Carb Question
Thread Starter
Instructor
Joined: Aug 2004
Posts: 177
Likes: 0
From: Windsor Ontario
Carb Question
Hi all. I took my 73 for a long run yesterday and averaged 16.5 mpg round trip (234 miles). I am wondering if I disconnect the vacuum line for the 4 bbl and plug it if it will make any difference in mileage? I was revving at 2900 rpm @ 70 mph and I was thinking that the 4 bbl might be opening and therefore using more gas than necessary. Is this possible?
Thanks in advance for your replies
Mike
Thanks in advance for your replies
Mike
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
if you have a q-jet and are talking about the vacuum line to the choke break (with a rod that goes to the secondary air valve), disconnecting the vacuum line will only hurt the cold running of the engine and allow the secondaryair valve to open quicker than it should (it will probally hesitate when they open also). the secondarys on a q-jet are only opened when the throttle is opened to between 1/2 to 7/8 throttle (different q-jets have different secondary opening angles of the primary throttle shaft).
a q-jet is not a vacuum secondary like a holley carb and even on a holley style vacuum secondary the secondarys are opened by venturi vacuum (air speed thru the venturis) not engine vacuum!
henry @ oles carb
a q-jet is not a vacuum secondary like a holley carb and even on a holley style vacuum secondary the secondarys are opened by venturi vacuum (air speed thru the venturis) not engine vacuum!
henry @ oles carb
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
At 2900 RPM your secondaries aren't opening. You would have to be going like 90 MPH at like 4000RPM before your secondaries would need to be opened. 16.5 smiles per gallon sounds about right for a 73...if you touch something it might reduce your mileage.
