Holley guru's- need advice

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mopowers

mopowers

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I have an older Holley 4779-2 750 DP that was used on my uncle's 8 sec slingshot. Im trying to convert it back to stock to run on my 340 by rebuilding it and replacing the parts that came stock on a 4779 carb (jets, power valve, squirters, etc... I noticed the outer air bleeds appear to have been drilled out. Will this cause a problem when I go to tune it for my 340?? Can tuning the air/fuel mixture screws compensate for the larger air bleeds? Would I be better off just buying a new proform 750 main body, trying it the way it is, or drilling and tapping for screw in air bleeds?

Thanks for the advice!
 
If you are running a stock 340 that will be too much carb and will cause you a lot of grief trying to get the car to run properly.
 
That carb was recommended to me by Brian at IMM engines. I'm getting ready to have him set me up with a set of RHS heads and a nice solid lifter cam. He said to use a 750dp/RPM airgap w/ a 1" spacer. I trust what he says. Just trying to put this carb back to a stock setting so it'll be tuneable once the changes are made.
 
Brian recommended a modified carb off a drag car or did he recommend you use a 4779? I'm pretty sure the recommendation was for a box stock carb as they work well.

I have a 4779 here that looks nothing like an OOTB carb, doesn't meter fuel like one either.

If the carb you have has been monkeyed with, there's no telling what you are going to end up with. Drilling the idle air bleeds leans that circuit.

If you got it cheap enough, buy a proform body and start fresh with the suggested tune up.
 
Brian recommended a 750 DP. The one I have happens to have been modified. So what??? All of the modifications can be reversed. I just don't know much about air bleeds. That's why I was asking. The carb was inherited when my uncle passed away last year. I think it would be cool if I was able to get it to work on my car. I know what jets/squirters/power valves come stock on a 4779. I just need to figure out the air bleed situation.

Just lookin for help, man. That's all. What's the harm in trying it and if I can't get it right, proform, hear we come...
 
Sorry if you took my post wrong. Wasn't my intention.

Your question is very close to this... What color shirt am I wearing today?

You can guess and will likely be wrong. Same with the carb. Unless you measure every air bleed, emulsion hole, PVCR, etc.. nobody is going to be able to say, yeah that will work. If it works OK, bonus

If you are a good carb tuner, have at it. If not, buy a proform body and metering blocks and move on would be my suggestion.
 
I looked closer at the carb last night. The base is a 4779-2 as are both metering blocks. It's a 4-corner idle carb with the secondary power valve blocked off. Jets are 73 (pri) and 78s (sec). Squirters are HUGE. I believe they've been drilled out because the numbers have been filed off. Easy enough to fix... The air bleeds ARE the stock sizes. I spoke with Holley tech yesterday and got the stock specs. Idle air bleeds are stock .070 and and the inner ones are stock .031". I'm just gonna rebuild this and see how it runs. The throttle shafts are nice and tight and it seems to be in good shape. Worst comes to worst, I'll sell it and get a new 650dp and I'm only out the $50 for the kit.

And I totally see what you're saying. I spoke with Brian again yesterday. He said if the air bleeds have been drilled, I'm better off starting with a new carb. But since they are stock size, i'll see how it runs. I just wanna get this Eddy carb off my car. Never did like those carbs. Anyone in the market for a newish 600 eddy??? haha!
 
Are there any air holes in the butterfly's? For an 8 second car to be able to idle without some sort of band aid with this carb is amazing. Its not uncommon to enlarge the PVCR's behind the one powervalve, and to go with more emulsion holes in the carb metering blocks. The Proform body is what, about $100? That would be a good start before you put any more money besides a kit (which you'll use anyway) into that old carb. It may have radical pump cams and larger pumps too. I had an 850 off a big block "drag" car, got it in a deal and I started trying to detune it back to a 451 street carb. Well, same thing: things were drilled out, radiused, cut off, blended, thinned, vented, etc. The Carb shop (well known Holley gang) looked at it for about 10 seconds and gave it right back to me saying it was pretty much gone as a street carb, and even a race carb with all the hacks that were done with it. If you can do the machine work yourself, drilling and tapping for stock screw in bleeds (if it needs these) and emulsion holes, and replacing shooters and pump cams an diaphragms (~$18 a piece nowadays!) go for it, but that Proform is a great piece to start fresh with and it has all the proven legit hop ups already done to it. You may end up with a good baseplate (sans butterfly valves) and bowls..That is all I could salvage from that race carb. Good luck.
 
The butterflys have been drilled. How can I tell if the PVCRs have been modified??? How can I tell if there are more emulsion holes in the primary metering block? Home many are there supposed to be?
 
The car this was one was a Chevy 355ci N/A front engine dragster that weighed nothing. That's why it snuck into the 8's.
 
Not trying to sound like a "smart a**", but with all your questions regarding the basic workings of a carb and the fact you have a carb of unknown modifications,I believe you'd be way ahead of the game picking up a "box stock" carb and starting there.
By the time you know how some of these modifications will effect your engine it may be to late.Just my thoughts on it.
 
You can remove them. Thread the holes and install any size . They are available at any speed shop. I did it on a 500 2bbl for my Omni
 
68sedan said:
Not trying to sound like a "smart a**", but with all your questions regarding the basic workings of a carb and the fact you have a carb of unknown modifications,I believe you'd be way ahead of the game picking up a "box stock" carb and starting there.
By the time you know how some of these modifications will effect your engine it may be to late.Just my thoughts on it.
Click to expand...

