Linkert M74B

[T. Cotten]

No the opposite, I mean it is seasoned. Now once they are straighten out, it'll stay in formation longer than it did way back when it was new...

A tiny bit, Duke.

But they can still warp over and over and over.

My inspection is the same as the remedy: I swipe them criss-cross on a very large stone.

POLSHMIL.jpg

When both carb and manifold are ground, they almost 'wring' to zero daylight.
(First pic I found that shows my criss-cross cross-hatch)...

BOREGRND.jpg


Just one installation, and there's daylight. Metal moves.

....Cotten

[Laurie]

So Cotton
Where do they usually leak from?and why? bad fitment or to big a gap for the o rings?

Cheers & Beers

Ok finally got back to the Knuckle, sorted a few more issues out some relevant to issues but some not.
found I had a bad plug lead front cylinder so replaced and tested both, all good
Tried another known coil, no change
found faulty fuel rod, replaced with Carl's Peek tipped rod, all good
after no seen leaks during leak test thought I'd try spraying the inlet nipples to heads area with aerostart, (ether based) thought it would pick up at idle if sucking air, but no change.
Even tried another 74B which was rebuilt years ago for my '65 and never run, same problem!

So it starts easily, Idles ok and revs cleanly but after a 5mile run the front cylinder plug is fouled and the rear plug just a little lean, all this with the low speed needle 5 turns out and the high speed needle shut off, 1/2 turn out or 1 or 2 turns out no difference
So am i right to assume that the rear nipple must be sucking air keeping that cylinder lean?
what would you use to seal the nipple threads if thats the case?
Looks like thats where I'm heading next, unscrew nipples and re seal?
all help greatly appreciated
Cheers & Beers
Laurie

[T. Cotten]

...after no seen leaks during leak test thought I'd try spraying the inlet nipples to heads area with aerostart, (ether based) thought it would pick up at idle if sucking air, but no change.
Even tried another 74B which was rebuilt years ago for my '65 and never run, same problem!

But you did not bubble-test, Laurie?

...So it starts easily, Idles ok and revs cleanly but after a 5mile run the front cylinder plug is fouled and the rear plug just a little lean, all this with the low speed needle 5 turns out and the high speed needle shut off, 1/2 turn out or 1 or 2 turns out no difference
So am i right to assume that the rear nipple must be sucking air keeping that cylinder lean?...

A bubble-test would eliminate the need for assumptions.

...what would you use to seal the nipple threads if thats the case?
Looks like thats where I'm heading next, unscrew nipples and re seal?....

Please review http://virtualindian.org/11techleaktest.html

(Even the Seal-Lock product has its limitations, so most use original JBWeld, although it should cure a couple of weeks at least for fuel resistance.)

.....Cotten
PS: Please note the safety warning about using ether.

(I worked with a chemist badly scarred when it ignited off of a steam radiator; Hard to believe, but believe me, the scars were real.)

[Laurie]

But you did not bubble-test, Laurie?



A bubble-test would eliminate the need for assumptions.



Please review http://virtualindian.org/11techleaktest.html

(Even the Seal-Lock product has its limitations, so most use original JBWeld, although it should cure a couple of weeks at least for fuel resistance.)

.....Cotten
PS: Please note the safety warning about using ether.

(I worked with a chemist badly scarred when it ignited off of a steam radiator; Hard to believe, but believe me, the scars were real.)

Cotton I did the leak test by spraying soapy water all around the manifold and fittings no bubbles, is that what you call the bubble test?

[T. Cotten]

Cotton I did the leak test by spraying soapy water all around the manifold and fittings no bubbles, is that what you call the bubble test?

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

....Cotten

[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.

[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!

[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!

[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

[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]

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]

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]

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]

Couldn’t wait

no light as far as i could see

[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