Technical Flathead Dual Carb Questions

So, trying to figure out how to block off the idle mixture circuit. Seems if you turn the idle mixture screws in all the way, you will block off the main idle circuit and not the off-idle or transfer holes which are above the throttle plate and idle circuit holes (see diagram below). I guess you could also add some solder to the hole in the idle tube to block the idle circuit as well. Not sure if that’s a good idea considering the solder could come loose and ****** up other circuits or even somehow get into the intake.
Not sure how important it would be to have the transfer holes/circuit functioning on a progressive linkage setup considering the second carb would only kick in around the 65% full throttle position of the main carb. I’m guessing that by turning the idle mixture adjustment screws in all the way, the idle circuit is effectively blocked off, but the idle transfer circuit/p***ages would still be open. Soldering shut the idle tube would I ***ume block off both circuits. I’m surprised I can’t find more info on this subject on the interweebs. Going to strip down the remaining carbs today and tomorrow, and check to see how well the throttle plates seal against the Venturi body. If there isn’t a good seal, I’ll then probably bit the bottle and order the new secondary carb base that is guaranteed to seal.

Idle tube that could be soldered shut to block off both? circuits.

 

Full diagram.



Link to article with above diagram.

https://mikescarbtechnical.notion.site/Idle-Circuit-Holley-94-2100-1981c97f2e2a80e5a2c7e0bef19e97f3

 

Straight linkage and save yourself a headache and find some 97s. You will be better off. Ive tried progressive linkage with 94s and straight linkage with 94s. Blocked off power valves, differnt sized power valves. Finally found some 97s and its a world of difference from setup to driving.

 

Interesting. I’ll give this a try first. I’m trying to be budget minded, and would love some 97s, but the cost is typically $$$. If I can get a good seal on the throttle plates with any of the 94s I have, then that’s the direction I’ll go. I need a rebuild kit, a couple of extended length throttle shafts, and some throttle shaft arms, and I should be good to go for the most part, although I’ll be ordering some other stuff.
One carb base is practically new after bead blasting a few years back. There is no play in the throttle shaft, but plates need a good cleaning. One of the other bases is pretty crusty, and shaft is seized. The other 94 is working as it should. Nothing seized. I won’t go into detail in any rebuilds in this thread, but might create another thread of the rebuild. I’ll likely rebuild all three of my extra carbs.

 

Can see light past both plates where the shaft p***es through on the one non-seized carb. Got the other bases soaking in vinegar, and the seized base now has full movement on the the throttle shaft. Haven’t tested it yet for sealing, but came across this HAMB thread on lapping the throttle plates, but not much help in the “how to” dept. Seems thicker throttle plates are required to seal 100%, so a new base specifically built for a secondary carb used in a progressive linkage setup migt be the only way.

https://www.jalopyjournal.com/forum/threads/throttle-plate-lapping-compound.953538/

 

Looking at my current single carb stk intake and fuel pump, I started wondering how the secondary carb was going to fit. Decided to mock up a carb and a spare full pump/vent ***y on the Edmunds intake just to check. It looks like the second carb will barely clear the pump. I see they rotated the mounting studs on the intake for the pump/vent ***y. Ahhh…

 

Soaked a bunch of parts in vinegar yesterday and today. This one base seals perfectly Even though it’s still crusty a bit. Think I’ll just order new throttle plates with an extended shaft. No play on this shaft.

 

After even more head scratching, got the list of parts almost done. Will go with the Edmunds air cleaners to match the Edmunds intake if I can confirm they will clear each other. My carb centres are about 5”, but not sure on the max dia. of the Edmunds filters. Going to be about $500 for everything for the dual carb setup and rebuild of one carb, and this is on the cheap with no new secondary base, no fancy SS fuel lines, and no ready-made linkages. The Edmunds cleaners are good chunk though, plus an Edmunds choke brkt. Looking good is not cheap…lol!

 

Great vid on comparison of Stromberg 97 vs Holley 94. He’s got progressive linkage with a 3 x 2 setup on his Y block using Holley 94s with the PV blocked off on the outer carbs.

 

This works really good for sealing the blades, https://pontiactripower.com/collections/1965-tripower/products/throttleblade-sealer-dag

 

For some weird reason, I couldn’t get through to Vintage Speed yesterday. Tried 3 times, and each time I could hear them, but they couldn’t hear me. Got through this morning, but I’m on the road so just asked some questions. He recommended the following based on less than 2,000’ elevation, and having a mild cam or more:

Primary Carb:

#51 Jets
5.5 PV

Secondary Carb:

#48 Jets
Plugged PV

Will order everything tomorrow.

 

Had some delays due to other priorities, but finally got around to ordering the stuff this morning. They’re overwhelmed and behind, so not sure when it will ship/arrive but seems it might not be before Christmas. I found this vid, which was really interesting because I had many fuel leaks just before starting it up for the first time a couple months back. It’s weird, because this fitting is not in their catalogue, but I did order it after speaking with them.



