“2 Corner” Idle Mixture With E85?

[the rain maker]

I have a couple old carburetors I am messing around with and converting to E85. One is a 4777 ”650” and the other is a 4778 “700” Holley. I had planned on using 2 primary metering blocks and converting them to a “4 corner” idle mixture but the 650 main body does not have provisions. Has anyone converted over to E85 using the 2 corner idle adjustment? If so, what needed to be done? And what ebleeds, MAB, & IAB were used in the secondary? I noticed the secondary blocks have more of a straight than angle cross exit. Any feedback is appreciated...

Here is the set up I’m going with for the 700, feel free to critique it if you like

Boosters .166
IAB .059
MAB .026
Cross .151
Main well #2 taper
PVCR .073 Front, blocked rear
IFR .040
Converting to 4 corner with 2 primary metering blocks
MJ 78/85

The 650 boosters are .161

Here’s a couple of pics of metering blocks and main body

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868A0EF5-C9E3-4227-86AE-2559AE9FBA6A.jpeg

BC2509C9-FE84-4A18-A12B-183B8B2A0B01.jpeg

54F431BE-E105-488C-8AE3-497B6EEAE6DF.jpeg

[the rain maker]

Well, I manned up and drilled the main body. Problem solved

[PRH]

FWIW.......The 4777 primary metering blocks have emulsion tubes pressed into the main wells, which can become a restriction when high fuel flow is needed.

[the rain maker]

Thanks PRH. I had an assortment of blocks but I did remove the tubes and used a pin taper in the main wells. I had a couple metering blocks with “hidden” IJ location. I’m not sure if those idle wells should be drilled or not...

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[Ks Fats]

For the past 30+ years I have always 4 cornered the idle on all carbs whether for personal use or customer. I did this because I was told that race engines "need" a four corner idle system. Now I'm beginning to question the rationale behind the modification, if one has a basic 350 platform with say 10.5 compression, hydraulic roller etc. is it a necessary change? I understand the distribution improvement but there are ways to achieve that without going to 4 idle feeds. I guess the real question is: What dictates the "need" for a four corner? I'm usually always working with n/a engines so blown applications aren't relevant. I'm doing a similar build (e-85 also) with a 650 h.p. main body but with a 1.750 base plate. Drilling the base plate (Holley not aftermarket) for idle outlets isn't a problem but is there a real need for it? This will be a spare parts build for a 604 spec.deal.(Planning to leave the straight leg boosters in @.159 for initial testing). Don't mean to highjack the thread but seeing the similarity in builds sparked the question.

[Lizardracing]

Probably somewhere in the area that long cams that need more air on from the primary throttle blades open so far the transfer slot become uncovered. You can open the secondaries to leak in some air and help that but a four corner adjustments sure give better tip in feel and a more linear fuel curve.

[Ks Fats]

Thanks for the reply Lizard; I understand what you are saying about the camshafts effect. When I do a four corner idle I usually end up with t-slot restrictors, depending on the length of the slot itself, to control that segment of delivery. When using the old style Holley b/p with the channel in it, a four corner delivery can be done that is still fed by the primary side IAB and IfR, if they were reasonably close from the factory it should only take minor tweaking if the fuel used is the same. The secondary side t-slot also has a bleed hole below the slot that can be varied in area to add to or detract from the fuel flow. I've always used four corner on methanol because of the volume issues but with e-85 the volume increase isn't near as great as with methanol. Ethanol (if memory serves me correctly) will have a lower Reynolds number through an orifice or channel than gasoline or methanol such that it would be possible to feed the four discharge ports more readily. We would still have the airbleed and feed orifice for the t-slot variables on the secondary side also. I've worked on carbs that had a restrictor in the idle feed down channel in the mainbody, when I questioned the original builder he said they were there because "when I got the t-slot right the idle was wrong" AND the carb had four corner idle (restrictors in all 4 downfeeds). Prompted me to question whether or not my thinking regarding throttle response and four corner feed was correct. I have three e-85 carbs with 4 corner idle feeds to compare with, probably best to just build this one and test. Thanks for the input

[jmarkaudio]

2 to 4 corner idle mod with pics.
https://www.tapatalk.com/groups/racingf ... -t364.html

[the rain maker]

Thanks jmark, I drilled the necessary holes in the baseplate.