Carby identifcation

[macca]

If a m35 is jetted & the same venturi & other bits fitted the same as an m74b is it the same ???

[T. Cotten]

If a m35 is jetted & the same venturi & other bits fitted the same as an m74b is it the same ???

An M35 has no fixed jet, Macca,

All fuel was metered by the highspeed needle;
But if all things are in order, swapping out the venturi and/or nozzle should run, but with its own unique character.

Swapping from a 12° o 9° throttle disc raises the question of where it lands between the idle bleeds..

I won't guess how it will run, but I'm pretty sure it will run.

..Cotten

[dukekleman]

Macca,

The quick and short answer is no...

However, I'll give a more detailed view/explanation as to why...

Working backwards in the calibration delivery a person could add a fixed jet to a M35 carburetor like a M74 uses in its calibration. I often do.
You can also install the same main nozzle that a M74 uses.
The Venturi could also be changed to the 1 5/16" that the M74 uses.
Next we could change to a 9X throttle disc angle as found in a M74 being they are both a 1 1/2" series body.

This ultimately leaves idle and transitional circuits in our calibration. This is where things are different and the short answer of "No" comes into the equation.

The #72 small hole orifice does not exist on a M74 that is in place on a M35. The transitional bleed slot is also 0.0045" larger on a M74. The large hole remains the same on the two of them at #55.

So for those reasons and the fact that the idle circuit and transitional circuits are essentially "Fixed" in the body, we arrive at no for an answer.

For what it's worth, you'll note that the earlier model Linkerts do not idle as clean over "Time" spent Idling and then transition up as smooth from idle. The M74 models do this better.
This is partially due to the idle and transitional changes made in production and the wet flow dynamics of the cylinder heads intake tract from say a Knucklehead to a later model Panhead. Breaking things down gets technical but that's the quick answer.

I hope this helps,

Duke Kleman

[T. Cotten]

....
This ultimately leaves idle and transitional circuits in our calibration. ....

Please explain "transitional' circuit on a Linkert, Duke,

My books only list the bowl circuit, idle circuit, and power circuit,

Thanks,

....Cotten

[dukekleman]

Please explain "transitional' circuit on a Linkert, Duke,

My books only list the bowl circuit, idle circuit, and power circuit,

Thanks,

....Cotten

The transitional circuits are fixed in most carburetors including the Harley Davidson Linkerts, Bendix and Keihin Models. When the throttle disc is calibrated correctly, it will idle based off the amount of air volume leaking around the disc while resting on the idle speed stop screw and the fuel volume being delivered from the fixed idle passage.
When the disc is opened from that idle stop screw position, the air volume around the disc increases. In order to maintain a proper AFR the transitional fuel passages add additional fuel.

I hope this helps,

Duke Kleman

[T. Cotten]

The transitional circuits are fixed in most carburetors including the Harley Davidson Linkerts, Bendix and Keihin Models. When the throttle disc is calibrated correctly, it will idle based off the amount of air volume leaking around the disc while resting on the idle speed stop screw and the fuel volume being delivered from the fixed idle passage.
When the disc is opened from that idle stop screw position, the air volume around the disc increases. In order to maintain a proper AFR the transitional fuel passages add additional fuel.

I hope this helps,

Duke Kleman

No wonder I couldn't find it in the books, Duke.

That's not a circuit in itself, but only part of the idle circuit:

idle circuit 1.jpg
idle circuit 1a.jpg

idle circuit 2.jpg
The question becomes how the idle circuit reverses and purges itself; Like a toilet all at once, or can it gurgle at low RPM?

Tuning for idle, with even Scheblers with no idle slot, was never a problem for me, when everything else was in order.

I know little of modern carbs but that an added intermediate circuit makes tuning even more of a tail-chase.

....Cotten

[dukekleman]

It's impossible to go from Idle to full throttle position ( 900 rpm to say 5,000 rpm) without transitioning...The AFR (Air to Fuel Ratio) must be proper for this to occur.

All butterfly valve carburetors have a transitional circuits except some that are used on engines with mechanical governor's.

Mechanical slide carburetors have what is referred to as a Idle Bypass

The more fuel circuits we add to a carburetor, the smoother the fuel curve transitions. The more jets, the better. View it as walking upstairs that the thread and riser is built incorrectly and inconsistent, you would trip up on them and struggle if they staggered the very randomly. Weird analogy perhaps but carburetors and engines are very much like that.

A ramped fuel curve from idle to full throttle is far smoother than a 2 jet long stride fuel curve. Multiple circuits and jet adjustability makes the curve smooth (ramped).

This adds to longer engine life because the oil isn't as contaminated and circulated all the contamination through the entire engine.

When I write ECM calibrations for a EFI two cylinder v twin, I'm dealing with over 450 jets in a way... depending on the CAl. Level. Getting it correct makes the left and right foot boards or pegs equally smooth. It's very noticeable how the frequency changes throughout. There's a lot to it all.

l always say "Everything connects to Everything"

Hope this helps,

Duke Kleman