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Carb Jet sizing question (EFI to carb conversion)

shotsy242 09.09.2014, 00:16

I built the following setup and I'm looking for a good baseline for carburator jets. I've got a wideband 02 setup on the car so dialing it in shouldnt be a problem. Just looking for where to start with the jets. The carb was something I traded for and rebuilt and I'm thinking the jets might be way off for my setup. Guess I should update my sig too!

Current setup is as follows

Carb Holley 4******0 cfm Double pumper with 4 corner idle
Current Jets
Primary 62
Secondary 76
Primary squirter is 28
Secondary squirter 28
Primary PV 4.5
Secondary PV 4.5

Motor 347 Stoker with Scat forged bottom end
Ford Racing Turbo-Swirl GT40X heads
Comp Cam XE274HR-12 PN 3******8
Gross Lift Int .555 Exh .565
Duration @ .050 in
Int 224 Exh 232
Lobe sep 112
Edelbrock RPM Air Gap intake
Duraspark II ignition with generic billit dist <-- Lame :-) but a start
Trans T5
Rear gears 3.73

Thanks for the advice, and yeah i mighgt be a dumbass but I wanted to get out of the computer/EFI business :-)

Thanks Shotsy!
circletrack5.0 09.09.2014, 11:56
since you have a power valve in both metering blocks, i'd get the jetting closer to square. 68 and 70 is where i'd start. you'd be better off with a 750 on a 347.
shotsy242 10.09.2014, 20:59
should I put a plug in the secondary Powervalve and then jet up to a 76 on that side. I cant find a 4******0CFM PN 4777-2 that has a secondary PV. I just put a new one in because one came out of the carb when I rebuilt it.
circletrack5.0 10.09.2014, 21:13 this and decide if it's right for your application.

edit: i don't remember any 650 i've owned having a secondary power valve.

shotsy242 11.09.2014, 00:50

Originally Posted by circletrack5.0: this and decide if it's right for your application.

edit: i don't remember any 650 i've owned having a secondary power valve.


Thanks Circletrack5.0 for the advice, so i'm beginning to wonder about the four corner idle. if this carb was just thrown together with misc. parts which it's beginning to look like would the 4 corner idle possibly be bullshit? perhaps someone just threw a primaty meetering block on the secondary side? Would the rear idle screw still impact the idle circut? I can get the part numbers off the base plate if that helps. so I guess in essence how do I tell if it's truely a 4 corner idle carb, I'm beginning to wonder.
circletrack5.0 11.09.2014, 11:42
4 corner idle is not uncommon. it does help idle quality on modified engines, usually on 750 and bigger carbs though. it is not on any 4777 from holley as far as i know. i've had a lot of 4777's over the years and none of them had 4 corner idle. put it on and try it. dial it in with the wideband and see if it's going to work for you. the 4 corner idle should help with initial throttle application too.
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