Multiple carb question

[oj]

I am interested in your opinions on how best to do the front and rear carbs of a 3 carb intake.  Should i plug the entire idle circuit or just run the idle mixture screw in tight?  Do i richen the main jet to compensate for the fuel that the idle circuit provided?
These are 3 holley 1904 1 barrell carbs going on a 6 cylinder.
Any other thoughts?
Thanks, oj

[wayne petty]

first.. did you see this on the 1904...

http://www.oldcarmanualproject.com/manuals/Carbs/Holley/H1904-IHC-1953/MCarbHollIHC53E322B/MCarbHoll_IHC_53B.html

page 7 describes the idle circuit

http://www.oldcarmanualproject.com/manuals/Carbs/Holley/H1904-IHC-1953/MCarbHollIHC53E322B/MCarbHoll_IHC_53B7.html


At the idle and low speeds, the velocity of the air flowing through the carburetor is reduced and the vacuum created in the venturi will not be strong enough to operate the main metering system. Because of the restriction of the air flow through the carburetor due to the nearly closed throttle plate, intake manifold vacuum will be high. This high manifold vacuum provides a pressure differential which is used to operate the idle system.   At the idle, fuel flows through the main jet into the bottom of the main well. The high manifold vacuum acting on this fuel through the idle system passages draws the fuel from the main well through a short horizontal passage into the idle well.

A calibrated restriction in the lower portion of the idle well meters the flow of fuel entering the idle system. The fuel passes out the top of the idle well and into the idle system passages in the main body. A metered flow of air from the idle air bleed is admitted to the fuel as it enters the idle passage in the main body. The idle air bleed also serves to vent the idle system to prevent any siphoning effect at higher speeds or when the engine is stopped. This mixture of fuel and air continues down, flowing through the idle restriction and, passing the two idle transfer holes in the throttle body, is discharged through the idle discharge hole into the strong manifold vacuum existing below the throttle plate. The two idle transfer holes act as additional air bleeds at the idle. An idle adjusting needle, which seats in the idle discharge hole, controls the discharge of fuel at the idle and provides a means for adjusting the idle mixture of the engine. Turning the idle adjusting needle in moves the pointed tip of the needle closer to its seat, restricting the fuel flow out of the idle discharge hole. This results in a leaner idle mixture. Conversely, turning the needle out allows more fuel to flow out the idle discharge hole to provide a richer idle mixture. During off-idle operation, which occurs when the throttle plate is moved open slightly past the two idle transfer holes, each hole begins discharging fuel as it is exposed to manifold vacuum. As the throttle plate is opened still wider and engine speed increases, the velocity of the air flow through the carburetor is also increased. This creates a vacuum in the venturi strong enough to bring the main metering system into operation. The flow from the idle system tapers off as the main metering system begins discharging fuel. The two systems are engineered to provide a smooth, even transition from idle to cruising speeds

i would think that the idle transition system is going to need to be fine tuned.. so when the secondary carbs start to open and are drawing fuel from the idle transition slot.. it won't go too rich or too lean..

i would also want to think about checking the air leak past the end carb throttle blades..  if you want to drive it mostly on the center carb.. as any air leaks out at the ends carbs might lean the fuel mixture from the center carb out for the cylinders at both ends..

somebody familiar with the air leaks around the throttle plates of the tripower set ups might know if they have ever tested it..




i am not an expert in multicarb installations..  i just understand carb metering ..

do you have an infrared thermometer.. so you can look at the temps of the sections of the exhaust manifolds... this one goes to 1100F where most of the others stop at around 750F

http://www.harborfreight.com/flex-shaft-infrared-thermometer-94233.html

this way you would reach around and examine the temps of the exhaust manifold to see what the exhaust temps are..   not as good at a bunch of pyrometers, a thermal camera or oxygen sensors..


say... have any of you six cylinder ford guys ever seen the exhaust manifold on an 80 or 81 fairmont 200?? with the 4 inch  4 bolt outlet??? where a can type preconverter is bolted up..
cannot find a direct picture of the manifold. but look at where the preconverter bolts up in this image..

http://www.walkerexhaust.com/images/catalog/coupons/10868.gif

probably too big to properly scavange the exhaust properly without the honeycomb monolith inside.

[oj]

Thanks Wayne, that is about as good a description of the idle circuit as i have read.  I assume it came from International harvester?  Thier manuals are incredibly informative and i just love the IH spec'd holley 2bbl carbs - they are just the best carbs ever.
These holley 1904's are different for sure and i am curious about how well they'll act.  These things are like the transition carbs from like the 94 series where the passges etc are machined internal to thye main body and the 4150/60 that are modular in design - the 1904 has like an internal metering block that is removable and is the predecessor to the 'modern' holleys.
I am still working on the individual pieces: linkages, throttle stops, base plates etc and when i get this thing together i'll post a pic of it.

[wayne petty]

you will also want to check this site out..

https://buy.walkerproducts.com/carburetor/components/holley/holley-1bbl-1904-1-carburetor-components.html

they have the plastic bellcranks or pump levers..  and a bunch of other stuff not available elseware...

you also might want to visit a snap on tool truck or the site..

look for the welding tip drill set ..  and or the tiny drill bit set .. i have the welding tip drills in the aluminum tool with the chuck on one end.. comes in very handy when modifying and verifying tiny passages in carbs..

Set, Micro Utility Drill
Stock#: YA246A

    $22.20
Description:
Applications include fuel injectors, fuel lines, welding and soldering torch tips, shower heads, water jets, electronics and hobbies. Knurled surface at chuck end of pin vise provides a sure gripping surface. Long 1.88" (47.6mm) drill length. Plastic coated handle for comfort. Includes pin vise and twelve precision HSS twist drills in storage case: #52 (.0635), #54 (.055), #56 (.0465), #58 (.042), #60 (.040), #62 (.038), #64 (.036), #66 (.033), #68 (.031), #70 (.028), #72 (.025) and #74 (.0225).


lastly.. there are 4 sections of this 1904 tear down and reassembly..

the links are at the bottom of the page..
http://www.binderplanet.com/forums/showwiki.php?title=Holley+1904+Carburetor+Rebuild+Disassembly+Part+1

hope i don't swamp you in info...

i will lay off now..

[oj]

No, you didn't swamp me Wayne.  Looks like we share similiar interests, have you been to IH North? Michael Mayben? he is about as slick with carbs as anybody i ever saw.
I do away with the plastic arm, you relocate the stud down to the next boss, drill and tap the hole, and then use a steel arm.

[enjenjo]

On a three single setup, it's usual to fill the idle circuits on the end carbs. You can inject epoxy with a syringe to fill them. You also want the throttle plates on the end carbs to seal as tightly as possible at idle. Keep the accelerator pumps functional, you may have to limit the shot when tuning. Run the end carbs progressive with the tip in at about 1/2 throttle.
As I recall, 4150 jets will fit, but are calibrated differently, so you will have to play around with them. Depending on your applicaion, and the tune, you may want to eliminate the power valves on the end carbs, and enrich the main jets on them two to three sizes.