Linkert M74B

[dukekleman]

Laurie,
If your carburetor body is warped more than 0.015" , I would suggest you straighten it out prior to sanding.

This will minimize the material lost when sanding which aids in retaining thread depth.

Hope this helps!
Duke

[Laurie]

Like Duffey posted, Laurie,...

Not only are there many common places to leak, some leak at "impossible" places (little 'blisters' of foam form at porosities after a half-minute or so, and yes, they do affect performance!):

MANBLSTR.jpg MANBLSR2.jpg

Those were 'plumber's' castings, but here's modern S&S O-ring leakers:
S&SPORE.jpg
S&Spore2.jpg

Without bubbles such curses could never be cured.
(Note the first two had been perforated with a port, shown here repaired,
in a frustrated attempt at some better idea, because they were not diagnosed.)

Note also that the manifold-to-carb connection cannot be bubble-tested, so please arbitrarily grind the manifold flanges to *flat*,,... because they never are!

FLNGDST4.jpg

....Cotten

Cotten
hope to get at it tomorrow, but I will also flat sand the flanges Thanks for the advice!

Cheers & Beers

[Laurie]

They can leak in many places,one is the rivet that holds the inserts in the heads.Another is the inserts to heads around the threads.If you actually have o-rings it is not stock.Either stock or modified, any point in the system can have a leak.Carb to manifold etc.

yes mate the heads were modified before I got them to O Ring type manifold

[T. Cotten]

Like Duffey posted, Laurie,...

Not only are there many common places to leak, some leak at "impossible" places (little 'blisters' of foam form at porosities after a half-minute or so, and yes, they do affect performance!):

MANBLSTR.jpg MANBLSR2.jpg

Those were 'plumber's' castings, but here's modern S&S O-ring leakers:
S&SPORE.jpg
S&Spore2.jpg

Without bubbles such curses could never be cured.
(Note the first two had been perforated with a port, shown here repaired,
in a frustrated attempt at some better idea, because they were not diagnosed.)

Note also that the manifold-to-carb connection cannot be bubble-tested, so please arbitrarily grind the manifold flanges to *flat*,,... because they never are!

FLNGDST4.jpg

....Cotten

[duffeycycles]

They can leak in many places,one is the rivet that holds the inserts in the heads.Another is the inserts to heads around the threads.If you actually have o-rings it is not stock.Either stock or modified, any point in the system can have a leak.Carb to manifold etc.

[Laurie]

As long as it was regulated, it should be sufficient, Laurie..

Its not about accuracy as much as constant supply, and fifteen psi is over-kill but prudent.

(Had to make certain you weren't using a tire pump, or worse yet, a Schrader valve upon the test plate like silly ebay offerings.)

Once again I must add, you have really beaten the odds!

....Cotten

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

Cheers & Beers

[T. Cotten]

Cotton
I hope your right! will get back to you when ive tested again, quick question though whats the best way to make sure the valves are shut?

Simple, Laurie!

Just watch the regulator; It will rise and drop as motor valves open and close, then set it at about fifteen at its highest. Its all about the pressure differential, not holding pressure, and it doesn't matter what stroke its on.

Please remember that there will always be air passing around the intake stems and guides that is orders of magnitude greater than the leaks we seek. That's why a constant supply is required, and Schrader valves give false negatives.

(The valves on Chiefs never seem to shut completely at the same time!)

....Cotten

[dukekleman]

Laurie,
I'm not sure if you asking about fuel valves or engine valves.

On the engine valves you can set the engine to TDC compression stroke. If you are doubting either Valve over lap verse compression stroke, remove your push rod cover retaining clip , raise the cover tube and verify that both pushrods spin freely with your fingers.

Valve sealing integrity can be verified by performing a cylinder leak down test.

Hope this helps,
Duke

[Laurie]

Cotton
I hope your right! will get back to you when ive tested again, quick question though whats the best way to make sure the valves are shut?

[T. Cotten]

Cotten
I'll have to admit that it probably wasn't regulated properly and therefore not constant as my regulator is pretty ordinary, so im going to buy another regulator tomorrow & try again

As long as it was regulated, it should be sufficient, Laurie..

Its not about accuracy as much as constant supply, and fifteen psi is over-kill but prudent.

(Had to make certain you weren't using a tire pump, or worse yet, a Schrader valve upon the test plate like silly ebay offerings.)

Once again I must add, you have really beaten the odds!

....Cotten

[Laurie]

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

Duke I'll check the carb tomorrow! Thanks Mate!

[Laurie]

If your conversion doesn't leak, Laurie,..

Its one in a thousand!

(Forgive me but I must ask: You are using a regulated, constant air supply, right?)

And I had great luck tuning M74Bs, even for EL Knucks. But then, everything else was in order....

...Cotten

Cotten
I'll have to admit that it probably wasn't regulated properly and therefore not constant as my regulator is pretty ordinary, so im going to buy another regulator tomorrow & try again

[T. Cotten]

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.

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.

Hope this helps,
Duke

That reminds me of the time, Duke,..

A recognizable international Indian personality (at least within the Indian zodiac) sent me his vintage-tricked brand-X M5 with shaved shafts for flow, for a re-fresh.

The throttledisc was soldered-in backwards.

He had run it righteously for years! If they weren't forgiving, they would never have become legendary.

...Cotten

[dukekleman]

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

[T. Cotten]

Ok I did a leak test using a plate similar to the https://web.archive.org/web/20250615...hleaktest.html (forgot I had 1) and no leaks,
I should mention that the heads has had an O ring manifold conversion done.

Jerry
I have a '46 thats been running a M74B for the last 8 years no problems there.

If your conversion doesn't leak, Laurie,..

Its one in a thousand!

(Forgive me but I must ask: You are using a regulated, constant air supply, right?)

And I had great luck tuning M74Bs, even for EL Knucks. But then, everything else was in order....

...Cotten