He even sells the fitting on eBay! lol!

 

Holley 94 cores are very cheap. You should not have to pay more than $20 each. My advice is to find ones with better bases. Those seem to be in really rough shape.

 

Bases will clean up fine after bead blasting. The one I’m using now on the engine was in even worse shape IIRC. I think I have 4 spare carbs right now. Paid $20 or $25 for one at Hershey in Oct, and CAN$50 for one locally afterwards. Also, have one off of my second flathead plus another from when I rebuilt first one a few years ago. Getting new jets for both, new extended throttle shafts for both, new PVs for both (secondary will have PV plug), new hex head idle screws for both, and new idle springs for both, plus new throttle plates for the secondary, so essentially all new parts for the base(s).

 

Started a thread on the Barn about rebuilding the secondary carb for those intetested.

https://www.fordbarn.com/forum/showthread.php?p=2431454#post2431454

 

As I was finishing up the carb rebuild and tweaking things on my intake, I noticed the Edmunds intake only has 16 mounting holes vs the stk 20. Was a bit surprised to not notice that difference until now. Are there different gaskets for these intakes and what do folks do with the unused threaded holes in the block?

 

Pic of an Edmunds intake taken off of eBay. Same as mine.

 

Stk Ford aluminum intake.

 

The Barney Navarro high 2 carb manifold is supose to be the best performing / flowing manifold . However if you have the one above , run it and have fun . JW

 

I love the Navarro stuff, but way beyond my pay grade. lol! I would also love a Thickstun high-rise, or Eddie Meyer high-rise. Maybe one day.

 

As I was futzing around with replacing the br*** vacuum fitting on my intake, I was curious to know if the 1/4 NPT hole between the carb bases was a DIY addition or factory one.
So, going back to the one I found on eBay, it has a vacuum fitting in the same location. Therefore, I’m going to ***ume that is a factory feature or at a minimum, there were some instructions to drill the hole in that location for a vacuum port.

 

Just had this pop up in my feed. Navarro heads and Navarro dual carb intake. Intake similar to mine, and he’s running straight linkage. Not sure why he’s not running the stk fuel pump, and it seems an intake bolt is missing just under the first carb. Interesting…

https://www.facebook.com/share/r/1B1eAhT3sx/?mibextid=wwXIfr

 

Just ordered this off of eBay after checking out this post on the Barn. It reminded me that I had looked at purchasing one of these “uni-sync” airflow meters a while back, but then read the reviews which were generally not good. So, following the advice from @floyd in the thread, I found this vintage one. Might need some work, but at CAN$40 delivered to Ogdensburg, NY, it’s only slightly more than half of some Chineseium version on Amazon.

https://www.fordbarn.com/forum/showthread.php?t=321411

https://www.amazon.ca/dp/B073RPZKBX/?tag=atomicindus04-20

 

some helpful information here possibly.
lots of reading, - may or may not be helpful……..

https://www.jalopyjournal.com/forum/threads/links-to-holley-94-technical-info.286574/

.

 

Thanks! Can’t recall if I have ever come across that thread. Lots of broken links, but still lots of good ones. Information overload for sure, and likely some misinformation. lol!
An engine is essentially an air pump, and ***uming a single Holley could deliver all the air the flathead could need (***uming relatively stk setup like mine), adding a second carb will reduce the amount of air going through both carbs. Would it be an even 50/50 who knows, but reducing airflow would suggest (at least to me), one would need to increase jet size. The same principle applies to the PV, but in an opposite sense, meaning there would be a reduced vacuum signal (reading) with the addition of a second carb, hence a PV with a lower rating. All this ***umes the carbs are identical, and operate the same in terms of throttle plate position (e.g. straight linkage). Progressive linkage is another story all together and I can picture why folks might not recommend it or like it. First is the concept of different types of intakes as it relates to the placement of carbs, second would be ensuring the throttle plates on the secondary seal almost perfectly, and thirdly, would be blocking off the PV and idle mixture circuit (as far as I can make sense if it).
Either way, I will try my luck with both and see which operates the best for me. I plan to make some vids on the subject, so hopefully my findings can help others navigate this cluster of info with some hands on real world results.

 

I bought a new Uni-sync and used it for a while as bought. I pulled it apart and found casting flash in most of the ports and the holes didn't align very good. After a quick clean up with a drill bit and some vacuum grease on the joints, it works 10 times better. Before it had to have the adjuster valve about 90% closed to get the float up mid way, now it's more like 60% closed. Before the tool was throwing off the idle speed due to being choked down.

 

Speaking of Sync, The best and least expensive carb sync tool is a piece of fuel hose about a foot and a half long. Put one end in your ear and the other end at the carb opening and listen. When they are producing the exact same sound, they're in sync. So listen up and you'll be synced

 

That manifold looks similar to the one I'm using on the 8BA in my '50 Ford. There are a couple of bolt holes not used on that one as well (no holes in block) I suspect the manifold is drilled to accept more than 1 block configuration. I run straight linkage and it performs very well.