Linkert M74B

[T. Cotten]

QUESTION FOR KNOWLEDGE:
Upon rebuilding an M74B if the venturi is stuck in the carb bore and one does not remove it (or fix it being stuck) will it cause any problems with the running / starting etc ?
What are the consequences?
Why go to the point of pressing it out (by force). Also i read about a "light gap".
I have never got my head around this and could not find an answer in the forum
THANKS

Did the main nozzle come out easily, Jack?

Fuel residues can combine with moisture to 'cement things together, but disassembly is manditory for cleaning the 'air correction' chamber (extreme example shown).

SNDYVNT.jpg

It is common that once the 'crust' is removed, original venturies will be quite loose, and show daylight around them;

DAYLIT88.jpg

CLNYVENT.jpg

Most break loose with penetrant and a heat lamp, but I've had plenty, especially Scheblers, that sounded like a firecracker in the sixty-ton press.


....Cotten

[Iacovos]

QUESTION FOR KNOWLEDGE:
Upon rebuilding an M74B if the venturi is stuck in the carb bore and one does not remove it (or fix it being stuck) will it cause any problems with the running / starting etc ?
What are the consequences?
Why go to the point of pressing it out (by force). Also i read about a "light gap".
I have never got my head around this and could not find an answer in the forum
THANKS

[Iacovos]

The “damn” thing fired up on the first go!! This 64 did not run for 10 years now!

Big Thanks for all the input for the linkert rebuild! Much appreciated everyone!

No gas leaks (was worried as was my first carb rebuild …..)

Oil pressure switch not working (had to check oil circulation hemce the seat being up)

[Iacovos]

With the idle screw backed out, Jack,

The disc should close completely against the bore wall at the idle bleeds. With the bleed plug removed, the disc should be visible in the middle of the idle slot:

DISKBLED.jpg
(Model shown is other than M74B, but the position is the same.)

The idle screw, when turned in to slightly open the disc for initial starting, becomes the 'closing' stop.

I must note that to inspect for daylight around the disc, the choke must open; I inspected with even the venturi removed for certainty.

....Cotten

Well noted! Thanks for your reply Cotten!

[T. Cotten]

This is fully closed and fully opened

when the disc is closed is it normal to have the gap with the idle screw all the way backed ouf?

When the disc is fully opened the lever is on the carb body stop

With the idle screw backed out, Jack,

The disc should close completely against the bore wall at the idle bleeds. With the bleed plug removed, the disc should be visible in the middle of the idle slot:

DISKBLED.jpg
(Model shown is other than M74B, but the position is the same.)

The idle screw, when turned in to slightly open the disc for initial starting, becomes the 'closing' stop.

I must note that to inspect for daylight around the disc, the choke must open; I inspected with even the venturi removed for certainty.

....Cotten

[Iacovos]

This is fully closed and fully opened

when the disc is closed is it normal to have the gap with the idle screw all the way backed ouf?

When the disc is fully opened the lever is on the carb body stop

[Iacovos]

Couldn’t wait

no light as far as i could see

[T. Cotten]

Another note on the disc installation, Jack,..

With the disc loose in the shaft, I would center it as close as possible (usually to lines scribed upon both sides of the shaft from a previous installation, or upon inspection of the freshly cut disc.) Then I would hold the disc about a quarter of the way open, and sharply tap it shut directly at the stamping with my finger.

It often took several attempts, but this usually self-centered the disc to its sweetest spot.

...Cotten
PS: Another warning about aftermarket discs: This was a fresh Tedd Cycle rebuilt carb sent to me to be saved:
TEDDBORE.jpg

[Iacovos]

When the stamping (9/X) is on the right side of the shaft when viewed from the manifold end, Jack,

This places the 9/X's compound bevel at the idle bleeds.

The primary bevel of the disc should close to match the bore walls. With the screws loosened, and the idle screw backed out, the closed disc should be centered to where any daylight is eliminated before tightening the screws. (The friction spring should be in place beneath lever, and the lever tightened where the disc is fully open, and lever stop is against the tower at the top of the flange.) With the disc tightened at its sweetest spot, the idle screw can then be turned in to where it just opens the disc.

When it is impossible to eliminate most daylight, there is wear upon the bore, or disc,..

