Bomb Shell venturis

[aumick10]

I am trying to understand how the bombshell venturi's work.
If the emulsion tube extends into the center section of the venturi for low speed operation, when in high speed operation, how does the same emulsion tube supply enough fuel to keep the correct fuel ratio.
Does the extra air going around the outside of the bombshell venturi not have a direct influence on the amount of fuel drawn through the emulsion tube, only the increased air flow through the inside of the bombshell affect the fuel ratio.
Am i missing something here.
Thanks for anything to help me understand.
Cheers,
Mick

[RichO]

I've always heard in called bombsite because it looks like one and it's purpose is to get a more even and forceful and complete mix of fuel and air. I could be wrong.

[T. Cotten]

I don't understand the "bomb-sight" either, Mick!

(But then I don't honestly understand lots about the DLX design, copied by Linkert.)

How did it work? Apparently not very well.

One guess is that the secondary venturi was meant to draw from the nozzle at lower RPM, without obstructing the flow at higher RPM,... much.
Even more enigmatic is the "drool pit" in the bore beneath the venturi, with an opening to atmosphere through the vented bowl. If that is not a vacuum leak, what is it?
I'm seriously dumbfounded that the M53 series ran at all.

....Cotten
PS: I previously asked if anyone had pertinent literature for these models, but only got crickets.

[kitabel]

W/r/t "draw from the nozzle at lower RPM, without obstructing the flow at higher RPM,... much"
Yes, it produces higher vacuum at the nozzle tip at lower engine speed, at the expense of reducing the total CFM flow. It doesn't produce more power, it makes a small engine happier with a big carburetor. If you don't need it, don't use it.
Best use: 45" engine, large throttle disc (K, WR).
When the engine size went 20% higher (KH) it was discontinued as unnecessary. The plain 1-5/16" (74) larger venturi was also favored in the KR for the longest tracks: peak power more important than response and range.
The correct placement of the booster is with its smallest diameter slightly ahead of the nozzle tip, with the booster's discharge end located at the main venturi's smallest diameter. It's too long to retro-fit into a "normal" carburetor. Eric's Http://beautyofspeed.com has a good diagram.
The DaVinci etc. leaves the stock big venturi in place and puts the booster inside it (the nozzle extends through both), which doesn't have the intended effect.
I've adopted a booster from a 4150 Holley, but no back-to-back tests. It feels better, but how valuable? IDK.

[T. Cotten]

Can't find the diagram, Kitabel!

(Met Eric at D-port once though.)

Can you post a specific url?

Thanks!

.....Cotten

[kitabel]

Can't find it, here's a copy I downloaded years ago

Bombsight_specs-inches-small.jpg

[T. Cotten]

Great, Kitabel!

For the rest of us, here's a pic of one.

The 'drool pit' was much more exposed than with the later conventional venturi.

It boggles me.

...Cotten

[kitabel]

Here's the DaVinci installed, note the nozzle tip goes in the original position (close to the main venturi smallest point) and through the booster.

unnamed.jpg

[kitabel]

The booster concept is one way that Rochester made the QuadraJet work at low throttle openings on engines as small as 230" L6: triple venturis (main + 2 boosters, one inside the other).

[T. Cotten]

Here's the DaVinci installed, note the nozzle tip goes in the original position (close to the main venturi smallest point) and through the booster.

[ATTACH=CONFIG]29236[/ATTACH]

It confuses me, Kitabel...

(Probably because I can't even identify the modern carburetor!)

The DLX/Linkert nozzle spigot 'tip' extended to just shy of the center axis of the bore.

Is it just camera angle that makes yours seem so low in the bore, and no exposed spigot at all?

....Cotten

[kitabel]

Looks like it stops flush with the floor of the booster, surprising. I thought the air stream across the tip opening contributed to the suction, but...?
In addition, the Linkert nozzle tip itself (at least the part protruding above the venturi floor) can be modified to:
1. change the timing (make the main system "come on" earlier or later) by raising or lowering the whole nozzle or just the tip
2. increase the vacuum signal by removing part of the upper section in different shapes (like Mikuni and Amal)
The side drafts have a disadvantage in that the annular venturi (discharge holes drilled inside the booster ID all around instead of a single tip entry) popular with Holley won't work when turned 90 degrees.

[T. Cotten]

Looks like it stops flush with the floor of the booster, surprising. I thought the air stream across the tip opening contributed to the suction, but...?
In addition, the Linkert nozzle tip itself (at least the part protruding above the venturi floor) can be modified to:
1. change the timing (make the main system "come on" earlier or later) by raising or lowering the whole nozzle or just the tip
2. increase the vacuum signal by removing part of the upper section in different shapes (like Mikuni and Amal)
The side drafts have a disadvantage in that the annular venturi (discharge holes drilled inside the booster ID all around instead of a single tip entry) popular with Holley won't work when turned 90 degrees.

Ah sweet cheeses, Kitabel!

Can't we keep this simple?

Got one on the bench, Mick?

....Cotten

[aumick10]

Cotton, i don't have one on the bench. I will be building a 80" JD motor sometime, using the twin carb, JDXR cylinders from JD Jugs.
With high lift cam and valve rockers, it should flow more than a std motor.
I think each carb will be in the 1" bore range. My concern is with each carb feeding a single cylinder, the air velocity may be low off idle, giving a sluggish response.
This is the reason i was asking about the bombsight venturi.

I might be able to go to a 1 1/4" carb with a bombsite venturi, which should give me full airflow under power, and still have good throttle response just of idle.
Cheers,
Mick

[T. Cotten]

You have access to two M53s, Mick?

Or are you considering attempting the modern "hybrid" offering (on right in first attachment).

The 1" models of DLXs and Linkerts came in a wide range of bores to play with, or you could just cut your own as you please, of course.

I honestly have no experience with dual carbs, but I've got some Knuck heads for anyone who needs them!

....Cotten

[aumick10]

I have looked at a pair of M53's as an option.
Are these a 1" carb.
The cylinders have 1 1/4" flanges on them, so i may need something like the M35, with a modern bombsite venturi.