hey guys



well i am trying to improve the gas milage of my 84z as much as possible so to that end i am attempting to lean out the primaries. so today i swapped out the 65 primary jets in favor of some 63's and at the same time switched from 6.5 to and 8.5 power valve. now i have a hesitation/stumble at certain times at first it was off the line but moving the accelrator pump cam to the 1 position now it is just during transistion from cruise to heavy accel, ( i have a vacuum gauge hooked up basicly from what i can tell it ocurs and rougly 6-8 inhg ) this sound like the power valve is coming on to early that would be my guess. by the way idle in gear is 12-13" and cuise is 16" and high way is 18 or so. mild cam headers 3.73's performer manifold. thanks for the help. look ing for guys with more expertise with carbs thanks

 

car is and auto too sorry forgot that part timing is 10* intitial light and i installed the lightest springs for advance.

 

The primary jets are too small. Increase them until the stumble gors away.

 

i'm pretty sure the higher the power valve the sooner it opens

 

the 8.5 will start to open at 8.5 compared to the 6.5 8.5 will not give better gas millage in most cases. Try going back to a 6.5 might get rid of that hesitation. Would not go leaner without a good of running rich. check your plugs and the color and it will tell you how much leaner you can go if any at all. If your too lean, richer can improve mpg.

 

Dude, not to be the bearer of bad news, but a holley will not get good mileage. You are much better off to get a quadrajet because the primaries or so much smaller. I bet you you will get way better mileage with a quad than a holley. Just my thought.

 

Properly tuned you can get decent mpg with a holley. Probably not quite as good as others but not nessasarly bad. i get 20 mpg on highway and 16 around town with my Holley DP and in the 12's its all good enough for me. Oh and thats with 3.73's

 

Thats way better than I have ever heard with a double pump. Also the smaller the powervalve, the less pressure it needs to open. For example, a high duration cam like 290 or more does not build much vaccum at idle or anywhere else for that matter. You need a smaller numbered powervalve. With my 294 cam I ran a 3.5 powervalve. Also a good rule of thumb for small blocks are 68 primary and 70 secondary. If you are running 63s, I believe that to be too lean, but it will give you better mileage.

 

Check your accel pump and make sure it adjuted right..015 to .020 more pumparm movement @ WOT