Carb tuning help

moper said:

Notice there is no difference in the size of that hole that passes fuel from the 390cfm to the 950HP. There could be 30 or more jet numbers difference in the carbs, but the PV is the same size hole?

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Moper are you referring to the power valve channel restrictors? If so have you ever measured them or just eyeballed them? I have measured them on several different carbs and have found differences in the PVCR sizes. I've measured them from .035"~.060". There are billet metering blocks on the market that allows you to change the sizes of them to find that proper flat fuel curve.

fishy68 said:

Moper are you referring to the power valve channel restrictors? If so have you ever measured them or just eyeballed them? I have measured them on several different carbs and have found differences in the PVCR sizes. I've measured them from .035"~.060". There are billet metering blocks on the market that allows you to change the sizes of them to find that proper flat fuel curve.

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Exactly.

Moper, I don't know where you got that info that ALL the PVRC holes are the same size, i've worked with many holleys, they are not all the same size, like i've said & will stick to it, Holleys are the most tuneable over other carbs, you just need to understand how they work, we can go on & on, & in the end, if you learn how to tune them, you'll be very happy with them, they are not rocket sience, also as sake of arguement, if the float levels are off on a carter, they too will not work right, most know that, & have exsperience it time after time, same goes for any carb, you need a certain level of fuel in any carb to properly meter the air/fuel, if its too low/high, it interupts the metering. Its fine that you like carters, i like holleys, & most lickly always will, i said it before, & i'll say it again, i HATED holleys back when, that was only because i didn't take the time to understand them, or try & tune them, but when i got lucky with one that worked great on my combo, i was a believer, so i got my act together & read as many holley tuneing books as possible, then got after it, the end results were a ++++, maybe i need to start with an eddy 750 AFB, see if i can fix there quirks.

hmmmm.. i opened a few old carbs just today.. checked if it was.. i fond all of the metringblocks i had was the same size.. exept for a pretty new 750.. no i had 4 650 mtringblocks 2 750.. and 1 850.. all metringblocks had same pvr holes.. mystical.. i think maybe u gys are refering to some aftermarket or the newer, maybe bigger like dominators have larger?.. mainly the hole in the pvr itself are alot smaller than the 1 in the block.. but its the spring tention that is different and u could tune the amount of vacum needed by changing the pvr

NorwayCuda69 said:

hmmmm.. i opened a few old carbs just today.. checked if it was.. i fond all of the metringblocks i had was the same size.. exept for a pretty new 750.. no i had 4 650 mtringblocks 2 750.. and 1 850.. all metringblocks had same pvr holes.. mystical.. i think maybe u gys are refering to some aftermarket or the newer, maybe bigger like dominators have larger?.. mainly the hole in the pvr itself are alot smaller than the 1 in the block.. but its the spring tention that is different and u could tune the amount of vacum needed by changing the pvr

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I've ran across some that are the same but I guarantee you all are not the same as you saw by the one 750 that is different and I didn't mix them up with a Dominator or aftermarket block cause I have never even had a dominator in my hands. How did you measure the PVCR size? I measured them with numbered drill bits that I mic'd to make sure of their actual size so I know their not the same on all 750 carbs which is all I have ever checked them on. I have a log of every one I did along with the list numbers. I will note that even though they were all 750 carbs they were different list numbers. i.e. 4779, 4779-1, 4779-3, 4779-5, 3310-3, 1850. In fact not even one of the carbs I just listed had exactly the same size PVCR's. Some were pretty close but still not the same.

On adverage, i've found the PVRCs as tight as .025", but most were .031"/,033", on advarage, the emulsion holes are .031", but these shouldn't really be messed with unless your really fine tuneing, however, you could drill/tap them & install screw-ins, & even add more like found on aftermarket MBs, but really should be left to the pros, most of your emission holley have emulsion "tubes" under the cap, there the restrictor, slide them out, increase the PVRCs to .031"/,032", increase the IFRs about .003", some are on the top of the channel, doing this will normally make the MB moore perf. orientaded, install screw-in ABs. This is one i did, figured it would be one of a kind, its the 800dp Spread bore, installed screw-in ABs, should have went all the way & made it 4 corner idle too.

Jay_340 said:

Hey all. I have a 71 Duster with a mild 360. It has about 9.8:1 c.r. mildly ported J heads, a Lunati Voodoo cam with 268/276 adv. duration, 226/234 duration @ .050" and .494/.513" lift, Eddy Performer RPM intake, stock 340 HP manifolds and 2-1/4" exhaust with Magnaflow mufflers. I have two different carbs, an Edelbrock 600 AFB style and a Holley 650 double pumper. The Holley makes this car an animal, no hesitations, power from bottom to top of the tach, but its lacking in street manners. The Eddy 600 has very good street manners, great off-idle transition, but it starts pinging hard after getting up in the rev range. I put in richer metering rods, but it still pings. Either I need to jet it up more, or get a bigger carb if I want to keep with the style of the Carterbrock. Does anyone have good experience tuning the AFBs? If I need a bigger carb, then I'll use the Holley. If I can tune the AFB a little better, I kinda want to keep it on there. Help a guy out, who knows the AFB?

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Your 360 really needs more cfm 750-800cfm for maximum performance. Mopar 1974 360HP motors came stock with an 850cfm Thermoquad. For your combo the 750 cfm Edelbrock 1407 out of the box would be just about perfect. Swap the stock 71/47 metering rods to 73/52's and bump your timing to 18 degrees intial if it's not already there. I have the pump arm in the middle hole and idle mix screws out about 1-1/4" turns on my combo. Excellent idle and responsiveness from the carb. My carb/setup has no dead spot off idle or anywhere.