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Discussion Starter · #1 ·
I'm converting my 4777 to 4 corner idle but can't find a match on my thread guage for the mixture screw. Does anybody know?
 

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I've never seen the conversion done by tapping the existing metering block. I'm pretty sure you're going to need another rear metering block. Do a search. I'm pretty sure this has been discussed before on Ford Muscle. MJ
 

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Holley is notorious for using odd-ball thread pitch and size on their stuff. Probably the only place you'll find a tap that size is through Holley.
 

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Discussion Starter · #6 ·
Thanks fella's
holley must be up to some no good, still haven't had any luck with that thread type. I've got a couple of good, detailed ref's for the conversion and its quite simple. The only thing that I cant find is you know what. I've got a few spare primary metering blocks which I could use with a power valve block off I guess. I'll be at it this weekend either way . Chris
 

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Ramo,

We did a 700 DP up with a 4 corner conversion. we simply swapped a primary metering block off of a 650 DP onto the secondary side of the 700 DP.

Are you sure that the metering block with no idle screw provisions will work once drilled for idle screws? I would be nervous about metering passages and air bleed passages not being completed.

Good luck with it,

Greg
 

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The thread is a 8-32 NF , be very careful drilling the blocks , if you go too deep you will go through the well and the screw will have nowhere to seat but a hole through the block that will leak all over, and not deep enough won't open the idle well enough to be decently adjustable, there is a website somewhere that covers this conversion and if I can find it I'll post it up for you,

<font size=-1>[ This Message was edited by: Fomoco8 on 10/11/06 9:18pm ]</font>
 

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Discussion Starter · #9 ·
Greg, that was plan B. It would appear to be the easier way. My carb is the 4777-4 and it seems to have most of the holes already drilled on the body. Two holes need to be drilled on the base of the main body to feed through to the throttle plates. And as far as I can see the secondary block has all the circuits but for the mixture screw facility already to go, right down to the brass idle feed restrictions. I'll give it a go and if it works out the next one will be easier.
fomoco thanks heaps for that thread size and the timely warnings. If you can post that website I'd be grateful.
 

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There is more to doing this conversion then already mentioned.... The Idle Air Bleeds on the secondary side will also need to be enlarged by a large amount. How much depends on the IFR installed in that metering block. Cureently they are probaly near 36, need to go to near 75.....
( what size carb do you have???)

You will also need to install plugs in idle feed circuit from the primary to the secondary and enlarge the idle discharge holes as someone else has already mentioned. These are all located in the throttle plate block.

May I ask how you came to the conclusion you need 4 corner idle? I do not see your engine application and specs... chances are you do not need it at all... and you will mess up a perfectly good carb in the process. This is a very difficult mod if you have not done it before.

If you insist....As Greg suggested, you should get a primary block from another carb. That will reduce the amount of trouble you are going to have....

Also, if the mod is done correctly and the carb works like it is supposed to with the mods... then tuning the carb to have the correct front / rear idle balance is another difficult issue you will have to deal with. The IFR ( Idle Feed Restrictor) must be correctly set for the proper balance, or you will be pulling fuel out the primary or secondary transfer discharge slots, when you don't want it to, causing lots of mini gas explosions in your exhaust system....very poor milage too....
 

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PS: Yes-odd ball screw sizes.... Did you folks know that the shooter screw ( the big one in between the ventuires) has only 2.5 turns of the thread going into the threaded part of the accelerator pump channel boss?

It is a long screw, but only 2.5 turns make it into the threaded area. Meaning, carefiull or you will strip it, and guess what... it is an odd-ball size thread, and there are no heli-coil replacements... meaning the carb is junk if you go too tight...

Don't ask me how I know...(painful laughs)

It seems though the hollow type aftermarket shooter screw makes more then 4 turns of contact into that boss..... It is a longer screw....

