guys,

ive got a 468 with a mighty demon 750. doing some more carb tuning. right now, i have the stock jets (75/83), squirters (31)... everything stock, but i have a 4.5 pv instead of 6.5

ive closed the butterflies a smidge under .020, idles at around 850-900, mix screws about 1/2 turn out from all in... secondary butterflies and idle mix screws turned in just a hair more than the primaries. floats set just under the middle line.

running about 21 initial, about 41 total, all in at 2500.

cam is 240@050 570 lift.

when i punch it in second from a rolling start the thing goes lean (narrowband autometer gauge) and stays lean. i get up in RPM pretty quick. third and fourth arent near as bad.

ive got that carter 172 gph mechanical pump on there... next time i go to the store im going to plum up a fuel pressure gauge to see if thats dropping.

what does this sound like to you guys? fuel pressure or do i just need to jet up in the secondaries? or something totally different??

also, the other night with friends in the car, i punched it in first and the thing kinda started shaking and quit pulling all together. didnt get a chance to look at the gauge, but i bet it way way lean...

ideas?

thanks guys

Are there jet extensions installed in the rear metering block?

what are jet extensions?

also, if i punch it in other gears, it goes lean too.

any ideas?

thanks

On holley style carbs if you accelerate really hard the fuel in the rear bowl will slosh back and can cause the rear jets to become uncovered causing a lean condition. Jet extensions are just adaptors that screw into the metering block and move the jets back about an inch into the bowl, this makes it so that when you accelerate hard the jets stay submerged in fuel. Here is picture of what they look like:
http://static.summitracing.com/global/images/prod/large/hly-122-5000.jpg

You need a notched float bowl aswell to run jet extesions so if your carb doesnt have them you need to buy the notched bowl if you buy the extensions.

Before you assume the carb is lean based on a narrow band AF meter try reading the plugs. You can't rely on a narrow band AF meter to determine what your AF is at WOT.

My car does the same thing (750 SPeed Demon and Autometer AF gauge) and with a wide band AF meter it shows 12.5:1. Those stock jets will be pretty close if you are near sea level.