Jay, the next time you have the manifold off just drill 1/4" holes in you plugs, it restricts the flow while still letting the choke work, I did this on my SportWagon
"When driving on the interstate I have to give it ALOT of extra throttle to increase the speed just because the current power valve is not engaging until you open the throttle alot more." A classic symptom of too little intake velocity is poor throttle responce. Does anyone have the CFM figures for the 750 Qjet primaries?
The reason I have to open the throttle so much to get extra power is because the power valve is not engaging until I open the throttle so the vacuum is low enough to open the power valve.
You need a good Quadrajet or a Holley 650 spreadbore double pumper. Squarebore double pumpers have rich main jetting and small power valve restrictions so your idle and cruise mixtures are too rich.
I was thinking about the 650 DP Spreadbore also. If you're dead set on a Holley, then I have two 650 DP Spreadbores (#6210-3) that I will sell you cheap. I also have a rebuild kit for it with 6.5 powervalves.
Ouch,that could cause a lot of fuel to be wasted just to keep it running until it gets warmed up. My .02
Do not bother with a 650 cfm carb... It will kill the performance over 4000 rpm, even with a stock engine... Stock carb is 750 cfm.
The stock carb is rated at 750cfm at WOT, which isn't exactly the ideal right foot setting for mpg. Now that that's settled, what difference would it make what size carburetor is on the car if you're only operating on the primaries? Just a thought. My car gets 15mpg with a 750 Holley if I behave myself. I haven't check the mileage at WOT but my best guess is that it would suffer a bit.
Well I am sure that although he wants better fuel milage he still wants his WOT performance so why ruin that? A square bore carb has lower air fuel velocity at low throttle due to the larger primaries, which kills fuel milage. The q jet is the best fuel milage carb anyways due partly to the spread bore design with smaller primaries that give high air/fuel velocity at low throttle.
Get a 650 spreadbore holley with a 4hole spacer. Make sure the power valve is not comming in as the overdrive at 70mph may be on the edge of inrichment. Put more vac advance to it for crusing. (Don't over advance the max mechanical timing or your engine may suffer.) Install soft springs on the mechanical weights for more low rpm cruise advance. A Q-jet is far superior for mpg though. My 67 ElCamino 275 HP 327 Q-jet got 23-24mpg on trips with a 700R4 and 3.08 gear. A friends 57 Chev 327 Q-jet got 24mpg crusing with 700R4. My speedo/odometer was set to interstate mileposts for correct calculation on 100 mile stretch.
Gas mileage around town has decreased if anything. I don't have hard numbers, but definitely no dramatic improvement. However, the car runs way better with the Q-Jet than the Holley.
Adjust the ATP properly or the whole idea is moot. Best to use AF meter such as www.fast.comhttp://www.fuelairspark.com/Products/details/meter/alcohol.asp
