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Old 04-26-2021, 06:39 PM   #1
blkmonday
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Carb suggestion for big block olds

I have a 66 olds dynamic 88 with a 425 currently with an edelbrock performer carb and manifold. Mild Crane cam bored 30 over and a Taylor HEI ignition. Have never been too thrilled with the carb. My knowledge of carbs is weak. Carb was rebuilt about 2 years ago. Last year I had a local shop dial it in and get the timing dialed in as well. They said they disliked the carb but didn't elaborate. Took car out of storage today since November. Car starts and ran good for awhile but has a rough idle. I'm thinking king my carb is gummed up a bit. I didn't use stabilizer because I figured I'd run it during the winter...but I didn't. Anyways......what would you suggest for a carb? Hoping for plug n play. It's a spread bore manifold. Saw rebuilt Rochesters on Jegs.com for a good price...is that a step up? How much adjusting will it need out of the box or should it be good to go? Any info appreciated
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Old 04-26-2021, 09:12 PM   #2
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Re: Carb suggestion for big block olds

A Rocheester 4MC/4MV is tough to beat. They have very good primary control - much better than Holley 4150s and usually better than a Carter AFB/ThermoQuad. The secondary can be adjusted fairly easily with metering rods, rod cam, and spring windup. A "plain/early" 4MC can flow 750 CFM without any modification. A "later" (after about 1971) 4MC can flow over 800 CFM.

They also require an intake which will accept the bore pattern. If you have a spread bore intake with equally sized bores, you may want to consider a Carter AFB instead, or change the intake. The Carter is a lot more configurable and stable than a Holley. Edelbrock offers new "clones" based upon the AFB design, but you will probably have a lot more adjustment involving all four jets and all the metering rods, in addition to the usual adjustments.

No carburetor out of the box is a "bolt-on" without adjustment. At a minimum the idle mixture will need to be set, and usually it is prudent to check the float level. It is very common to have to change at least the secondary jets (and metering rods) to tune for the specific engine.

It may also be reasonable to clean out and freshen up the current carb, if it is still viable.
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Old 04-27-2021, 05:14 AM   #3
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Re: Carb suggestion for big block olds

What are your thoughts on the edelbrock performer carbs and the rebuilt quadrojets from Jegs? I'm going to try and clean up my existing Edelbrock for now and see if it helps
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Old 04-27-2021, 09:41 AM   #4
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Re: Carb suggestion for big block olds

hey blkmonday; Bowtie is right on-- QJet is something that GM just did right.. they threw it on everything from a baby 262 to a Poncho 455, and it took it.. and that 425 of yours probably puts out some under hood temps, so the spreadbore carb would better suit your big block and manifold.. and his option of the AFB or ThermoQuad is another good option for an econo carb (like a Qjet), until you mash the pedal, secondaries dump, and that 'waste gas and go fast' becomes the option..
but seriously, while i would recommend the Q or AFB, i have used and liked the squarebore edelbrock's.. you didn't say what series, but even the smallest (1403?) 500cfm manual or electric choke is probably more than enough for your limited street use.. you mentioned a few years ago you had it timed and 'dialed in', and i am sorry that your shop did not elaborate why they disliked performer, but if ever their was a close to "plug n play", it would be the performer.. while it will limit the Super Rocket 88 you've got, it is still powerful enough, and a fuel saver, and (nothing against Holley, i love them too); once it is "dialed in"; your done, no power valves blown, leaky fuel bowls and buna tubes, etc..
before you spend $300-400 for a new performance carb (and yea, if it were mine, i would be gettin the 1903 edelbrock Q, BUT-) you might first just change fuel filter (you mentioned you never fired it up over winter), spray the carb full of Berryman B-12, buy some B-12 to dump in the tank, with some 91+ premium, and then think about a $20
phenolic spacer from Mr.Gasket or TransDapt; or even a $2 piece of pine (racers were building spacer/gaskets before speed companies caught up in the 60/70s; don't believe me? go to your jegs and search wood carb spacer) and some extended studs from Fastenal (right there in stratford; or the nutty co. guys down in milford); as i think the biggest hinderance in the carb (you mentioned you were never 'too thrilled') is partial vapor lock.. lift it away and separate from the massive heat of the block to allow the fuel to come in more cool and dense; and the berryman should help get some varnish out, and i am sure the filter is gunked up after six months of sitting..
-- while i am with Blue Bowtie as far as eventually going bigger to either Rochester or Carter; you can still get life out of that 500/600 (1403/1406-7) cfm Edelbrock, just lift it a little; .5"-1" you should see crisper response, more stable idle, no loss in mpg (unless foot gets heavy, haha) hope this helps..
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Old 04-28-2021, 04:11 PM   #5
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Re: Carb suggestion for big block olds

