I have a 6400 mile Pettit ported engine My vaccum at idle is -13 lbs. constant. However when I am decellerating the negative pressure can go to -19 to -21. I have been reding on other posts that it should be -17 to -20 at idle. Is this normal? I checked and double checked the vac lines for any loose ones and all is good.

 

that is only for stock, ported engines will be less, becasue they flow better. Call pettit they will know.

 

i have a ported motor by Farrel , and I get a vac. pressure ~13-14. I wouldn't worry, your numbers look ok.

 

So what if the vac pressures are low??? what does that mean?