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

[T. Cotten]

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

Again, Duke,

Please show me the 'transitional circuit' on a Linkert; The idle circuit cannot be both.

The true transition from idle to power is greatly muddied by borewear, so by the original (DLX) design, there is no way to tune around it.
Modern carbs attacked it with byzantine extra circuits, instead of just allowing for the hardware to be rebuilt. Thus everything after the Linkert DCs were 'throw away'.

I have no clue what "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. " means.

But I do know that you can cobble a DLX/Linkert any which way, and if certain baselines are met (no vacuum leaks, etc.) it will at least still run.

OzPenny.JPG

PennyThrottle.jpg

.....Cotten

[dukekleman]

Again, Duke,

Please show me the 'transitional circuit' on a Linkert; The idle circuit cannot be both.

The true transition from idle to power is greatly muddied by borewear, so by the original (DLX) design, there is no way to tune around it.
Modern carbs attacked it with byzantine extra circuits, instead of just allowing for the hardware to be rebuilt. Thus everything after the Linkert DCs were 'throw away'.

I have no clue what "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. " means.

But I do know that you can cobble a DLX/Linkert any which way, and if certain baselines are met (no vacuum leaks, etc.) it will at least still run.

OzPenny.JPG

PennyThrottle.jpg

.....Cotten

Cotten,

An attempt at recalibrating around bore wear would be a bandaid, not a repair.
Some carburetors, more current modern carburetors, can not be repaired by a supply of repair parts. They are simply disposable for replacement cost reasons.
I personally don't agree with the direction things have gone.
I feel fortunate to have grown up in the era of mechanical repair/rebuild verse the current component parts replacement era...
All new products have slowly gone this direction for the last 40 plus years.
On certain items, we are forced to choose an improper band-aid repair to "make it run". Those types of repairs do indeed muddy things up as you stated.
However, there are times we can adopt modern technologies and repair things at a new like option or occasionally better than new.

The idle circuit does indeed move to the transitional circuit. The idle circuit is often included in what is referred to by some as the "low speed circuit".
It's important to understand that idle is simply that, idle.
Once the throttle disc is moved off the stop position held by the "Idle speed screw" you are no longer idling. Now your are transitioning in rpm which requires added fuel circuits to compensate for the added air flow. Those are considered fuel transitional circuits.
Obstruction of these transitional fuel passages would verify their importance and existence to the operator. Making them to small in calibration or to large in calibration allows them to "Run" but not run right...
They are fixed as I mentioned, so modifications to engine size, camshaft, air filtration, exhaust, unwanted air induction, valve size, seat angles, we can go on and on...all can not be compensated for correctly. Unfortunately people will enlarge these will small drill bits and wires. All which are irreversible. Attempts at soldering them shut and redrilling occur by some. Once again, they will run, but....EDM is your best chance at accuracy. None of this is easy as you well know.

Could modern carburetors be used in place of worn out originals, absolutely and in the right hands will run very well by comparison. We know most don't want a properly calibration Mikuni HSR or CVH design carburetor on their antique.
After all, repairing and making the antique components as good as they can be again is part of what we love about old motorcycles.
With that we have to learn to accept limitations and annoyances.

I hope this helps,

Duke Kleman

[T. Cotten]

....An attempt at recalibrating around bore wear would be a bandaid, not a repair.

That's why I repaired them Duke!

WEARFIX.jpg

No borewear means no messy transition ('flat spot', etc.)

.....Cotten

[dukekleman]

That is some beautiful workmanship Cotten!
Nicely done!

[T. Cotten]

That is some beautiful workmanship Cotten!
Nicely done!

Thanks Duke,

I hope somebody is paying attention, as I may never be able to produce another one.

....Cotten

[macca]

Thanks for all the info.I have a m35 on a stanard46 knuckle but cannot get it to run But when I fit a m74 it runs great

[T. Cotten]

Thanks for all the info.I have a m35 on a stanard46 knuckle but cannot get it to run But when I fit a m74 it runs great

Macca!

Please first inspect your carb flange for warpage, by 'striking' it criss-cross upon some emery on a flat plate:

FLNGWAVY.jpg

Felt-tip marker helps, too.

They are all distorted.
So are the manifold flanges.

....Cotten

[macca]

i have checked it & the flange .all so built up the manifold so it only just fits between the head & machined it true.I will put it back to original spec & see what happens