I understand what you're saying and will probably end up going with a stock holley, but for now, what the harm in throwing a $50 kit on it and trying it out? If it works, great, if not, I'm out $50 and will have learned a lot.

So far, from what they Holley tech has told me, the carb looks to be in great shape. I don't believe much has been modified, with the exception of the 4-corner idle, the squirter size, and the butterfly valves.
 
removing Drilling and tapping for the threaded air bleeds[. I run a 500 2bbl on my omni and had to do extensive mods to the carb. QUOTE=mopowers;1969803291]What are you referring to?[/QUOTE]
 

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Start off a little fat put .76 jets primary side & .78's in secondary side , 0.025 in. Squirters in ,put a 4.5 power valve back in primary side & leave the secondary side blocked off -always have to run 2# high in jets to make up for the blocked off power valve. Don't worry about the butterflys have holes drilled that was trick to make them idle with a big cam and no vacuum. I would put 30 cc pumps back on both sides don't think you need 50cc ones- Run it You will be fine
 
Thanks for the input guys. I just figure why not run it and see what happens? What's the worst that can happen? I learn a little and end up buy a new carb? big deal right? Who knows, it may purr like a kitten.
 
If it were me. I'd put it back to box stock settings, jetting, PV, pump cams and squirters as a baseline. If you know your idle/cruise vacuum, you can make a better selection on a PV than what they come with. Probably not a big deal either way.

I'd run what Brian suggested. Brian built a 360 for a friend of mine, put a OOTB 4779dp on it. Car runs really well with no tuning other than idle mix and idle speed adjustments. Got 20 MPG on the highway with a 2.90-3.00 rear gear and 2500 hughes converter. Not bad for a car that ran almost 105 mph at MATS, 71 Demon. The carb was a smidge rich, so there was more in it!

The throttle plate holes can be filled with JB weld/epoxy.

If you want to sell the 750DP you have, I'd be interested.

Good luck with it.
 
crackedback said:
If it were me. I'd put it back to box stock settings, jetting, PV, pump cams and squirters as a baseline. If you know your idle/cruise vacuum, you can make a better selection on a PV than what they come with. Probably not a big deal either way.

I'd run what Brian suggested. Brian built a 360 for a friend of mine, put a OOTB 4779dp on it. Car runs really well with no tuning other than idle mix and idle speed adjustments. Got 20 MPG on the highway with a 2.90-3.00 rear gear and 2500 hughes converter. Not bad for a car that ran almost 105 mph at MATS, 71 Demon. The carb was a smidge rich, so there was more in it!

The throttle plate holes can be filled with JB weld/epoxy.

If you want to sell the 750DP you have, I'd be interested.

Good luck with it.
Click to expand...

I'll keep that in mind. For now, I'm gonna wait for the kit and see what happen when I bolt it on.
 
I meant nothing by what I said,I love to learn too.Trial and error is how I got my education,it's was costly.It's just that a good holley kit around here is $100.00 or so,or more if you want a trick kit.And a modified main body can mean trouble without an O2 and reading plugs(or dyno time) to see what the fuel curve is doing.Lean is mean.I have friend that thought he was a carb guy and melted a 440 from not knowing.I just thought with what you were asking it would save time, money and headaches for you to just get different/new.
 
68sedan said:
I meant nothing by what I said,I love to learn too.Trial and error is how I got my education,it's was costly.It's just that a good holley kit around here is $100.00 or so,or more if you want a trick kit.And a modified main body can mean trouble without an O2 and reading plugs(or dyno time) to see what the fuel curve is doing.Lean is mean.I have friend that thought he was a carb guy and melted a 440 from not knowing.I just thought with what you were asking it would save time, money and headaches for you to just get different/new.
Click to expand...

Thanks. I just paid $60 for an AED kit. The main body doesn't appear to be modified (from what I've measured). The air bleeds are stock size. It's just been converted to a 4-corner idle, which is pretty easy. I just need to rebuild it and swap jets, power valves, and squirters (which I have some of) and see what happens. Like you, this is how I learn. I enjoy doing things the hard way sometimes. I have a 66 that I learned to weld on, build a Dana 60 for, and so forth. All this was foreign to me at first, but I'm gettin there.
 
Cool...

Jump in with both feet. There's so much "black magic" sold about the difficulty of doing some car related things, auto trans as an example, that most get frightened.

Take it apart slowly, watch out for things you may not expect, squirter needles for one and lay the stuff out neatly like an exploded view if doing it for the first time. It will be easy. :thumbup:
 
crackedback said:
Cool...

Jump in with both feet. There's so much "black magic" sold about the difficulty of doing some car related things, auto trans as an example, that most get frightened.

Take it apart slowly, watch out for things you may not expect, squirter needles for one and lay the stuff out neatly like an exploded view if doing it for the first time. It will be easy. :thumbup:
Click to expand...

Thanks for the encouragement. I've actually already had it apart. I was amazed easily it came apart, how clean it was and how easily and free everything moved. That's really why I figured rebuilding would be a good idea. If I decide to go with a 650dp, I may just sell this carb. One thing I did notice was the bowls have the older style ball bearing type valve at the accelerator pump instead of the newer style. They moved freely and seemed to seal well. So we'll see once I get everything together with the new parts. Thanks again. I'm sure I'll have more questions as I get into it more.
 
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