Linkert M5 Carb

[Jdiesel25]

Looking for a correct Linkert M5 carb for a 1937 Knucklehead

[Chris Haynes]

1937 has four air cleaner screws.

[T. Cotten]

1937 has four air cleaner screws.

I've got two of those, Chris,..

But couldn't they be '38-'39 as well?

What's a dot by the 5 mean?

M5dotstp.JPG

Thanks in advance,

....Cotten

[Chris Haynes]

I have never seen a dot before.

[Jdiesel25]

I believe the 37 M5 has the stamped 4 on the side

[T. Cotten]

I believe the 37 M5 has the stamped 4 on the side

As do both of mine, JD!

Even the one without the dot.

Unfortunately, I have too little time to properly tend to them right now.

If I did, I would first inspect to see if there is a difference in the idle bleed holes. There is probably a shop dope about it which literature collectors covet too much to share.

....Cotten
PS: They weren't that rare, Chris...

M5STAMPS.jpg I never saw one of these, either!
M5FSTMP.jpg

[Jerry Wieland]

I think the 'F' is Califnonia Police carburetor.

Jerry

[T. Cotten]

I think the 'F' is Califnonia Police carburetor.

Jerry

That's what I was told, Jerry!

My point to Chris was that I never saw one (in real life.)

Logically we must ask: What was different?

....Cotten

[dukekleman]

I'm told there are a few oddities when it comes to M5 carburetors. Other manufacturers used the M5 stamping as well.
The items I've observed while working on the M5 HD models where : Body Stamping variations, fixed jet (M5F) series, different Venturi sizes used, different main nozzles used and different bolt patterns used for the A/C backing plate.

The only thing that stands out to me was Harley Davidson was learning how to calibrate this new engine model (OHV EL series). The venting locations were not taken into consideration when they rotated the carburetor 180 degrees from a UL series to a EL series.
The calibration used, per specifications in various publications, when tested, can definitely use improvements.
Analyzing the fuel delivery Data curves from the 30's Linkerts to the 60's Linkerts it's quite apparent.

As any product development goes, over Time, this is normal. The same can be said about HD's early Magnetti Marelli EFI in the 90's to the EFI Systems used on todays 2025 models. The calibration tables are VERY different. When riding both, it is quite apparent also...

Duke Kleman

[Rubone]

I have a M5 with the dot and a slightly small 5. It also is blank on the side body stamping, Mine is just 3-blank boss-8..., which kind of goes along with Duke's observations.

[T. Cotten]

...Other manufacturers used the M5 stamping as well....

What other manufacturer would be confused with a Linkert, Duke?

The items I've observed while working on the M5 HD models where : Body Stamping variations, fixed jet (M5F) series, different Venturi sizes used, different main nozzles used and different bolt patterns used for the A/C backing plate.

Did you document any of these for us, Duke?
I noted the dot and F, but have found no other variations for M5s; Replacement M55s and such, however, were hand-stamped with serif'd Ms, and I would be very suspect of anything with a smaller 5.

Please note that anything removeable such as a venturi and main nozzles would need some sort of documentation to accept as production eighty-five years later.

(Chris implied that it was the '36 productions that had two-bolt aircleaner flanges.)

Can you share any of these fuel delivery data curves? Thanks in advance,

....Cotten
PS: Is this a 'small' five, Folks?
On an M51X:
M51X stmp.jpg

Just ignore the X; That doan' mean nuttin' to a judge.

[dukekleman]

Hi Cotten,

Crocker motorcycle used a M-5 Linkert.

Stampings varied on the side of the bodies that I've seen. I've seen 2, 3 and 4 on the side of the bodies near the choke lever arm that were stamped M5 on top.

My discoveries have shown that the idle orifice is to small while the transitional orifice to to big. I also have found that a Venturi of 1.0937" is better suited than a 1.0625". The main nozzles center orifice and bleed holes are not ideally sized nor positioned. The main nozzles air bleed is positioned incorrect for an EL series engine and should be sized smaller.
The wet flow dynamics of the intake manifold and intake port cause fuel control issues as well.
When the cast iron cylinder heads heat to an operating temperature, the fuel atomization and vaporization rates change. This ok to deal with as long as it's understood not to calibrate the tune until it reaches proper operating temperature.
This applies to any engine, it's just more noticeable on this cast iron EL cylinder head and manifold design. There are a lot of areas for fuel droplets to drop out of suspension and re- form themselves. What I'm getting at is it causes complications in the calibration stability over time during operational phases.
There's a lot going on with the M5 and it got better on later series Linkerts as time went on.
To be honest, I tried to summarize things above but it gets messy. There's a difference between its runs and it runs right.
I always state that everything connects to everything so it's not all the carburetors faults...many things have to come together in the end.

Hope this helps,

Duke Kleman

[T. Cotten]

Hi Cotten,

Crocker motorcycle used a M-5 Linkert.

Stampings varied on the side of the bodies that I've seen. I've seen 2, 3 and 4 on the side of the bodies near the choke lever arm that were stamped M5 on top.

My discoveries have shown that the idle orifice is to small while the transitional orifice to to big. I also have found that a Venturi of 1.0937" is better suited than a 1.0625". The main nozzles center orifice and bleed holes are not ideally sized nor positioned. The main nozzles air bleed is positioned incorrect for an EL series engine and should be sized smaller.
The wet flow dynamics of the intake manifold and intake port cause fuel control issues as well.
When the cast iron cylinder heads heat to an operating temperature, the fuel atomization and vaporization rates change. This ok to deal with as long as it's understood not to calibrate the tune until it reaches proper operating temperature.
This applies to any engine, it's just more noticeable on this cast iron EL cylinder head and manifold design. There are a lot of areas for fuel droplets to drop out of suspension and re- form themselves. What I'm getting at is it causes complications in the calibration stability over time during operational phases.
There's a lot going on with the M5 and it got better on later series Linkerts as time went on.
To be honest, I tried to summarize things above but it gets messy. There's a difference between its runs and it runs right.
I always state that everything connects to everything so it's not all the carburetors faults...many things have to come together in the end.

Hope this helps,

Duke Kleman

I admit, Crocker carbs never crossed my benches, Duke!

Do you imply their stamps had a - between the M and 5?

If they were Linkerts, what other manufacturer made M5s?

....Cotten

[Chris Haynes]

(Chris implied that it was the '36 productions that had two-bolt aircleaner flanges.)

Only very early 1936 had only two air cleaner screws. The interesting thing is that every original 1936 carb cover I have seen was set up for a four screw carburetor body. Even though only two screws were used.

[Dave Minerva]

On my 1940 Crocker it is stamped M55C. It is a 3 line type. The second 5 is slightly smaller. The C is off the boss like the B on a M74B