Linkert M74B

[Laurie]

G'Day Folks
Ive just finished my 41 Knuckle and am having trouble dialing in my M74B Linkert, motor is a fresh rebuild by a reputable engine builder who cleaned checked and re assembled the carb, the only way to get this to idle and run is to have the low speed needle out 41/2 turns and so of course it runs rich and fouls plugs, I have tried shutting off the high speed needle, no help,
At the starting procedure with the low speed needle set at 3 turns out and the choke on 1 click starts and idles nice but as soon as you turn off the choke it stalls
any and all help greatly appreciated
cheers & Beers
Laurie

[T. Cotten]

G'Day Folks
Ive just finished my 41 Knuckle and am having trouble dialing in my M74B Linkert, motor is a fresh rebuild by a reputable engine builder who cleaned checked and re assembled the carb, the only way to get this to idle and run is to have the low speed needle out 41/2 turns and so of course it runs rich and fouls plugs, I have tried shutting off the high speed needle, no help,
At the starting procedure with the low speed needle set at 3 turns out and the choke on 1 click starts and idles nice but as soon as you turn off the choke it stalls
any and all help greatly appreciated
cheers & Beers
Laurie

Generally, Laurie,...

If they wont run any way but over-rich, it means extra air is getting in some where.

The very first diagnostic is http://virtualindian.org/11techleaktest.html

Only after the manifold is absolute can we address the carb itself.

....Cotten

[Laurie]

Generally, Laurie,...

If they wont run any way but over-rich, it means extra air is getting in some where.

The very first diagnostic is http://virtualindian.org/11techleaktest.html

Only after the manifold is absolute can we address the carb itself.

....Cotten

Cheers Cotten, dont know why I didn't think of that! I'll do a leak test on the weekend.
Thanks mate!

[Jerry Wieland]

My experience is that knuckleheads do not like M-74B's. They seem to prefer a M-35.

[Laurie]

Ok I did a leak test using a plate similar to the http://virtualindian.org/11techleaktest.html (forgot I had 1) and no leaks,
I should mention that the heads has had an O ring manifold conversion done.

My experience is that knuckleheads do not like M-74B's. They seem to prefer a M-35.

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

[T. Cotten]

Ok I did a leak test using a plate similar to the http://virtualindian.org/11techleaktest.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

[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]

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

[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

[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!

[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]

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?

[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

[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

[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