Wish I knew that too....( painful laugh)
 

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On 2006-10-12 02:26, ramo wrote:
Greg, that was plan B. It would appear to be the easier way. My carb is the 4777-4 and it seems to have most of the holes already drilled on the body. Two holes need to be drilled on the base of the main body to feed through to the throttle plates. And as far as I can see the secondary block has all the circuits but for the mixture screw facility already to go, right down to the brass idle feed restrictions. I'll give it a go and if it works out the next one will be easier.
fomoco thanks heaps for that thread size and the timely warnings. If you can post that website I'd be grateful.
That's good news. Be careful drilling the idle discharge hole in below the throttle blades. One false move there and POOF! Time for a pro-form main body...lol...

To avoid the front to back balance issues I epoxied shut the balance channels in the baseplate that connected the rear barrels to the front barrels idle system.

This allowed me to leave all the secondary air bleeds alone., and they woeked just fine with the primary block I put back there.

Regardless of your engine's build level, it never hurts to have more adjustability. 4-corner all the way, baby!

Greg
 

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Greg, did you ever get around to doing the modification for jet extensions on your secondaries? Or did you find you had a different issue then we all thought? I know you were messing around with the gas line sizes too....

Just want to know how that turned out, and what you did to clean up your off-line acceleration per your video.

Another thing I learned. The Holley Jet extensions where you have the jet at the end of the extension.....not really the best thing in the world.

Much better then not having them. But The type of extender where the jet is at the end of the extension is not as good as a cover over extender. Where the jet stays in the metering block and you put an extension cover over it.

Reason why.... The area behind the jet ( in the extension cavity) is a larger diameter then the actual jet itself. Meaning, for the initial moment of fuel flow starting into that circuit, it can be up to 5 - 10 jet sizes larger (staticly) then it should be, for a very small amount of time.

Think about it. The jet restricts overall fuel flow, when it is flowing, but when at rest, the larger then jet channel behind the jet is filled up. Then when the circuit starts to flow, it will be overly rich, untill the reserve is depleated, then you will have your standard fuel air that you initially set it too...

Motor on.....
 

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Not sure I agree with your jet extension theory, from a fluid mechanics standpoint, but I have never tried it either way....

The carb was launching just fine, but leaning out at the top end. I have a Mallory 250 fuel pump coming that should alleviate the top end lean condition.

Greg
 

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Leaning out at the top end might be caused by a wrong power valve closing at too low a vacuum - or too small a carb on the engine causing the vacuum to go above the rating of the power valve at the top end. It might be that you have accelerated to the point that your fuel bowls are dipping below their full state during your hardest acceleration and they haven't caught up yet. Thet you could test with a pressure gauge. If you had a vacuum gauge you could be sure of your vacuum as you cross the line too. Guessing at remedies or the problems causing the symptoms can be an expensive way to troubleshoot.

<font size=-1>[ This Message was edited by: PaulS1950 on 10/16/06 10:33am ]</font>
 

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Out of curiousity, how would the fuel bowl situation be solved?
 

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I know that the fuel pressure is dropping to 4 psi at the big end. Also, the car runs 3 mph faster (in the 1/8!) with the air cleaner on vs. off.

The primary PV is a 4.5" and I am running 84's up there. The rear pv is plugged and I was running 88's there. The carb came with two pv's and 78's all around.

I will slap in a 6.5" pv next time and see how it goes.

Greg
 

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If you take the vacuum reading(in gear) and divide that by 2, you will get the correct PV you need.
I'm switching from a 6.5 to a 8.5PV to see what that does for me because I think I'm leaning out on the topend too.
 

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My car has 8" of vac at 1000 rpm in gear. I discovered a blockage in the fuel line tonight while I was installing my 250 GPH fuel pump.

Seems like the -8AN line was about 80% blocked.

I am hopeful that this helps my fuel starvation issue.

Greg

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'71 Torino GT - 545 stroker, Edelbrock CJ heads w/ 11.8:1 compression, victor intake with 850 DP, Broader performance C6, Edge converter, 3.89 detroit locker

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<font size=-1>[ This Message was edited by: GregP on 10/17/06 12:51pm ]</font>
 
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