as the manual says. About the other issue, opening the pcv valve or the oil filler cap still causes engine rpm to increase 300 rpm or so. overall, the car drives great although have not check fuel comsumption.
Robert
 
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