new carbs

[fryedaddy]

i bought a new 850dp in 1984 and i used it on 2 different 390s and my new 433.it ran great all those years till i decided to replace it last summer.so i went out and bought a new 850dp,manual secondaries and manual choke.the problem is it is not as crisp as the old one.the old one even sounded better idling.is there anything i can do with this new 850 to get it to perform better,or should i get rid of it and go with something else,if so what would i want.the car has 4.11 gears and weighs less than 3000.i will buy something else if i need to,but i would also mod the new one too.the old dp is long gone so its not an option.

[Falcon67]

I personally am having carb issues - I'm usually pretty good with the things but lately they have all turned on me.  Anyway - every 850 I ever saw somebody use or worked with was "lazy".  The throttle bore and venturi sizes are - IMO - too close in size and have issues metering fuel unless it's a fairly big displacement.  The "950"s always seem to do better.  Depending on what you are doing, I would consider a 650 or 750.  The 650 DPs are good carbs, tune well and easily support over 500 HP.  Very crisp.  I have two here, one is the go-to carb for everything.  It ran on the 302, then went on the 393C in the dragster (same ET/MPH as the home brew 800 DP) and is not on the wifes Mustang racer (7.44 @ 90.5 MPH).  That's a $40 swap meet carb and you can't buy it from me for love nor money.  If you really want to keep that one, you might touch bases with someone like Patrick at Pro Systems. 

[RJP]

i bought a new 850dp in 1984 and i used it on 2 different 390s and my new 433.it ran great all those years till i decided to replace it last summer.so i went out and bought a new 850dp,manual secondaries and manual choke.the problem is it is not as crisp as the old one.the old one even sounded better idling.is there anything i can do with this new 850 to get it to perform better,or should i get rid of it and go with something else,if so what would i want.the car has 4.11 gears and weighs less than 3000.i will buy something else if i need to,but i would also mod the new one too.the old dp is long gone so its not an option.

Do you still have the old 850? If you do have that one rebuilt and use it. Older Holleys have more precise fuel metering which is why I prefer building and using the older Holleys rather than newer ones. Just make sure you address the warpage issues normally associated with these old cores.

[cjshaker]

I went through the same thing a couple years ago. Had an old 750 VS that performed very well for over 20 years, but I wanted a new carb for the engine I bought off of Blair for my '70 F350. Purchased a new Holley 750 (same carb I had) and it ran like crap and would hardly idle. I had it apart probably 5 times checking, adjusting and just generally fiddling with it, but never got it to perform worth a damn. I finally gave up and just rebuilt my old 750 and it ran great. I'm not a guru when it comes to emulsion tubes and some of the finer points of carbs, so I never figured out the issue. I've never had an issue getting a carb to run right, but I've always had older carbs. Lots of rumors about Holleys quality going down with all the buy-outs and whatnot, and I tend to believe it after that experience. Carbs are like wives and girlfriends, if you find one that treats you good, NEVER get rid of it

[fryedaddy]

old carb is gone as mentioned.the car is a street strip type setup.i need a carb for that purpose.when driven on the street i rarely go over 15-20 miles,so drive ability is not a concern.i just want it to perform when i hit the throttle and sound good at idle and wot.engines a 428,.030 over,10.7 speed pro pistons,bbm heads,rpm intake,comp cam hyd flat tappet .244 at ,050,msd dist,box and coil, hookers,arp studs rods,mains,heads. all i need to be happy is a good carb,all input is appreciated.

[Drew Pojedinec]

Universal carbs expect you to have a massive cam, so large restriction are used as the planned usage won't have high vac to pull on them.
As such it runs rich in most applications, which is safer for the manufacturer and sucky for the owner.

Many newer carbs like to over emulsify as well for some reason which makes initial booster operation shoddy.