KEYDISC.jpg
... or both. Beware also that many discs, both OEM and aftermarket, are undersized, and will never close fully. (Nearly all NOS 13° Ordnance discs were ~2 thou undersized, whether for idiot-clearance, or just to hide 'seconds' in cosmoline, is anybody's guess.)

I usually aimed at a half-thou smaller than the honed bore; Especially with 4-bolt flanges, an exact disc would require the torque-plate to be re-applied to center it perfectly!

....Cotten
PS: Incredibly, I encountered one 9/X disc that was stamped backwards:
9-XREVRS.jpg
We are all at the mercy of our own observations!

Thanks Cotten!

Really interesting with the various tolerances!! Your detailed input is appreciated!

Will look into it tomorrow and come back to you!

[T. Cotten]

Question on the throttle disc please
Above it says that the bevel on the throttle disc needs to be located by the idle and transitional circuits. Which side is that when looking on the installed throttle disc from the top of the carb (bowl on the bottom)?

thanks a lot

When the stamping (9/X) is on the right side of the shaft when viewed from the manifold end, Jack,

This places the 9/X's compound bevel at the idle bleeds.

The primary bevel of the disc should close to match the bore walls. With the screws loosened, and the idle screw backed out, the closed disc should be centered to where any daylight is eliminated before tightening the screws. (The friction spring should be in place beneath lever, and the lever tightened where the disc is fully open, and lever stop is against the tower at the top of the flange.) With the disc tightened at its sweetest spot, the idle screw can then be turned in to where it just opens the disc.

When it is impossible to eliminate most daylight, there is wear upon the bore, or disc,..

KEYDISC.jpg
... or both. Beware also that many discs, both OEM and aftermarket, are undersized, and will never close fully. (Nearly all NOS 13° Ordnance discs were ~2 thou undersized, whether for idiot-clearance, or just to hide 'seconds' in cosmoline, is anybody's guess.)

I usually aimed at a half-thou smaller than the honed bore; Especially with 4-bolt flanges, an exact disc would require the torque-plate to be re-applied to center it perfectly!

....Cotten
PS: Incredibly, I encountered one 9/X disc that was stamped backwards:
9-XREVRS.jpg
We are all at the mercy of our own observations!

[Iacovos]

Laurie,
I'd like to try and help by first asking if the spring collar is in place and installed correctly? Here's and image of a spring collar.
Screenshot_20240408-202901.png
Also I'd like to ask if the throttle disc is installed in the proper direction. It's important to have it installed correctly. If not, your idle circuit will not operate properly nor will it transition fuel correctly. Here's an image of a throttle disc. Note the bevel at the 6 o'clock position in the photo. This bevel needs to be located by the idle and transitional circuits in the correct manner to function as normal.
Screenshot_20240408-203108.png
Hope this helps,
Duke

Question on the throttle disc please
Above it says that the bevel on the throttle disc needs to be located by the idle and transitional circuits. Which side is that when looking on the installed throttle disc from the top of the carb (bowl on the bottom)?

thanks a lot

[T. Cotten]

Please note riveting tips at http://virtualindian.org/11techleaktest.html, Folks...

Its best to temper your stock before cutting oversized rivets, as it can change dimensions; I tossed large spikes in a healthy bed of coals, and fished them out the next morning.

With Knucks, please beware that the nipples seal against a very delicate lip on the head casting.

Although I have evidence of sealer on an NOS Chief cylinder, I have yet to find evidence that HD ever relied upon anything but a mechanical seal.

.....Cotten

[otis71]

Almost always if the nipple leaks the rivet does too. I enlarge the rivet hole slightly and turn a larger rivet to fit. Be sure to soften the rivet after turning with heat and ultra slow cooling. Wood stove works good for this if available. Also since the nipple isn’t a tapered thread I like to make sure the JB is not only on the threads but on the mating surfaces of the nipple and the head. Good luck!

[Laurie]

yes mate, straight from the airline into a regulator set at 15psi then out of the reg into the air fitting on the leak test plate.

Cotton I'll try it again maybe using more washing liquid in the mix!

[Laurie]

Did you use a constant, regulated air supply of no more than 15psi, Laurie?

....Cotten

yes mate, straight from the airline into a regulator set at 15psi then out of the reg into the air fitting on the leak test plate.