Wow thanks guys..great info! The current Edelbrock Performer is actually the 1407 speadbore with manual choke. took a quick look at it today. I have one of those clear glass filters and it indeed looks a little gunked up. Im going to take your advice use some B12 for a cleanup as i really think its just got some gunk in there. Im going to check the fuel pressure from the pump as well. I replaced a dead pump a year or two ago. pretty sure the new pump was a brand new Carter....also I have one of those Mr Gasket spacers withe the metal heat shields kicking around my garage. i never used it because i was worried about hood clearance but maybe (if i can locate it) Ill see if i could use it. in the meantime a good B12 clean and a new filter.....what should the fuel pump be running pressure wise just in case?
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Old 04-28-2021, 05:41 PM   #6
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Re: Carb suggestion for big block olds

that 1407 can flow 750+cfm when tuned.. that is more than enough; even at your altitude.. (i still love a good Rochester, but back when edelbrock were putting together their dyno packaged performer 'power packages' line of carb/manifold/cam/lifter/heads, etc.., they spent millions in dollars and hours of dyno and field tests to insure when they posted dyno results, it was VERY close to what a DIYer could roll out the garage with hand tools)

if your 425 was like my 403Rocket, you should see 5-7psi..
if it was a performance (hi-volume or hi-pressure carter/holley) pump, you may see 8-12? tops; unless you add an electric pusher pump, then you would push into teens/twenties..

as far as clearance; cheap trick (not the band), flip the air filter lid over..
still creates dust seal on top of element, but can give you an extra 1+" in clearance, as the dome of lid rides inside filter, instead of above..

also, some 4.5/4.9 cadillacs used 3" risers in between the carb and element, so the OEM filters cases were inverted parabolic; and dropped over the carb.. (if you track one down in salvage, or buy an aftermarket; just insure it clears all linkages)

and if you don't want to drain the bad gas out of tank (i wouldn't), don't forget to add some premium to tank, or B12, or BG44K; otherwise you'll be going through alot of nylon fuel elements..
hope this helps..
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Old 05-06-2021, 05:08 PM   #7
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Re: Carb suggestion for big block olds

Had some time to pull the carb today. Cleaned up nice with the B12..strong stuff. However I think I found the problem. When I pulled the filter (it's one of those I line glass ones with the changeable filter inside) there was a lot of rust in it. I'm thinking my gas tank is full of rust. Any experience or suggestions on what to do? Online search turns up a few things. I'm not against a new gas tank if I could find one, another quick search didn't turn up anything. There are cleaner/sealer kits but the tank has to be drained and pulled and flushed (doesn't sound like much fun) but I guess it takes the risk of getting the fuel system plugged up on the side of the road.
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Old 05-06-2021, 06:20 PM   #8
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Re: Carb suggestion for big block olds

There may also be a small filter in the carb inlet fitting, often overlooked.
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Old 05-06-2021, 08:42 PM   #9
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Re: Carb suggestion for big block olds

1. Spectra Premium out of canada has done OEM steel tanks since the 70s; they may have replacement..
2. if too expensive, look at a local 'classic' GM salvage yard; many 60/70s used the same (or similar) 20gal. tank with same saddle clamp/straps..
3. AND- if just weekend warrior, not daily driver, or over-the-road cruiser; you could just get a universal plastic fuel cell for trunk mounting, and drop the metal one at your leisure, or leave in place, and just drain and leave fuel cap off..
i have used the liquid cleaner/sealer kits you refer to.. they are good, as it puts a plastic liner in the tank (much like the plastic liners put into food/beer cans to keep product from absorbing aluminum/tin taste) and is just as good as new replacement; and usually more affordable than new tank..
some options, hope it helps..
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Old 05-07-2021, 09:13 PM   #10
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Re: Carb suggestion for big block olds

There is no rule against installing additional inline fuel filters in the line from the pump to the carb. If you catch all the rust before it gets to the carb, and eventually clean out the tank of free metal, it could be fine with one inline filter - Eventually.
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