Carb question - waking up old 700 DP

[Falcon67]

Maybe get a reading from our local carb guys on this idea.  Background - the dragster runs good, sorting out all the little stuff.  Making a bit over 500HP, shifting at 6800.  Brent says I'm not spinning it high enough yet LOL.   It's inconsistent between 60' and 330'.  Incremental is real good between 330' and 660'.  I feel like its a carb issue because it'll pick up and not change 60' enough to warrant the 330' increase.  I can also feel it "not pull just right" sometimes on the way to high gear.  Burnouts and staging RPM are consistent.  In the heat we expect maybe .02 variation in 60', but that doesn't explain a 330 going from 3.74 to 3.68 in the same lane 45 minuets apart.  330-660 is good - 3.68 i the middle means 5.68 on top.  3.74=5.74, etc.

Have a built up "750" using Quick fuel blocks, ProForm base and such.  It's a little fat but it is hot here.  Have no idea what's in the thing, I need to tear it down and get a measure on the details.  Pretty sure I ran the blocks as delivered.  The main thing is that I'm not trusting it's anywhere close to right.

Option 1 - have a local guy that has built a methanol carb.  He has an excellent rep and several cars run his stuff and you can set your watch by the ETs.  No oil milking, no issues.  However, only have one TnT left before football season and I'm loathe to turn the fuel apple cart over on one single test.  Have to engineer an air bleed setup, get top lube and get some test fuel - everything else should be in place to run alcohol.  Plenty of pump, plenty of lines, carb in the wrapper ready to mount.

Option 2 - have this nice old 4778 700DP.  Date code is 2nd week May, 1972.  Near as I can tell it's original.  From looking at the specs, I can probably put 4776 blocks on it (have plenty) and jet it to 4778-2 up specs.  It has some interesting looking straight leg stepped boosters.  So that's really the Q - would it worth while to tinker with the 700 and try that since I can't really trust the home brew frakencarb on this motor.  I have a nice 650DP on the door car that runs very consistent so that's why I pulled the 700 out of the box and started looking at it.  Interestingly, out of all the carb piles I have here there is not one stocker 4779. 

Opinions welcome.

[Drew Pojedinec]

Those funky straight legs are called bell boosters.
Ford CJ carb had them on the primary. They actually work
Really well.

The 4776 blocks will need some drill bit attention, if I recall
The idle feed is a good bit smaller.

[Falcon67]

I'll dig out the small number drills and take a look.  Idle isn't a big concern except for driving back to the pit and up to the line, rest of the time it's wide open.

[Drew Pojedinec]

The rest should be the same.
Only difference other than ifr is when you get to the
4779 with downlegs there will either be a .026 killbleed in the angle channel or a raised booster feed.

[Falcon67]

One thing that stood out from the list numbers - there was a substantial change in rear jetting between the original and the first dash numbers.  66/71 then -1 went to 66/76.  Then at -3 they went 69/78.  A 4777-2 set of blocks listed as 67/76 should drop right in more or less.  Now to see if I really have some like I think I do, in that big ratty box marked "misc Holley parts".   

[Falcon67]

Interesting- 4778 IFR .055, 4776-2 .032.  Large difference. Not sure what to make of that.

[Falcon67]

Oops, I need to check the idle air bleeds also.  Forgot there is likely some sort of ratio there.

[Drew Pojedinec]

Where are you getting that number?

[Falcon67]

The idle feed restriction in the metering block.  Drill bit measure, don't currently have a set of check pins.

[Drew Pojedinec]

I mean what location. Early carbs often have the ifr under the cup plug in the idle well.
The ifr on a 4778 is not .055

[Falcon67]

Block looks like this one.  it may not be the real 4778 block.  The blocks are not stamped with the list number, like most carbs.  I'll get a full pic of both blocks when I get in tonight. 

[machoneman]

Late here but....stick to the gas carby for now. Maybe a late/post-season shift to alky. 

[Falcon67]

Pic attached of primary 4778 block.  That's a .054 diameter bit sticking out of the IFR.  What details I gathered last night -

4777-2
Primary IFR - .029
Secondary IFR - .039
Idle bleed - .072
High bleed - .054

4778
Primary IFR - .054
Secondary IFR - .054
Idle bleed - .020
High bleed - .028

[fordman460]

Make sure there isn't a smaller hole down inside that .054! Got caught with that one once. Can't tell from here how far the bit is in the hole.