If you find a carb you like, pin gauge it and record the calibration, it's easy enough to replicate later if need be on any other carb.
Here is a 750 4779 I have that runs freaking awesome:

List number         4779
Type            4150
Primary
Float            center hung brass
Booster            downleg
Pump nozzle         .031
Pump type and cam      30cc blue
Idle air bleed         .067
High speed bleed      .028
Metering block#         8543
Main Jet         70
Power valve         6.5
PVCR            .052
Emulsion         2 @ .028
Kill Bleed         .028 in angle channel
Idle Feed restriction      .033
Needle and seat         .110
Venturi size         1.370
Throttle plate size      1.680

Secondary
Mechanical or Vacuum?      MS
Spring color         na
Diapghram length      na
Float            center plastic
Booster            downleg
Pump Nozzle         .031
Pump type and cam      30cc blue      
Idle air bleed         .026
High speed bleed      .025
Metering block/plate#      6501
Idle Feed Restriction      .031
Jet size         80
Needle and seat         .110
Emulsion         2 @ .028         
Killbleed         none, raised feed
No secondary power valve
Notes:
Changed to stepped downleg .152

[Falcon67]

Don't buy a Holley, or buy a Holley 950 Ultra.  Or Pro Systems, or Quick Fuel. 

[cjshaker]

Don't buy a Holley, or buy a Holley 950 Ultra.  Or Pro Systems, or Quick Fuel.

So if wanting to buy a new carb, what does that leave? In other words, what places would anybody recommend for carb work beyond basic tuning and calibration? The only other place I can think of is AED.

[fryedaddy]

 Drew,thanks for the detailed info.if i decide to go with what i have,i may try some of your info on it.are AED carbs good out of the box.i dont mind paying a little extra if im happy with what im buying.also i have low vac and would this affect carb choice.

[Drew Pojedinec]

AED is awesome.

Dunno if you can see this, but this is that 4779 on my stockish 390 pickup truck engine:
https://www.facebook.com/AirFuelSParkTech/videos/186653008740105/

Just sold that carb about 5 minutes ago   Kinda wanted to keep it around, but gotta make more room for new builds.

[Nightmist66]

Don't buy a Holley, or buy a Holley 950 Ultra.  Or Pro Systems, or Quick Fuel.

So if wanting to buy a new carb, what does that leave? In other words, what places would anybody recommend for carb work beyond basic tuning and calibration? The only other place I can think of is AED.

ACFI, AED, Baker, BLP, Braswell, BRE, CFM, C&S, DaVinci, DeVane, Chuck Nuytten

I'm sure I missed a couple.

[cammerfe]

Step outside your comfort zone. Go to throttle-body EFI. You'll be so pleased by the instant reaction, the quick start and off-idle drivability you'll wish you'd gone to EFI thirty years ago. My own experience has been with the Holley systems, but I haven't done one recently. Some of the other new brands may be as good or even better.

KS

[My427stang]

With a double pumper, hard to beat AED and a custom build.  They really do a nice job and verify everything on a wet flow tester.  Not sure where you are, but a phone call and box sent to Richmond can get you some nice tuning, especially if they get rid of the later style IFR

A buddy used them for a pair of 390GT carbs he had on the shelf, and they did great too, but they don't sell any vac secs that I know of.  They tend to focus on double pumpers like yours. 

Drew could certainly make yours do better too. 

[Falcon67]

Don't buy a Holley, or buy a Holley 950 Ultra.  Or Pro Systems, or Quick Fuel.

So if wanting to buy a new carb, what does that leave? In other words, what places would anybody recommend for carb work beyond basic tuning and calibration? The only other place I can think of is AED.

ACFI, AED, Baker, BLP, Braswell, BRE, CFM, C&S, DaVinci, DeVane, Chuck Nuytten

I'm sure I missed a couple.

Throw APD in there too, just close to $1000. 

[machoneman]

Well, unless it's for a WOT race engine, I've read many have the same 'lazy' issue with 850 DP's used on the street as other here have also noted. Bet a stock 750 DP'er would be noticeably better as would a worked one or a worked 950 (750 based) frrm one of the shops mentioned. Must have someting to do with the bowl/venturi area and even the air bleed sizes demanded by thta bowl's flow. BTW, heard the same long ago with the old Holley 3-barrel but methinks that was an issue with pure overcarbing a too small, too mild engine.